MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Acta Materialia' source. Fri, 19 Mar 2010 18:04:52 +0100 http://www.medworm.com/index.php?rid=3378307&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410001382%2Fabstract%3Frss%3Dyes (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378307 Thu, 18 Mar 2010 16:59:29 +0100 3378307 http://www.medworm.com/index.php?rid=3322208&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410001205%2Fabstract%3Frss%3Dyes (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322208 Tue, 02 Mar 2010 18:15:29 +0100 3322208 http://www.medworm.com/index.php?rid=3378343&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000844%2Fabstract%3Frss%3Dyes Abstract: We use molecular statics simulations with the tight-binding potential to analyze stress evolution in nanosize square prismatic gold specimens of different aspect ratios (length/width) deformed in either simple tension/compression or tension/compression. In the former case atoms on end faces are displaced axially but are free to move laterally, and in the latter case atoms on end faces are restrained from moving laterally during their axial displacement. It is found that the stress distribution in the unloaded reference configuration is non-uniform, and it satisfies the local and the global equilibrium equations. Large values of the von Mises stress and the maximum shear stress occur on atoms located at the third layer beneath the traction free surfaces forming different patterns ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378343 Wed, 17 Feb 2010 00:00:00 +0100 3378343 http://www.medworm.com/index.php?rid=3378345&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000868%2Fabstract%3Frss%3Dyes Abstract: The correlation between stacking fault energy (SFE) and deformation microstructure of high-interstitial-alloyed austenitic Fe–18Cr–10Mn–(N or N+C) alloys was investigated. As the content of the interstitial elements increased, the deformation microstructure changed in a sequence strain-induced martensitic transformation, mixture of martensite and twin, and finally deformation twin. The SFE, playing an important role in the transition of deformation microstructure, was evaluated by the Rietveld whole-profile fitting combined with the double-Voigt size–strain analysis for neutron diffraction profiles of tensile-strained bulk samples. At fixed N+C content, the ratio of mean-squared strain to stacking fault probability remained constant regardless of the accumulated strain, w... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378345 Tue, 16 Feb 2010 00:00:00 +0100 3378345 http://www.medworm.com/index.php?rid=3378342&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000832%2Fabstract%3Frss%3Dyes Abstract: Co–30wt.% Cr alloy was prepared by electro-deoxidation in molten calcium chloride at 1123K. A preliminary study was conducted into the preparation of the mixture of the Co3O4 and Cr2O3 and the formation of the non-stoichiometric, spinel structured, mixed oxide nominally labeled CoxCryO4. Constant voltage chronoamperometry was used both to prepare the alloy and to investigate its mechanism of formation. Electro-deoxidation proceeds by the simultaneous rapid reduction of CoO to Co and the slower reduction/substitution of CoxCryO4 to CaCr2O4 and Co metal. The final step of the electro-deoxidation is the reduction of CaCr2O4 to Cr metal, which alloys with the Co metal, and release of Ca2+ back into the electrolyte. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378342 Tue, 16 Feb 2010 00:00:00 +0100 3378342 http://www.medworm.com/index.php?rid=3272813&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000704%2Fabstract%3Frss%3Dyes (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272813 Mon, 15 Feb 2010 16:33:44 +0100 3272813 http://www.medworm.com/index.php?rid=3378344&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000856%2Fabstract%3Frss%3Dyes Abstract: Cryo-stage transmission electron microscopy (TEM), supported by Density Functional Theory (DFT), is employed to explore the microstructure of magnesium hydride (MgH2) powders. Mechanical milling results in deformation twinning of the hydride. The crystallography of the twins is established. DFT analysis shows that the twin unit cell is just as thermodynamically stable as the undeformed α-MgH2 matrix. It is hypothesized that the twins contribute significantly to the observed milling-induced kinetic enhancement by acting as high diffusivity paths for hydrogen. Energy-filtered TEM analysis on partially desorbed MgH2 demonstrates that nucleation and growth of metallic magnesium occurs non-uniformly. Larger powder particles are a composite of isolated magnesium grains heterogeneously... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378344 Mon, 15 Feb 2010 00:00:00 +0100 3378344 http://www.medworm.com/index.php?rid=3378341&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000807%2Fabstract%3Frss%3Dyes Abstract: The influence of a triaxial stress applied normally to shear planes and shear direction during affine shear deformation of face-centered cubic crystals on the theoretical shear strength is studied for the shear system using first-principles methods. The applied relaxation procedure guarantees that the modeled system is subjected to a superposition of shear, normal and in-plane stresses with individually adjustable in-plane and normal stress values. The theoretical shear strengths of individual elements prove to be qualitatively different functions of the superimposed stresses. In the special case of hydrostatic loading, however, these functions are qualitatively uniform. This behavior is discussed in terms of the electronic structure. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378341 Mon, 15 Feb 2010 00:00:00 +0100 3378341 http://www.medworm.com/index.php?rid=3378340&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000790%2Fabstract%3Frss%3Dyes Abstract: Microstructural evolution associated with the shear banding in nano-scale twin/matrix (T/M) lamellae of a Cu–Al alloy processed by means of dynamic plastic deformation was investigated using transmission electron microscopy (TEM) and high-resolution TEM. The development of a shear band was found to be a two-stage process, namely a nucleation stage resulting in a narrow band composed of nano-sized (sub)grains intersecting the T/M lamellae, followed by a thickening stage of the narrow band into adjacent T/M lamellae regions. The nucleation stage occurred within a narrow region of an almost constant thickness (100–200nm thick, referred to as “core” region) and consisted of three steps: (1) initiation of localized deformation (bending, necking, and detwinning) against the T/M... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378340 Mon, 15 Feb 2010 00:00:00 +0100 3378340 http://www.medworm.com/index.php?rid=3378339&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000789%2Fabstract%3Frss%3Dyes Abstract: Nanoscale incipient plastic deformation in crystalline metals occurs as the result of the collective motion of dislocations. It is known as “nanoplasticity” and is recognized as the elementary process of the macroscopic deformation. Abrupt increases in indent displacements called displacement bursts were observed in recent nanoindentation experiments; that is, the specific behavior for nanoplasticity. In the present study, experimental tests are first conducted to educe the unique nature of the nanoscale deformation. Subsequently, large-scale atomistic simulations are performed to predict the incipient plastic deformation and a new discrete dislocation model combined with the boundary element analysis is constructed to capture the collective motion of the dislocations. Our re... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378339 Mon, 15 Feb 2010 00:00:00 +0100 3378339 http://www.medworm.com/index.php?rid=3378338&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000765%2Fabstract%3Frss%3Dyes Abstract: It is often necessary to identify close-packed or nearly close-packed planes in a crystal. This can be done by inspection in crystal structures where one atom occupies each lattice point – i.e. face-centred cubic and body-centred cubic crystals. However, in more complex crystal structures intuitive inspection becomes rather difficult. The present paper describes a simple method for identifying close-packed or nearly close-packed planes in crystals containing more than one atom per lattice point. The method also distinguishes between “flat” planes, where all the atom centres lie in the plane, and “rumpled” planes, where the atom centres do not lie in the plane. The extent of the departure from true “flatness” can also be estimated. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378338 Mon, 15 Feb 2010 00:00:00 +0100 3378338 http://www.medworm.com/index.php?rid=3378337&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000753%2Fabstract%3Frss%3Dyes Abstract: Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1129}〈3362〉. The orientation relationship {111}γ//{0001}ε and 〈110〉γ//〈11–20〉ε between ε-martensite and austenite was observed but only certain variants were selected... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378337 Fri, 12 Feb 2010 00:00:00 +0100 3378337 http://www.medworm.com/index.php?rid=3378336&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000741%2Fabstract%3Frss%3Dyes Abstract: The martensite start temperature and driving force were calculated for the austenite to martensite transformation of a dual-phase bainitic ferrite–austenite steel at room temperature. The mechanical energy was estimated during the first and the second pass of equal channel angular pressing (ECAP). The applied mechanical energy during the first pass is not enough to induce the austenite to martensite transformation. However, the mechanical energy during the second pass can provide the required energy for the martensite formation. Microstructural observations by transmission electron microscopy and scanning electron microscopy of as-received and ECAPed samples confirm the formation of martensite during the second pass. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378336 Fri, 12 Feb 2010 00:00:00 +0100 3378336 http://www.medworm.com/index.php?rid=3378335&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000558%2Fabstract%3Frss%3Dyes Abstract: Small-sized indium tin oxide (ITO) nanowires were fabricated using the electron beam evaporation (EBE) technique at low temperature (∼150°C) without adding any catalyst. The ITO nanowires have a typical diameter of around 10nm and a length of more than 100nm, with body-centered cubic crystal structures that grow along the 〈100〉 directions, as revealed by transmission electron microscopy. The growth mechanism of the branched ITO nanowires was found to be a vapor–solid process. The nanowire films show a broadband anti-reflection property due to the graded refraction index from the film surface to the substrate. Enhanced field emission properties with a low turn-on electric field and a high field enhancement factor were also observed in the ITO nanowires. (Source: Acta Mate... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378335 Wed, 10 Feb 2010 00:00:00 +0100 3378335 http://www.medworm.com/index.php?rid=3378333&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000534%2Fabstract%3Frss%3Dyes Abstract: The size, surface and interface effects on the magnitude and stability of spontaneous polarization in a symmetric nanoscale ferroelectric capacitor were studied by analyzing its evolutionary trajectory based on a thermodynamic model. Analytic expressions of the Curie temperature, spontaneous polarization, critical thickness and the Curie–Weiss relation were derived, taking into account the effects of the depolarization field, built-in electric field, interfaces and surfaces. Our results show that the critical properties are not only functions of the ambient temperature, misfit strain and electromechanical boundary conditions, but also depend on the characteristics of electrodes, surfaces and interfaces, through the incomplete charge compensation, near-surface variation of polar... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378333 Wed, 10 Feb 2010 00:00:00 +0100 3378333 http://www.medworm.com/index.php?rid=3378334&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000546%2Fabstract%3Frss%3Dyes Abstract: The effects of wire diameter and grain size on the melting point of Ni nanowires with and without oxide capping were systematically examined. It was found that, for uncapped Ni nanowires, the melting point drops monotonically with grain size and also with the nanowire diameter; for oxide-capped Ni nanowires, the melting point rises when the nanowire diameter is decreased. Findings indicate that: (i) the reduced cohesive energy of under-coordinated atoms at the surface skin or grain boundaries and the fraction of such under-coordinated atoms dominate the undercooling of pure Ni nanowires; (ii) bond nature alteration by oxidation strengthens the surface bonds and hence results in the observed overheating; (iii) the bonds in the core interior retain their bulk nature, making contrib... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378334 Mon, 08 Feb 2010 00:00:00 +0100 3378334 http://www.medworm.com/index.php?rid=3378332&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000509%2Fabstract%3Frss%3Dyes Abstract: Nanocrystalline titanium films of different thicknesses, sputtered on sapphire substrates, were charged electrochemically with hydrogen. Hydrogen absorption and the thermodynamics of the nanocrystalline Ti–H thin film system were studied using electromotive force (EMF) measurements. The phase boundaries obtained from the EMF–pressure–concentration curves were confirmed by X-ray diffraction, complemented by in situ stress measurements during hydrogen charging. The change in the stress increase with hydrogen concentration was found to be in good agreement with the obtained phase boundaries. In comparison to bulk Ti–H system, considerable changes, such as shifted phase boundaries, and narrowed and sloped miscibility gaps, were observed in Ti–H thin films. These changes var... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378332 Mon, 08 Feb 2010 00:00:00 +0100 3378332 http://www.medworm.com/index.php?rid=3378331&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000492%2Fabstract%3Frss%3Dyes Abstract: Eu3+-doped transparent nanocomposite of SiO2–Al2O3–NaF–LaF3 was fabricated by melt-quenching and subsequent heating. X-ray diffraction and transmission electron microscopy analyses evidenced that hexagonal LaF3 nanocrystals were homogeneously precipitated among the aluminosilicate glass matrix. The distribution of Eu3+ ions in the nanocomposite was investigated by energy dispersive X-ray spectroscopy, photoluminescence and time-resolved luminescence spectra. The nanocomposite exhibited intense blue and green emissions originating from the 5D1,2,3 levels of Eu3+ incorporated in the low-phonon-energy LaF3 nanocrystals, and red emission corresponding to the Eu3+:5D0→7FJ (J=0,1,2,3,4) transitions, under the excitation of single wavelength light at 394nm. By adjusting the Eu3+... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378331 Mon, 08 Feb 2010 00:00:00 +0100 3378331 http://www.medworm.com/index.php?rid=3378330&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000480%2Fabstract%3Frss%3Dyes Abstract: The deformation microstructures of Al and Al–Mn {110}〈112〉 single crystals have been characterized after room temperature channel-die compression up to true strains of 2.1. The evolution of local misorientations and microband structures were quantified by high-resolution electron backscatter diffraction in a field emission gun scanning electron microscope and their alignments compared with the traces of active slip planes and macroscopic shear stress planes. During plane-strain compression these “Brass” oriented crystals remain stable in terms of the final, average, orientation, with a small orientation spread. However, the microband alignment varies with strain and also with solute content. There is a general tendency for the microbands to be both crystallographic and ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378330 Mon, 08 Feb 2010 00:00:00 +0100 3378330 http://www.medworm.com/index.php?rid=3378329&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000479%2Fabstract%3Frss%3Dyes Abstract: Positron annihilation spectroscopy (PAS), indentation, nanoindentation experiments and scanning electron microscopy (SEM) observations were performed on Al2O3–ZrO2 laminates samples to assess the effect of residual stresses on their mechanical and microstructural properties. Layered samples were implemented by slip-casting, constituted by two thin Al2O3 external layers and an intermediate thick one, consisting of a mixture of Al2O3 and monoclinic ZrO2 in the range 0–30 vol.%. In these systems residual tensile stresses fields were generated inside the external layers during cooling from the sintering temperature, by the expansion of the adjacent ZrO2-containing layer. SEM observations showed the microstructural effects due to the level of tension related to the zirconia conten... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378329 Mon, 08 Feb 2010 00:00:00 +0100 3378329 http://www.medworm.com/index.php?rid=3378328&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000467%2Fabstract%3Frss%3Dyes Abstract: A finding by Benzerga et al. (Acta Mater 2001; 49:3071) that the yield strength of Al–7Si–0.3Mg castings is smaller for castings with a fine secondary dendrite arm spacing (SDAS) than for those with a coarse SDAS is revisited. Previous experimental data for Al–Si–Mg castings are reviewed, and new experiments carried out, both on the original castings used in Benzerga et al. and on Al–Si binary alloy castings whose microstructures more closely conform to the theoretical model of Benzerga et al. The experimental results show that the inverse size effect reported by Benzerga et al. was a consequence of different heat-treatments applied to the original castings, rather than to any intrinsic size effect. The present results confirm that there is a negligibly small size effec... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378328 Mon, 08 Feb 2010 00:00:00 +0100 3378328 http://www.medworm.com/index.php?rid=3378327&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000455%2Fabstract%3Frss%3Dyes Abstract: In SiC sintered with Al, B and C additions (ABC–SiC), the presence of Y in the Al–Si–O–C grain-boundary phase leads to less frequent crack deflection and lower toughness. When Y is absent from the grain-boundary phase and remains in the triple pockets, crack deflection is restored, and higher toughness results from grain-bridging mechanisms. The observations are consistent with elastic modulus changes in the intergranular phase, which depend on their yttria and silica content, and indicate that these can play an important role in determining crack deflection. While high-toughness ceramics such as ABC–SiC and Si3N4 rely on sintering additives forming crack-deflecting intergranular films, the present case is a striking example where the presence of a segregant in the grai... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378327 Mon, 08 Feb 2010 00:00:00 +0100 3378327 http://www.medworm.com/index.php?rid=3378317&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000327%2Fabstract%3Frss%3Dyes Abstract: The Bordoni relaxation in fcc metals is generally assumed to result from thermally activated kink-pair formation in dislocation segments aligned along Peierls valleys in crystallographic close-packed directions. Objections against this interpretation have been raised by pointing out, that, at the small stresses applied in the experiments, the Paré condition is not satisfied and that the Peierls stress derived from the experiments by far exceeds the experimental values for the flow stress extrapolated to 0K. It is shown that, when the bow-out configuration of a dislocation segment is treated as a kink-chain, and when the splitting of dislocation into partials is accounted for, both objections cannot be maintained. Under the assumption that the kink mobility is high and using anal... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378317 Mon, 08 Feb 2010 00:00:00 +0100 3378317 http://www.medworm.com/index.php?rid=3378316&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000315%2Fabstract%3Frss%3Dyes We report the results for the following systems: AgHf, AlHf, AuHf, BaHf★, BeHf, BiHf, CaHf★, CdHf, CoHf, CrHf, CuHf, FeHf, GaHf, HfHg, HfIn, HfIr, HfK★, HfLa★, HfLi★, HfMg, HfMn, HfMo,HfNa★, HfNb★, HfNi, HfOs, HfPb, HfPd, HfPt, HfRe, HfRh, HfRu, HfSc, HfSn, HfSr★, HfTa★, HfTc, HfTi, HfTl, HfV★, HfW, HfY★, HfZn and HfZr (★=systems in which the ab initio method predicts that no compounds are stable). (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378316 Mon, 08 Feb 2010 00:00:00 +0100 3378316 http://www.medworm.com/index.php?rid=3378326&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000431%2Fabstract%3Frss%3Dyes Abstract: The mechanical behavior of an AZ31Mg sheet has been investigated at high strain rate (103s−1) and compared with that observed at low rates (10−3s−1). Dynamic tests were carried out using a Hopkinson bar at temperatures between 25 and 400°C. Tensile tests were carried out along the rolling and transverse directions and compression tests along the rolling and the normal directions in both strain rate ranges. The tension–compression yield asymmetry as well as the yield and flow stress in-plane and out-of-plane anisotropies were investigated. The microstructure of the initial and tested samples was examined by electron backscatter diffraction. The dynamic mechanical behavior is characterized by the following observations. At high temperatures the yield asymmetry and the yiel... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378326 Thu, 04 Feb 2010 00:00:00 +0100 3378326 http://www.medworm.com/index.php?rid=3378325&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964541000042X%2Fabstract%3Frss%3Dyes Abstract: Properties of basal and first order prism plane dislocations with Burgers vector 1/3 〈〉 in α-Zr have been investigated by computer simulation. Results for a recent interatomic potential (MA07) are assessed and compared with an older one (AWB95). The elastic constants have been calculated with the inner relaxations allowed for and the energy and vector of metastable stacking faults have been determined and compared with published ab initio estimates. The core of the screw dislocation spreads principally in the prism plane in the MA07 model, in contrast to basal plane dissociation in the AWB95 model, and the prism-to-basal ratio of the Peierls stress for the screw is 0.28 with the MA07 model, compared with 3.31 with the AWB95 model. Simulation of the dynamics of dislocation mo... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378325 Wed, 03 Feb 2010 00:00:00 +0100 3378325 http://www.medworm.com/index.php?rid=3378324&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964541000039X%2Fabstract%3Frss%3Dyes Abstract: First-principles’ calculations of GGA and GGA+U type have been performed for γ-Fe23C6, a complex iron carbide with 116 atom in the unit cell. GGA results were found to be in better agreement with experimental data than GGA+U results. Various occupancies for Wyckoff positions and corresponding magnetic orderings have been explored. Our calculations reveal that the crystal structure is composed of a framework of strongly linked Fe atoms, and additional stabilizing Fe and C atoms positioned in cavities. The local electronic and magnetic properties vary strongly among the non-equivalent Fe sites in γ-Fe23C6. The lattice parameters of γ-Fe23C6 match those of austenite well. Surprisingly, pure γ-Fe23C6 is found to be more stable than commonly occurring θ-Fe3C cementite. Moreover... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378324 Mon, 01 Feb 2010 00:00:00 +0100 3378324 http://www.medworm.com/index.php?rid=3378323&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000388%2Fabstract%3Frss%3Dyes Abstract: Synchrotron X-ray tomography was performed during in situ fatigue crack propagation in two small-size specimens made of nodular graphite cast iron. While direct image analysis allows us to retrieve the successive positions of the crack front, and to detect local crack retardation, volume correlation allows for the measurement of displacement fields in the bulk of the specimen. The stress intensity factors (SIFs), which are extracted from the measured displacement fields and the corresponding local crack growth rate all along the front, are in good agreement with published results. In particular, it is possible to link the non-propagation of a crack with crack closure in the crack opening displacement maps or with a local value of the measured SIF range. It is shown that a non-uni... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378323 Mon, 01 Feb 2010 00:00:00 +0100 3378323 http://www.medworm.com/index.php?rid=3378322&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000376%2Fabstract%3Frss%3Dyes Abstract: Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches. Fragmentation testing was used in the present study as a means of interface characterization of a silicon–nitride-coated polyimide substrate. During the test, after an initial rapid segmentation–cracking phase, the coating fragments developed edge delaminations which propagated in a stable manner with further increase in the applied strain. The debonding process was modelled by the finite element method incorporating a cohesive zone at the front of the interfacial crack. The edge cracks were found to be dominated by mode II loading. By fitting the predicted delamination evolution to the experimental da... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378322 Mon, 01 Feb 2010 00:00:00 +0100 3378322 http://www.medworm.com/index.php?rid=3378321&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000364%2Fabstract%3Frss%3Dyes Abstract: The 18R and 14H long-period stacking ordered structures formed in Mg–Y–Zn alloys are examined systematically using electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. In contrast to that reported in previous studies, the 18R structure is demonstrated to have an ordered base-centred monoclinic lattice, with Y and Zn atoms having an ordered arrangement in the closely packed planes. Furthermore, the composition of 18R is suggested to be Mg10Y1Zn1, instead of the Mg12Y1Zn1 composition that is commonly accepted. The 14H structure is also ordered. It has a hexagonal unit cell; the ordered distribution of Y and Zn atoms in the unit cell is similar to that in the 18R and its composition is Mg12Y1Zn1. The 18R unit cell has three ABCA-type ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378321 Mon, 01 Feb 2010 00:00:00 +0100 3378321 http://www.medworm.com/index.php?rid=3378320&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000352%2Fabstract%3Frss%3Dyes Abstract: Recent neutron and X-ray scattering measurements show intrinsic localized modes (ILMs) in metallic uranium and ionic sodium iodide. Here, the role ILMs play in the behavior of these materials is examined. With the thermal activation of ILMs, thermal expansion is enhanced, made more anisotropic, and, at a microscopic level, becomes inhomogeneous. Interstitial diffusion, ionic conductivity, the annealing rate of radiation damage, and void growth are all influenced by ILMs. The lattice thermal conductivity is suppressed at the ILM activation temperature, while no impact is observed in the electrical conductivity. This complement of transport properties suggests that ILMs could improve thermoelectric performance. Ramifications also include thermal ratcheting, a transition from brittl... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378320 Mon, 01 Feb 2010 00:00:00 +0100 3378320 http://www.medworm.com/index.php?rid=3378319&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000340%2Fabstract%3Frss%3Dyes Abstract: TiAlN/VN multilayer coatings exhibit excellent dry sliding wear resistance and low friction coefficient, reported to be associated with the formation of self-lubricating V2O5. To investigate this hypothesis, dry sliding ball-on-disc wear tests of TiAlN/VN coatings on flat stainless steel substrates were undertaken against Al2O3 at 25°C, 300°C and 635°C in air. The coating exhibited increased wear rate with temperature. The friction coefficient was 0.53 at 25°C, which increased to 1.03 at 300°C and decreased to 0.46 at 635°C. Detailed investigation of the worn surfaces was undertaken using site-specific transmission electron microscopy (TEM) via focused ion beam (FIB) microscopy, along with Fourier transform infrared (FTIR) and Raman spectroscopy. Microstructure and tribo-in... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378319 Mon, 01 Feb 2010 00:00:00 +0100 3378319 http://www.medworm.com/index.php?rid=3378315&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000303%2Fabstract%3Frss%3Dyes Abstract: The selective dissolution behavior of Ti–41 at.% Al single crystals having a α2/γ-lamellar structure with a lamellar thickness in the range 20nm to 1μm have been investigated in 0.5M NaCl aqueous solution focusing on the effect of lamellar thickness on the dissolution of γ-lamellae. In the case where γ-lamellae were thicker than ∼100nm on average, γ-lamellae were selectively dissolved and, as a result, crevasses whose widths were close to the γ-lamellae thicknesses were formed. However, not all γ-lamellae were dissolved and the distribution of crevasses was much less uniform compared with that of the γ-lamellae. On the other hand, when the average γ-lamellae thickness was (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378315 Mon, 01 Feb 2010 00:00:00 +0100 3378315 http://www.medworm.com/index.php?rid=3322258&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000406%2Fabstract%3Frss%3Dyes Abstract: Representatives (AgY, CuY, AgEr, CuDy, MgY and MgCe) of the newly discovered family of ductile stoichiometric B2 intermetallic (metal–rare-earth element, MR) compounds were characterized by X-ray diffraction, to determine if their anomalous ductility is related to an exceptional level of phase purity, lack of chemical ordering or a strong crystallographic texture. Brittle NiAl served as an anti-type in this study. We found that all of the rare-earth compounds, except MgY, have a significant volume fraction (∼5–20vol.%) of second phases (M2R intermetallics and R2O3 oxides), which has not been reported in previous studies of these materials. The most ductile of observed MR compounds, AgY, is highly ordered. A moderate texture was observed in AgY, which may explain its higher ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322258 Mon, 01 Feb 2010 00:00:00 +0100 3322258 http://www.medworm.com/index.php?rid=3322255&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000261%2Fabstract%3Frss%3Dyes Abstract: A rigorous mathematical approach based on the causal cone and stochastic geometry concepts is used to derive new exact expressions for transformation kinetics theory. General expressions for the mean volume density and the volume fraction are derived for both surface and bulk nucleation in a general Borel subset of . In practice, probably any specimen shape of engineering interest is going to be a Borel set. An expression is also derived for the important case of polyhedral shape, in which surface nucleation may take place on the faces, edges and vertices of the polyhedron as well as within the bulk. Moreover, explicit expressions are given for surface and bulk nucleation for three specific shapes of engineering relevance: two parallel planes, an infinitely long cylinder and a sp... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322255 Mon, 01 Feb 2010 00:00:00 +0100 3322255 http://www.medworm.com/index.php?rid=3378318&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000339%2Fabstract%3Frss%3Dyes Abstract: In many multi-component systems, phases can be considered stoichiometric. If two phases not stably coexisting are brought into contact, multiple new phases may nucleate at the interface and develop into a sequence of layers with different phase compositions, which grow between the original phases. Inert markers at the original contact may show “splitting” of the marker (Kirkendall) plane, called polyfurcation. Nearly exclusively binary systems have been studied theoretically or experimentally. A thermodynamic model for the kinetics of diffusional phase transformation in multi-component systems and motion of the polyfurcated Kirkendall plane is derived by the thermodynamic extremal principle. The degrees of freedom of the system are discussed rigorously. The model is demonstra... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378318 Fri, 29 Jan 2010 00:00:00 +0100 3378318 http://www.medworm.com/index.php?rid=3378314&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000285%2Fabstract%3Frss%3Dyes Abstract: Convection during directional solidification can cause defects such as freckles and misoriented grains. To gain a better understanding of conditions associated with the onset of convective instabilities, flow was investigated using three-dimensional (3D) computational fluid dynamics simulations in an experimentally obtained dendritic network. A serial-sectioned, 3D data set of directionally solidified nickel-base superalloy measuring 2.3×2.3×1.5mm was used to determine the permeability for flow parallel and normal to the solidification direction as a function of solid fraction (fS). Anisotropy of permeability varies significantly from 0.4 (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378314 Fri, 29 Jan 2010 00:00:00 +0100 3378314 http://www.medworm.com/index.php?rid=3378313&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964541000025X%2Fabstract%3Frss%3Dyes This study investigated the cyclic and static fatigue properties of 10μm thick, deep reactive ion etched, monocrystalline silicon films. Stress–life fatigue curves and fatigue degradation rates vs. stress curves were generated at both 4 and 40kHz, at 30°C, 50% relative humidity (RH). A significant frequency effect was observed, with shorter fatigue lives and faster damage accumulation rates at 4kHz. Static fatigue was also observed with shorter static lifetimes at 80°C, 90% RH than at 30°C, 50% RH. Fracture surface evaluation did not reveal any major difference between cyclically and statically fatigued devices. These experimental results confirm that the fatigue of micron-scale silicon is not purely mechanical. The study also proposes a fatigue scenario based on time-dependent subcr... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378313 Fri, 29 Jan 2010 00:00:00 +0100 3378313 http://www.medworm.com/index.php?rid=3322256&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000273%2Fabstract%3Frss%3Dyes Abstract: The synthesis of AlNi from thermally activated equimolar powder mixtures of aluminium and nickel was monitored in situ and acquired diffraction patterns every 2s or less. The analysis of diffraction patterns permitted establishment of its kinetics, which could be modeled according to an equation expressed as . From 1530 to an activation energy of 9±2kJmol−1 was estimated. Also, the crystallite size evolution on cooling was established to vary from nm at 1530°C to nm at 180°C. Finally, the reaction was found to occur through the melting of aluminium and the subsequent dissolving of nickel to form the polycrystalline single-phase product, AlNi. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322256 Fri, 29 Jan 2010 00:00:00 +0100 3322256 http://www.medworm.com/index.php?rid=3322257&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000297%2Fabstract%3Frss%3Dyes Abstract: The plastic deformation behavior of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy was investigated by compression testing at room temperature. The multi-peak stress oscillations of the true stress–strain curve, characterized by a stress plateau, initial strain-hardening, followed by strain-softening and a second strain-hardening stages, is observed in a titanium alloy for the first time. The experimental results show that the above four-stage plastic deformation behavior is caused by a change in the dominant deformation mechanisms. At the stress plateau stage, the alloy deforms via multiple plastic deformation mechanisms. The initial strain hardening is caused mainly by tangling of dislocations. Subsequent strain softening is due to the formation of kink bands. The second strain har... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322257 Thu, 28 Jan 2010 00:00:00 +0100 3322257 http://www.medworm.com/index.php?rid=3212108&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000169%2Fabstract%3Frss%3Dyes (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212108 Wed, 27 Jan 2010 16:45:20 +0100 3212108 http://www.medworm.com/index.php?rid=3378309&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000054%2Fabstract%3Frss%3Dyes Abstract: The introduction at moderate temperature of nitrogen in the 316L austenitic stainless steel by plasma nitriding modifies the crystallographic texture in the very near surface region. The evolution of texture components has been quantitatively characterized by electron backscattered diffraction. The analysis of these experiments shows that the amplitude of the lattice rotation as well as the direction of rotation are directly related to the initial orientation of each grain. The retexturing behaviour is consistent with the lattice rotation upon tensile elongation of polycrystalline materials predicted by the Taylor model. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378309 Wed, 27 Jan 2010 00:00:00 +0100 3378309 http://www.medworm.com/index.php?rid=3378312&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000236%2Fabstract%3Frss%3Dyes Abstract: Cascade simulations in single crystal and nanocrystalline SiC have been conducted in order to determine the role of grain boundaries and grain size on defect production during primary radiation damage. Cascades are performed with 4 and 10keV silicon as the primary knock-on atom (PKA). Total defect production is found to increase with decreasing grain size, and this effect is shown to be due to increased production in grain boundaries and changing grain boundary volume fraction. In order to consider in-grain defect production, a new mapping methodology is developed to properly normalize in-grain defect production rates for nanocrystalline materials. It is shown that the presence of grain boundaries does not affect the total normalized in-grain defect production significantly (the ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378312 Mon, 25 Jan 2010 00:00:00 +0100 3378312 http://www.medworm.com/index.php?rid=3322254&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000248%2Fabstract%3Frss%3Dyes Abstract: Various models for simulating dendritic solidification have been proposed in the past. However, those models based on cellular automata (adopting the virtual front-tracking (VFT) concept) are often only suitable for the consideration of one alloying element. As typical industrial alloys are constituted of numerous alloying elements, the application of these models to practical alloys is therefore rather limited. In order to overcome this drawback, a new, modified VFT model, which allows for the treatment of several alloying elements in the low Péclet number regime, is presented. By a new and effective approach, based on a functional extrapolation of the concentration gradient, we are able to study dendritic growth in multicomponent Fe–C–Si–Mn–P–S alloys. Comparisons wi... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322254 Mon, 25 Jan 2010 00:00:00 +0100 3322254 http://www.medworm.com/index.php?rid=3322253&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964541000011X%2Fabstract%3Frss%3Dyes Abstract: First-principles density functional theory calculations are used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors are calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbor Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. We predict that the triple defect mechanism has the lowest activation energy and is the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms is also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings. (Source: A... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322253 Fri, 22 Jan 2010 00:00:00 +0100 3322253 http://www.medworm.com/index.php?rid=3322252&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000108%2Fabstract%3Frss%3Dyes Abstract: In this paper, we present a novel approach for predicting the elastic fields in three-dimensional voxel-based microstructure datasets subjected to uniform periodic boundary conditions. This new formalism has its theoretical roots in the statistical continuum theories developed originally by Kroner. However, in the approach described by Kroner the terms in the series were established by selecting a reference medium and numerically evaluating a complex series of nested convolution integrals. This approach is largely hampered by the principal value problem and exhibits high sensitivity to the properties of the selected reference medium. In the present work, we have recast the same series expressions into much more computationally efficient representations using discrete Fourier tran... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322252 Fri, 22 Jan 2010 00:00:00 +0100 3322252 http://www.medworm.com/index.php?rid=3378311&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000091%2Fabstract%3Frss%3Dyes Abstract: A correlation between composition, microstructure, and magnetic properties of sputter-deposited CoFeSiB alloy films has been studied. Various analytical tools and micromagnetic models were employed to understand the details of microstructural evolution and magnetic reversal processes, respectively. The CoFeSiB alloy film shows significantly different microstructure and magnetic properties depend on the Co concentration. When the Co concentration is below 75 at.%, the alloy has an amorphous phase exhibiting magnetic softness with negative remanence. Meanwhile, beyond 75 at.%, the structure consists of nanocrystals precipitated in the amorphous matrix, which becomes magnetically hard with positive remanence as well as antiferromagnetic exchange coupling. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378311 Thu, 21 Jan 2010 00:00:00 +0100 3378311 http://www.medworm.com/index.php?rid=3378310&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000078%2Fabstract%3Frss%3Dyes Abstract: A method has been developed for fabricating millimeter cell size cellular lattice structures with square and diamond collinear truss topologies from 240μm diameter Ti–6Al–4V-coated SiC monofilaments (titanium matrix composite (TMC) monofilaments). Lattices with relative densities in the range 10–20% were manufactured and tested in both compression and shear. Because of the very high strength of the TMC monofilaments, the compressive strengths of both topology lattices were dominated by elastic buckling of the constituent struts. However, under shear loading, some of the struts are subjected to tensile stresses and failure is then set by tensile fracture of the monofilaments. Analytical expressions are derived for the elastic moduli and strength of both lattice topologies a... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378310 Thu, 21 Jan 2010 00:00:00 +0100 3378310 http://www.medworm.com/index.php?rid=3322250&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000066%2Fabstract%3Frss%3Dyes Abstract: Based on previous work by the authors the diffusion equations for a multicomponent solid are derived. Generation and annihilation of vacancies are described by an evolution law which is directly coupled with an eigenstrain rate. Manning’s correlation factor f is used in the kinetic factor for diffusion of vacancies. In addition to presentation of the diffusion equations, a rigorous treatment of the boundary conditions, assuming no or an ideal source and sink for vacancies at the surface, is presented. As an instructive example development of the site fractions of the components and the eigenstress state are demonstrated for a multicomponent chemically inhomogeneous layer on a substrate. Both the role of nonlinear terms and the correlation factor f in the diffusion equations are... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322250 Thu, 21 Jan 2010 00:00:00 +0100 3322250 http://www.medworm.com/index.php?rid=3322251&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964541000008X%2Fabstract%3Frss%3Dyes Abstract: The effect of Y incorporation into cubic Cr–Al–N (B1) was studied using ab initio calculations, X-ray diffraction and energy-dispersive X-ray analysis of sputtered quaternary nitride films. The data obtained indicate that the Y incorporation shifts the critical Al content, where the hexagonal (B4) structure is stable, to lower values. The calculated critical Al contents of x≈0.75 for Cr1−xAlxN and x≈0.625 for Cr1−x−yAlxYyN with y=0.125 are consistent with experimentally obtained values of x=0.69 for Cr1−xAlxN and x=0.68 and 0.61 for Cr1−x−yAlxYyN with y=0.02 and 0.06, respectively. This may be understood based on the electronic structure. Both Cr and Al can randomly be substituted by Y. The substitution of Cr by Y increases the phase stability due to depletion... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322251 Wed, 20 Jan 2010 00:00:00 +0100 3322251 http://www.medworm.com/index.php?rid=3322249&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000042%2Fabstract%3Frss%3Dyes We report here the effects of a good dispersion of as much as 10wt.% multiwalled carbon nanotubes (MWCNTs) on the mechanical properties of dense alumino-borosilicate glass ceramics (ABS) prepared by an ultrasonication-assisted sol–gel technique followed by hot pressing (950°C; 2h; Ar atmosphere). The fracture toughness and flexural strength of the nanocomposites increased with increasing MWCNT content up to 10wt.%. The ABS–10wt.% MWCNT nanocomposite possessed nearly double the strength of the unreinforced ABS, accompanied by ∼150% improvement in fracture toughness. However, a further increase in MWCNT content to 15wt.% resulted in a modest deterioration of the mechanical properties due to agglomeration of the MWCNTs. The carbon nanotubes have been observed to bridge crack openings o... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322249 Wed, 20 Jan 2010 00:00:00 +0100 3322249 http://www.medworm.com/index.php?rid=3378308&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000030%2Fabstract%3Frss%3Dyes Abstract: The microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{110}〈001〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{110}〈001〉, brass{110}〈112〉, M{110}〈111〉 and H{110}〈001〉, were then cut out and further compressed in channel-die by a few per ce... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3378308 Mon, 18 Jan 2010 00:00:00 +0100 3378308 http://www.medworm.com/index.php?rid=3322240&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009045%2Fabstract%3Frss%3Dyes Abstract: Zirconium oxycarbide powders with controlled composition ZrC0.94O0.05 were synthesized using the carboreduction of zirconia. They were further subjected to spark plasma sintering (SPS) under several applied loads (25, 50, 100MPa). The densification mechanism of zirconium oxycarbide powders during the SPS was studied. An analytical model derived from creep deformation studies of ceramics was successfully applied to determine the mechanisms involved during the final stage of densification. These mechanisms were elucidated by evaluating the stress exponent (n) and the apparent activation energy (Ea) from the densification rate law. It was concluded that at low macroscopic applied stress (25MPa), an intergranular glide mechanism (n⩽2) governs the densification process, while a disl... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322240 Mon, 18 Jan 2010 00:00:00 +0100 3322240 http://www.medworm.com/index.php?rid=3322248&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645410000029%2Fabstract%3Frss%3Dyes Abstract: Nanocrystalline copper is considered to be a candidate for electrical contacts for dynamic systems because of its intrinsic conductivity and enhanced fretting resistance. However, the enhanced electron scattering at high-density grain boundaries significantly deteriorates the overall conductivity of nanocrystalline copper. Recent studies suggest that nanosized twin boundaries in copper might be a solution to such a dilemma. To better understand the general mechanical behavior of nanotwin boundaries, we conducted molecular dynamics simulation studies to investigate responses of both nanotwin and nanograin boundaries in copper to stress at the nanoscale, particularly in the critical range of 5–25nm where the inverse Petch–Hall relation (P–H) may occur in nanocrystalline coppe... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322248 Fri, 15 Jan 2010 00:00:00 +0100 3322248 http://www.medworm.com/index.php?rid=3322243&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009070%2Fabstract%3Frss%3Dyes This article reports the first investigations of CuIn1−xGaxSe2 (CIGSe) polycrystalline thin films by means of atom probe tomography. Attention is focused on the distribution of Na atoms within the films. Both Na-containing and Na-free CIGSe thin films have been investigated. When Na is available during the CIGSe coevaporation, it is observed to be mainly segregated at the grain boundaries of the films; however, it is also detected within the grains of CIGSe at very low concentration. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322243 Thu, 14 Jan 2010 00:00:00 +0100 3322243 http://www.medworm.com/index.php?rid=3322238&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009021%2Fabstract%3Frss%3Dyes Abstract: The present paper demonstrates the effect of switching stresses on domain evolution and fracture toughening during quasi-static crack growth in elastically isotropic ferroelastic single crystals with transversally isotropic ferroelastic strains. With a simple switching algorithm and crack propagation procedure, domain evolution is simulated in an exemplary material with semi-infinite crack under mode I loading, starting from a mono-domain configuration. Domain reorientation is found to be strongly affected by switching stresses, which therefore have to be considered in the context of domain evolution modelling and fracture toughening. Before the onset of crack growth a needle-like domain is formed at the tip of the stationary crack, but this does not effect the crack tip stress i... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322238 Thu, 14 Jan 2010 00:00:00 +0100 3322238 http://www.medworm.com/index.php?rid=3322247&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009112%2Fabstract%3Frss%3Dyes Abstract: Phase transformations during nitriding of a ternary carbon iron-based alloy Fe–3%Cr–0.345%C were studied, aiming for a better understanding of residual stresses generation and evolution. The relationship between the precipitation of Cr7C3 carbides and CrN nitrides, the induced volume change and the mechanical properties were investigated at three distinct depths of the diffusion zone. The relaxation of residual stresses arose through phase transformations according to the diffusion of nitrogen but also of carbon. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322247 Wed, 13 Jan 2010 00:00:00 +0100 3322247 http://www.medworm.com/index.php?rid=3322246&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009100%2Fabstract%3Frss%3Dyes Abstract: The name “Gum Metal” has been given to a set of β-Ti alloys that achieve exceptional elastic elongation and, with appropriate preparation, appear to deform by a dislocation-free mechanism triggered by elastic instability at the limit of strength. We have studied the compressive deformation of these materials with in situ nanocompression in a quantitative stage in a transmission electron microscope. The samples studied are cylindrical nanopillars 80–250nm in diameter. The deformation pattern is monitored in real time using bright-field microscopy, dark-field microscopy or electron diffraction. Interesting results include the following: (i) nanopillars approach, and in several examples appear to reach, ideal strength; (ii) in contrast to conventional crystalline materials, t... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322246 Wed, 13 Jan 2010 00:00:00 +0100 3322246 http://www.medworm.com/index.php?rid=3322245&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009094%2Fabstract%3Frss%3Dyes Abstract: Magnetic shape-memory alloys tend to deform via magnetic-field-induced and stress-induced twin-boundary motion. The rather low martensite transformation temperature of ternary Ni–Mn–Ga limits the operating temperature for potential applications. By alloying 5at.% cobalt, the martensite transformation temperature and the Curie temperature was increased from 70 and 110°C respectively up to 160°C. In the single crystalline samples two non-modulated structures with tetragonal and orthorhombic lattices were found. The non-modulated orthorhombic structure has similar lattice parameters to the pseudo-orthorhombic 14M Ni–Mn–Ga phase. The single crystal specimen with the non-modulated orthorhombic structure exhibited a cyclic permutation of all three crystallographic axes in res... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322245 Wed, 13 Jan 2010 00:00:00 +0100 3322245 http://www.medworm.com/index.php?rid=3322244&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009082%2Fabstract%3Frss%3Dyes Abstract: Replication of metallic high-aspect-ratio microscale structures by direct compression molding is a promising microfabrication technique. In this paper, the micromolding response of elemental Cu is measured as a function of molding temperature. Companion tensile testing of macroscale Cu specimens was carried out at the corresponding molding temperatures. Microstructures of tensile tested macroscale Cu specimens and molded Cu specimens were characterized by combining focused ion beam (FIB) sectioning and imaging with ion-induced secondary electrons (ISEs). At all temperatures tested, measured tensile stress–strain curves for Cu show clear evidence for the occurrence of dynamic recrystallization (DRX) within macroscale tensile specimens. Additional FIB sectioning and imaging with ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322244 Wed, 13 Jan 2010 00:00:00 +0100 3322244 http://www.medworm.com/index.php?rid=3322242&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009069%2Fabstract%3Frss%3Dyes Abstract: In order to understand the origin of the residual stress state in thin films and its thickness dependence, the structure–stress relation of magnetron-sputtered Cr and CrN layers with thicknesses ranging from 100nm to 3μm was investigated in detail. Based on correlations between the layer-thickness-dependent grain size, texture and morphology and the magnitude of the intrinsic and thermal components of the residual stress, a model is proposed that explains the origin of internal stresses of thin polycrystalline films with zone T structures. The model was further extended for the CrN/Cr dual-layer system, where the CrN top layer is epitaxially aligned with the underlying highly (200)-oriented Cr interlayer. It is shown for the first time that both the intrinsic and thermal stres... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322242 Wed, 13 Jan 2010 00:00:00 +0100 3322242 http://www.medworm.com/index.php?rid=3322241&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009057%2Fabstract%3Frss%3Dyes Abstract: Strain in a deformation-twinned nanocrystalline Pd sample of about 24nm grain size was mapped by means of geometric phase analysis based on an individual high-resolution transmission electron microscopy image. The in-plane components of the strain tensor were calculated and charted. Strains with magnitudes of about 0.8% were found in the grain interior. Twins and matrix were significantly distorted relative to each other (by about 3° on average) and showed a strong rotation gradient from top to bottom, revealing that the whole grain is bent. An estimate of the strain energy stored in the Pd grain yielded a value of . Based on the strain distribution observed, a temporal deformation scenario has been developed. In our judgement, deformation twins had formed first and subsequently... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322241 Wed, 13 Jan 2010 00:00:00 +0100 3322241 http://www.medworm.com/index.php?rid=3322228&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008829%2Fabstract%3Frss%3Dyes Abstract: Phase separation phenomena in metallic glass systems have been explored by thermodynamic calculation and experimental method in the present study. Miscibility gap and spinodal curve for liquid phase in Gd–Ti–Al–Co/Cu systems have been calculated using the CALPHAD method. Based on the calculation result, various types of phase separation phenomena have been observed experimentally. Basically two types of structure are observed: interconnected-type structure by spinodal decomposition; and droplet-type structure by nucleation and growth mechanism. Multi-step phase separation occurs during cooling from the liquid, forming a hierarchical length scale composite structure. Depending on the glass-forming ability of the separated liquid phase, amorphous/amorphous or amorphous/crysta... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322228 Wed, 13 Jan 2010 00:00:00 +0100 3322228 http://www.medworm.com/index.php?rid=3322236&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009008%2Fabstract%3Frss%3Dyes Abstract: In metal matrix composites, thermal stresses are relaxed by either interface debonding, crack propagation or dislocation motion. The present paper shows that in the case of a magnesium matrix, interface thermal stresses are relaxed by dislocation motion in the basal plane (001) of the hexagonal structure. Different specimens were processed by a gas pressure infiltration method and the metallic matrix was oriented with respect to the interface by the Bridgman technique. Mechanical spectroscopy experiments show that the damping as well as the evolution of the relative shear modulus depend strongly on the orientation of the basal plane. The results are in good agreement with the theoretical model. The calculations show that the orientation of the glide plane influences the coupling ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322236 Mon, 11 Jan 2010 00:00:00 +0100 3322236 http://www.medworm.com/index.php?rid=3322210&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900857X%2Fabstract%3Frss%3Dyes Abstract: Aluminium/alumina composites based on ceramic preforms prepared via freeze-casting are examined. Domains composed of alternating but also interpenetrating ceramic and metallic lamellae are observed. Single-domain samples were extracted from composites processed under different conditions. In situ scanning electron microscopy analyses were carried out to investigate the damage evolution under compressive load. The composite is strong and brittle when loaded along directions parallel to the freezing direction. When compressed in other directions, the behavior is controlled by the soft metal. The plastic anisotropy is less pronounced than theoretical predictions for laminates, which is explained by the presence of bridges between the ceramic lamellae. Coating the preform with Cu or ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322210 Mon, 11 Jan 2010 00:00:00 +0100 3322210 http://www.medworm.com/index.php?rid=3322237&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900901X%2Fabstract%3Frss%3Dyes Abstract: The effects of drawing on the structure and mechanical properties of a Co-based metallic glass under tension were thoroughly investigated. Surface changes induced by drawing, including removal of surface flaws, surface chemical homogenization and generation of compressive residual stress tend to increase the fracture strength, whilst open volumes created during drawing, particularly nano-voids, are likely to soften the wires. Initially, the surface changes are decisive factors, but as drawing proceeds, the open volumes gradually become dominant, yielding a maximum fracture strength in the wires with an area reduction ratio of 22%. Moreover, it was found that the fracture strength reliability was enhanced by the drawing, which is due not only to the surface perfection but also to ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322237 Thu, 07 Jan 2010 00:00:00 +0100 3322237 http://www.medworm.com/index.php?rid=3322235&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008994%2Fabstract%3Frss%3Dyes Abstract: The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100μm in width in the specimen deformed via ro... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322235 Thu, 07 Jan 2010 00:00:00 +0100 3322235 http://www.medworm.com/index.php?rid=3322234&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008982%2Fabstract%3Frss%3Dyes Abstract: The low-frequency damping (tanδ) of a strongly textured β-titanium shape memory alloy (SMA) was investigated by a dynamic mechanical analysis (DMA) in a tensile mode together with a tensile test and a crystallographic analysis of the transformation. In addition to the high background of tanδ in martensite, a broad tanδ peak with a relaxation-like character was found in the martensite phase similar to the Ti–Ni SMAs. There was a critical stress for the broad peak that corresponds to the stress to complete the martensite variant reorientation, whereas the high background of tanδ had no critical stress. This implies that the broad peak is generated through the long-range motion of twin boundaries. A guideline to estimate the orientation dependence of damping in textured SMAs ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322234 Thu, 07 Jan 2010 00:00:00 +0100 3322234 http://www.medworm.com/index.php?rid=3322232&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008969%2Fabstract%3Frss%3Dyes Abstract: Al–Sc and Al–Ti semi-infinite targets were impacted by high-speed projectiles with velocities of 0.8, 2 and 4kms−1, respectively. The results show that deep columned craters with hemispherical bottoms were formed in the Al–Ti target, while near-hemispheroidal or relatively shallower craters formed in the Al–Sc alloy. It is concluded that different microstructures of Al–Sc and Al–Ti alloys, including different grain sizes and secondary particles precipitated in the matrix, result in their having greatly different capabilities of resisting impact. Residual microstructures of different samples are further discussed. It is possible that, due to the very large amount of energy imported into the target by high-speed impact, secondary Al3Sc lost its coherency and consequen... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322232 Wed, 06 Jan 2010 00:00:00 +0100 3322232 http://www.medworm.com/index.php?rid=3322239&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409009033%2Fabstract%3Frss%3Dyes Abstract: Phase transformations in Pd-capped epitaxial yttrium films grown on (0001) sapphire substrates covered with a Ti buffer layer and hydrogenated for different times were studied using transmission electron microscopy (TEM). For short hydrogen charging times, the phase transformation from α-Y to β-YH2 is associated with the nucleation and growth of two orientational variants, which after coalescence form twin-related lamellae of the β-YH2 phase with twin interfaces parallel to the substrate plane. Shockley partial dislocations are present at the twin boundaries; their glides during phase transformation are responsible for the formation of the twin lamellae. Superlattice reflections were observed for β-YH2, and the existence of a new long-range ordered superstoichiometric YH2+x p... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322239 Mon, 04 Jan 2010 00:00:00 +0100 3322239 http://www.medworm.com/index.php?rid=3322233&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008970%2Fabstract%3Frss%3Dyes Abstract: Grain growth and particle coarsening in Al–3.5Cu at a temperature of 450°C has been studied. Plastic deformation of this Zener-pinned system at strain rates of 10−3 and 10−4s−1 led to an increase in both the grain growth and particle coarsening rates. The results of mechanical tests and metallography, including in situ studies, showed that the material was deforming primarily by intragranular slip. The dynamic grain growth was ascribed to the geometric effect of deformation on the Zener pinning, and the rate sensitivity of the growth to the dynamic particle coarsening. The principal effect of deformation on particle coarsening was concluded to be increased diffusion due to the dislocation content. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322233 Mon, 04 Jan 2010 00:00:00 +0100 3322233 http://www.medworm.com/index.php?rid=3322231&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008957%2Fabstract%3Frss%3Dyes Abstract: We have successfully applied a hydrogen metallurgy synthesis to yield LaMg12−x intermetallic at 500°C. During a vacuum thermal desorption from the LaH3–MgH2 nanocomposite prepared by reactive ball milling in H2, hydrogen desorption from the La dihydride occurred via a mechanism of cooperative phase transformation at temperatures being 400° lower than the desorption from pure LaH2. The crystal structure of the intermetallic was determined by synchrotron X-ray diffraction (SR XRD). The orthorhombic LaMg12−x has a giant unit cell, the volume of which exceeds 8000Å3. In situ SR XRD studies showed the fine details of the hydrogen desorption process with several parallel and consecutive transformation steps. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322231 Mon, 04 Jan 2010 00:00:00 +0100 3322231 http://www.medworm.com/index.php?rid=3322230&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008842%2Fabstract%3Frss%3Dyes Abstract: The Young’s modulus (E), hardness (H) and fracture toughness (KIC) of various compositions of gadolinia doped-ceria (GDC, GdxCe1−xO2−x/2, 0.1⩽x⩽0.2) and yttria-stabilized zirconia (YSZ, Y0.08Zr0.92O1.96) electrolytes were investigated by nanoindentation. All samples were produced by the sol–gel method, formed by uniaxial pressure and sintered at 1400°C. In order to determine the mechanical properties, a Berkovich diamond tip was employed at applied loads of 5, 10, 30, 100 and 500mN. The results were interpreted by the Oliver–Pharr method and values of KIC were determined using the method of Palmqvist cracks. The residual imprints were observed by field emission scanning electron microscopy. The results obtained showed that the H, E and KIC of GDC decreased with inc... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322230 Mon, 04 Jan 2010 00:00:00 +0100 3322230 http://www.medworm.com/index.php?rid=3322229&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008830%2Fabstract%3Frss%3Dyes Abstract: 6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175MPa were investigated at 20kHz frequency, 50% of the oscillation amplitude, 34.5mms−1 sonotrode velocity and 20°C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state dislocation glide. Dynamic recovery is active in the upper and lower foils. Friction at the welding interface, instantaneous internal temperatures (0.5–0.8 of the melting temperature, Tm), contact pressure and fast strain rates result in transient microstructures and grain size reduction by continuous dynamic recrystallization (CDRX) within the bon... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322229 Mon, 04 Jan 2010 00:00:00 +0100 3322229 http://www.medworm.com/index.php?rid=3322227&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008817%2Fabstract%3Frss%3Dyes Abstract: Dislocation segments with Burgers vector b=〈100〉 are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b=1/2〈111〉. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight 〈100〉 edge dislocation is investigated here by atomic-scale computer simulation for α-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2〈111〉 fractional dislocations with atomic disregistry spread on p... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322227 Mon, 04 Jan 2010 00:00:00 +0100 3322227 http://www.medworm.com/index.php?rid=3322226&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008787%2Fabstract%3Frss%3Dyes Abstract: Although it is well known that Fe–Mn–C TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability o... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322226 Mon, 04 Jan 2010 00:00:00 +0100 3322226 http://www.medworm.com/index.php?rid=3322225&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008775%2Fabstract%3Frss%3Dyes Abstract: Face-centered-cubic thin films often have mixed (111)/(100) fiber texture. These orientations can have very different in-plane stiffnesses, leading to the possibility of significant stress inhomogeneities. Previous X-ray studies appeared to confirm this, reporting much higher stresses in (111)- than (100)-oriented grains. In those studies, the stress in the film normal direction was assumed to be zero everywhere, but Poisson effects suggest that out-of-plane stresses may be significant. Here, an X-ray data analysis that allows for out-of-plane stresses is presented and applied to X-ray data taken from a Cu film. The in-plane stress is shown to be homogeneous, and significant out-of-plane stresses arise. This analysis is shown to be more accurate and more consistent with the micro... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322225 Mon, 04 Jan 2010 00:00:00 +0100 3322225 http://www.medworm.com/index.php?rid=3322222&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900874X%2Fabstract%3Frss%3Dyes Abstract: In contrast to most nanostructured materials, outstanding mechanical property has been demonstrated in a nanostructured metastable austenitic steel, owing to the new characteristics of deformation-induced martensitic transformation. In this paper, by employing an in situ high-energy X-ray diffraction technique, we explore these characteristics by examining factors from the load partitioning, Lüders banding, to texture development. It was found that the martensitic transformation was mainly driven through Lüders band propagation. Marked load transfer takes place from austenite to martensite as Lüders band propagates, and continues into the homogeneous deformation regime. The texture development is mostly contributed by martensitic transformation, but dislocation-based plasticit... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322222 Mon, 04 Jan 2010 00:00:00 +0100 3322222 http://www.medworm.com/index.php?rid=3322223&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008751%2Fabstract%3Frss%3Dyes Abstract: The effect of a high magnetic field on the morphology and preferred orientation relationship of the Al–Al3Ni fiber eutectic has been investigated during directional solidification. Results indicate that an application of a high magnetic field has decreased the eutectic spacing and caused the appearance of the band-like structure. Moreover, it has been found that a high magnetic field has changed the preferred orientation relationship of the Al–Al3Ni eutectic. Indeed, the application of a 12T high magnetic field has caused the preferred orientation relationship of the Al{331}//Al3Ni{001}; Al [110]//Al3Ni[010] in the case of no magnetic field to transfer into the Al{001}//Al3Ni{102}; Al[102]// Al3Ni[010]. Further, in order to investigate the nucleation and growing mechanism of ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322223 Thu, 31 Dec 2009 00:00:00 +0100 3322223 http://www.medworm.com/index.php?rid=3322221&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008738%2Fabstract%3Frss%3Dyes Abstract: In situ observations of phase transformations involving melts are performed using energy-dispersive diffraction of synchrotron X-rays on electromagnetically levitated γ-TiAl alloys containing Nb. The determined primary solidification modes, confirmed by microstructure analysis, delivered new reliable data about the boundary of the α(Ti) solidification domain, which differs in the various Ti–Al–Nb phase diagram descriptions. These data have been used for a reassessment of the thermodynamic database of the ternary Ti–Al–Nb system. The new description realistically reflects the experimental findings. Liquidus and solidus temperatures determined by the pyrometric method agree fairly well with the calculated values. Direct experimental information on the nature of the reacti... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322221 Thu, 31 Dec 2009 00:00:00 +0100 3322221 http://www.medworm.com/index.php?rid=3322220&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008726%2Fabstract%3Frss%3Dyes Abstract: Samples of Ti–4.3Fe–6.7Mo–1.5Al were isothermally annealed in the temperature range of 730–780°C for various times to study the β–α transformation. Serial sectioning in conjunction with both optical and EBSD analyses was applied to determine the three-dimensional (3-D) morphologies of primary α phase. The 3-D analysis proved to be essential for characterization of the complex morphologies of α grains and consequently for the identification of growth behavior. It showed that nucleation of α grains takes place at β–β grain boundaries and significant branching takes place after initial growth of α grains along β–β grain boundaries. Some branches grow inside the β grain interior. The branching behavior is shown to interact with β–β grain boundaries, lead... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322220 Thu, 31 Dec 2009 00:00:00 +0100 3322220 http://www.medworm.com/index.php?rid=3322213&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008611%2Fabstract%3Frss%3Dyes Abstract: Due to their high aspect ratio, magnetic nanowires are interesting for various applications. Fe nanowires are of particular interest due to their high magnetization, which suggests high shape anisotropy is possible. Here, we show how the electrodeposition process can be adapted to the constraints of a high aspect ratio template in order to approach an ideal behaviour of smooth and pure Fe nanowires. An adjustment of the Fe2+ concentration and the addition of H3BO3 result in smooth and continuous nanowires; saturation polarization is achieved, together with an anisotropy field of up to 70% compared to pure Fe. Mössbauer spectroscopy reveals a negligible amount of impurities. Together with magnetic measurements we show that shape anisotropy aligns the preferential magnetization ax... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322213 Thu, 31 Dec 2009 00:00:00 +0100 3322213 http://www.medworm.com/index.php?rid=3129350&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008891%2Fabstract%3Frss%3Dyes (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3129350 Wed, 30 Dec 2009 16:21:32 +0100 3129350 http://www.medworm.com/index.php?rid=3322224&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008763%2Fabstract%3Frss%3Dyes Abstract: Novel wedge-geometry, dual-layer alumina samples, both undoped and 500ppm Y3+-doped, were studied in the temperature regime 1250–1400°C to determine the effect of Y3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322224 Wed, 30 Dec 2009 00:00:00 +0100 3322224 http://www.medworm.com/index.php?rid=3322219&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008714%2Fabstract%3Frss%3Dyes Abstract: Cluster dynamics is often used in the multi-scale procedure to link atomistic and macroscopic approaches, in particular when modelling precipitation processes. To extend its use to concentrated alloys, it is necessary to take into account accurately the exclusion zones and their overlap. By investigating the one-dimensional case, one obtains an exact formula for these zones, and its generalization to higher dimensions is proposed. By integrating cluster fragmentation/coagulation processes into cluster dynamics equations, a perfect agreement between atomistic simulations (Kinetic Monte Carlo) and cluster dynamics is reached on the whole range of concentrations for kinetics which govern microstructure in one dimension. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322219 Mon, 28 Dec 2009 00:00:00 +0100 3322219 http://www.medworm.com/index.php?rid=3322217&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008659%2Fabstract%3Frss%3Dyes Abstract: Slight deviations from the Kurdjumov–Sachs orientation relationship (KS OR) are often observed in the face-centered-cubic/body-centered-cubic (fcc/bcc) transformation systems, and some can be explained on the premise of the parallelism of either the close-packed planes (CPPs) or the close-packed directions (CPDs), as suggested in many models. This work investigates a new OR which deviates from the KS OR in both the CPPs and the CPDs. This OR is determined by requiring the habit plane to contain a single set of periodic dislocations along the invariant line lying in the CPPs. The angles of the double deviation, as a function of the lattice parameter ratio, are proved to be identical. The calculated results for a stainless steel are in good agreement with the experimental observa... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322217 Mon, 28 Dec 2009 00:00:00 +0100 3322217 http://www.medworm.com/index.php?rid=3322214&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008623%2Fabstract%3Frss%3Dyes Abstract: The extremely slow transformation kinetics of a nanocrystalline bainitic steel allows the carbon content of the bainitic ferrite away from any carbon-enriched regions such as dislocations and boundaries to be determined by atom probe tomography as the bainite transformation progresses at 200°C. A high level of carbon, well above that expected from para-equilibrium with austenite, has been detected in solid solution in bainitic ferrite at the early stage of transformation. Results provide strong evidence that bainite transformation is essentially displacive in nature so that the newly formed bainitic ferrite retains much of the carbon content of the parent austenite. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322214 Mon, 28 Dec 2009 00:00:00 +0100 3322214 http://www.medworm.com/index.php?rid=3322212&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900860X%2Fabstract%3Frss%3Dyes Abstract: Copper-based solid solutions with different contents of solute elements (Zn, Al, Ga, Sn, Ge) were deformed at room temperature and at liquid nitrogen temperature. The recrystallization behaviour of these alloys has been investigated by means of dynamic and isothermal measurements of the resistivity . Variations of from are interpreted in terms of changes in defect densities by recovery and recrystallization. Deviations from a linear temperature dependence of the resistivity increase with increasing solute concentration. This deviation (i.e. as determined at room temperature) also depends on the stacking fault energy . We observe a -dependency of which is also influenced by the deformation temperature. During deformation, controls the possibility of storing deformation energy in t... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322212 Mon, 28 Dec 2009 00:00:00 +0100 3322212 http://www.medworm.com/index.php?rid=3272846&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008544%2Fabstract%3Frss%3Dyes Abstract: The influence of a crystallographic symmetry break on the morphology of precipitates during the coherent precipitation of a trigonal phase in a close-packed hexagonal matrix is analyzed. It is pointed out that in spite of the isotropy of the stress-free strain of the precipitate in the basal plane, the existence of an extra elastic constant in the precipitate (associated to the loss of symmetry) induces a morphological evolution from a shape having a symmetry of revolution around the threefold axis to a needle-like one oriented along the compact directions in the basal plane. These general considerations are applied to the case of zirconium hydrides, the crystallography of which has recently been identified to be coherent with that of the αZr matrix. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272846 Mon, 28 Dec 2009 00:00:00 +0100 3272846 http://www.medworm.com/index.php?rid=3272843&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008519%2Fabstract%3Frss%3Dyes Abstract: The superelastic cyclic response of Ti74Nb26 shape memory alloy (SMA), and the nature of cyclic evolution of its superelastic properties and their unexpected static recovery process after cycling, were investigated at room temperature. The critical stress for stress-induced martensitic transformation (σSIM) and stress hysteresis (Δσ) continuously decrease with increasing number of superelastic cycles. However, cumulative irrecoverable strain during cycling in samples of particular processing conditions increases only up to a certain number of cycles before decreasing with further cycling. Stress-free aging at room temperature after cycling was shown to increase σSIM and Δσ. The unexpected room temperature recovery is attributed to the recovery of retained martensite and poi... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272843 Mon, 28 Dec 2009 00:00:00 +0100 3272843 http://www.medworm.com/index.php?rid=3322259&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008428%2Fabstract%3Frss%3Dyes The authors regret the misspelling of N. Moelans in Refs. . The name was listed as N. Moleans and it should have been N. Moelans. The corrections are listed below: (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322259 Fri, 25 Dec 2009 00:00:00 +0100 3322259 http://www.medworm.com/index.php?rid=3322218&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008702%2Fabstract%3Frss%3Dyes Abstract: A graded microstructure was produced in the surface layer of a pure Cu sample by means of surface mechanical attrition treatment (SMAT) [Wang K, Tao NR, Liu G, Lu J, Lu K. Acta Mater 2006;54:5281.]. The diffusion behavior of 63Ni in such a surface layer was investigated by the radiotracer technique at temperatures (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322218 Fri, 25 Dec 2009 00:00:00 +0100 3322218 http://www.medworm.com/index.php?rid=3322216&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008647%2Fabstract%3Frss%3Dyes Abstract: In situ nanomechanical tests are carried out to investigate the tensile and compressive behavior of 〈001〉-oriented body-centered cubic (bcc) metals W, Mo, Ta and Nb with nanometer dimensions. We find that the strength of these metals exhibits strong size dependence. The compressive size effect in Nb, as evaluated by the log–log slope of strength vs. nanopillar diameter, is −0.93, a factor of 2.1 greater than that for the other three metals W, Mo and Ta (−0.44). In tension, however, Ta and Nb show higher size effect slopes (−0.80 and −0.77) as compared with W and Mo (−0.58 and −0.43). We also report that while the yield strength of these metals is a strong function of size, the strain-hardening behavior does not present any size-dependent trends. We further discu... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322216 Fri, 25 Dec 2009 00:00:00 +0100 3322216 http://www.medworm.com/index.php?rid=3322215&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008635%2Fabstract%3Frss%3Dyes Abstract: An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1GPa) and unloading. Both macroscopic stress–strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322215 Fri, 25 Dec 2009 00:00:00 +0100 3322215 http://www.medworm.com/index.php?rid=3322211&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008593%2Fabstract%3Frss%3Dyes Abstract: This paper presents the results of sliding wear experiments conducted on high-purity titanium (Ti) against bearing-steel in liquid nitrogen (LN2; boiling point: 77K) environment. Ti samples of three different grain sizes (9, 17 and 37μm) were used to study the effect of hardness, derived from grain refinement as well as cryogenic test temperature, on the wear properties of Ti. In our experiments, a constant load of 10N and sliding speeds of 0.67, 1.11 and 4.19ms−1 were used. The coefficient of friction (COF) for this tribo-couple varied between ∼0.25 and ∼0.50. While a steady state was always achieved, a peak in the COF was always noted in case of coarse-grain (37μm) Ti tested at a sliding speed of 4.19ms−1. Under the investigated sliding conditions, the wear rate was f... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322211 Fri, 25 Dec 2009 00:00:00 +0100 3322211 http://www.medworm.com/index.php?rid=3272851&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008416%2Fabstract%3Frss%3Dyes The Authors regret that Fig. 3 is incorrectly labeled on p. 2922. It is currently labeled as: “12Zn–1.1Cu–.20Mn–.16Cr.” However, the alloy should be labeled as: “12Zn–1.1Cu–.29Mn–.02Cr”. The figure is accurate and the illustrative purpose of the figure as described is unchanged by the labeling error. The results, conclusions, and contribution of the research reported are not affected by this labeling error as all of the alloys in the investigation contained the presented structural precipitates. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272851 Fri, 25 Dec 2009 00:00:00 +0100 3272851 http://www.medworm.com/index.php?rid=3272849&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008581%2Fabstract%3Frss%3Dyes In this study it is shown that it is possible to adapt well-known ceramic processing strategies to the fabrication of thick lead zirconate titanate (PZT) films on Cu with useful ferroelectric properties. PZT powders with optimized particle sizes are used to fabricate thick films by electrophoretic deposition in combination with a post-deposition isostatic pressing step. This approach to maximize green packing is sufficient to dramatically lower the required sintering temperatures. 25μm thick PZT films on Cu sintered at 900°C have a dielectric permittivity of 585, a loss tangent at 10kHz of 0.03, a remanent polarization of 19μCcm−2 and a coercive field of 22kVcm−1. This significant improvement in the dielectric response opens the possibility of using thick PZT films on Cu for a wide ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272849 Fri, 25 Dec 2009 00:00:00 +0100 3272849 http://www.medworm.com/index.php?rid=3272848&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008568%2Fabstract%3Frss%3Dyes Abstract: The average rotations of 157 individual grains measured in an Al–0.1%Mn polycrystal deformed in hot plane-strain compression to a strain of 1.2 have been compared to the predictions from several crystal plasticity models. The Taylor model successfully predicts the distributions of the rotation angles, but overestimates the rate of evolution of the rotation axes, which explains the overestimation of the final texture. The model also provides a first-order agreement for the rotation axes and the final components of the individual grains. The discrepancies are related to the influence of grain interaction. The main mechanisms of texture development at the level of the individual grains are identified through an analysis of their orientation trajectories. The introduction of local ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272848 Fri, 25 Dec 2009 00:00:00 +0100 3272848 http://www.medworm.com/index.php?rid=3272847&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008556%2Fabstract%3Frss%3Dyes Abstract: Using in situ transmission electron microscopy, we studied the stability of growth twins. We observed the rapid migration of incoherent twin boundaries (ITBs), indicating that nanotwins are unstable. Topological analysis and atomistic simulations are adopted to explore detwinning mechanisms. The results show that: (i) the detwinning process is accomplished via the collective glide of multiple twinning dislocations that form an ITB; (ii) detwinning can easily occur for thin twins, and the driving force is mainly attributed to a variation of the excess energy of a coherent twin boundary; (iii) shear stresses enable ITBs to migrate easily, causing the motion of coherent twin boundaries; and (iv) the migration velocity depends on stacking fault energy. The results imply that detwinni... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272847 Fri, 25 Dec 2009 00:00:00 +0100 3272847 http://www.medworm.com/index.php?rid=3272845&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008532%2Fabstract%3Frss%3Dyes Abstract: Various constant magnitudes of through-thickness electric field are applied to a poled PZT wafer for about 1800s at four different high temperatures. The wafer is then removed swiftly from the field and kept at zero electric field for about 1000s. During the whole period of nonzero and zero electric field loading time, the electric displacement in thickness direction and the in-plane strain of the wafer are measured over time. The measured responses at different electric fields and temperatures are discussed and compared with one another. The dependence of various linear moduli on remanent quantities and temperature is obtained; the creep responses of the wafer at high temperatures are compared and discussed; and finally the domain-switching processes at different electric fields... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272845 Fri, 25 Dec 2009 00:00:00 +0100 3272845 http://www.medworm.com/index.php?rid=3272844&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008520%2Fabstract%3Frss%3Dyes We report a Monte Carlo simulation study of the molten Fe–C–S system with the aim of developing a theoretical understanding of the influence of sulphur during decarburization reactions in Fe–C alloys. Focussing specifically on the role played by free surfaces, computer simulations were based on the hexagonal atomistic model of Fe–C–S system using isotropic atomic interaction parameters; free surfaces were characterized by a missing layer of atoms. Three geometrical configurations, namely a liquid bath, a prismatic block and a spherical droplet, were investigated. Simulations were carried out as a function of melt carbon and sulphur concentration, temperatures and surface/volume ratios of the simulation cell. Sulphur atoms were found to preferentially concentrate in the top few la... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272844 Fri, 25 Dec 2009 00:00:00 +0100 3272844 http://www.medworm.com/index.php?rid=3272842&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008404%2Fabstract%3Frss%3Dyes Abstract: An optimization-based computational model is proposed to study domain evolution in polycrystalline ferroelastics composed of numerous randomly oriented grains, each of which consists of multiple types of domains. Under any prescribed loading, the volume fraction of each domain in a grain is obtained by minimizing the free energy of the said grain using an optimization method. The mechanical constraint from the neighboring grains is considered using Eshelby inclusion approach. This model has the similar superiority as the phase field model, which does not require imposition of any priori domain-switching criterion. The computational efficiency of this model is fairly high and it is feasible to study three-dimensional cases using numerous grains. Furthermore, this model can reprodu... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272842 Fri, 25 Dec 2009 00:00:00 +0100 3272842 http://www.medworm.com/index.php?rid=3272841&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008398%2Fabstract%3Frss%3Dyes Abstract: We performed atomistic simulations of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) to study the segregation of point defects near (100) surfaces. A hybrid Monte Carlo–molecular dynamics algorithm was developed to sample the equilibrium distributions of dopant cations and oxygen vacancies. The simulations predict an increase of dopant concentration near the surface, which is consistent with experimental observations. Oxygen vacancies are also found to segregate in the first anion layer beneath the surface and to be depleted in the subsequent anion layers. While the ionic size mismatch between dopant and host cations has been considered as a driving force for dopant segregation to the surface, our simulations show that the correlation between individual point ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272841 Fri, 25 Dec 2009 00:00:00 +0100 3272841 http://www.medworm.com/index.php?rid=3272829&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008271%2Fabstract%3Frss%3Dyes Abstract: This paper presents the results of a combined experimental and numerical investigation focused on the effects of an in process water cooling treatment aimed at improving the final quality of friction stir welded butt joints in terms of mechanical resistance and metallurgy of the processed material. Micro and macro observations, together with the evolution of an already developed finite element tool, have been used to analyze specimens obtained under different process conditions. Water cooling was found to enhance joint strength, reducing the material softening usually observed in the thermo-mechanically affected zone area, with no detrimental effect on nugget integrity. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272829 Fri, 25 Dec 2009 00:00:00 +0100 3272829 http://www.medworm.com/index.php?rid=3272840&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008386%2Fabstract%3Frss%3Dyes Abstract: First-principles calculations and experimental methods were employed to investigate the relative stability of intermetallic phases in the Cu–Zr system. Computed enthalpies of formation indicate that Cu51Zr14-β and CuZr2-C11b are stable phases, while Cu5Zr-C15b, Cu10Zr7-ϕ and CuZr-B2 are metastable at 0K. Heat treatment and microanalysis revealed two important findings which clarify the phase equilibria. First, the stability range for the Cu5Zr-C15b phase was found to have a lower bound associated with an eutectoid invariant between 802 and 955K, below which it decomposes to face-centered cubic Cu plus Cu51Zr14-β. Second, the Cu5Zr8 phase, previously reported as stable, was not observed in a Cu–56.4at.% Zr alloy after holding at 955 and 1036K for >100h. This phase, therefor... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272840 Wed, 23 Dec 2009 00:00:00 +0100 3272840 http://www.medworm.com/index.php?rid=3272831&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008295%2Fabstract%3Frss%3Dyes Abstract: This paper describes the use of non-linear ultrasonic techniques for the characterization of material degradation in 99.98% pure copper due to high-temperature creep. Flat dog-bone-shaped specimens were subjected to constant load creep testing at different stress and temperature levels. Creep damage progression was monitored by conducting continuous and interrupted mode creep tests. In the case of continuous loading non-linear ultrasonic (NLU) measurements were conducted after fracture at different locations along the gage length of the sample. For interrupted tests the NLU measurements were conducted on different creep life fractions, through periodic interruption of the creep test. In all cases a through transmission NLU measurement technique was employed. Three different non-l... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272831 Wed, 23 Dec 2009 00:00:00 +0100 3272831 http://www.medworm.com/index.php?rid=3272830&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008283%2Fabstract%3Frss%3Dyes Abstract: The dynamics of spreading of liquid metal atoms via molecular dynamics is considered vs. the commensurability of the solid surface with respect to the size of the liquid atoms. The solid surfaces are modeled as rigid (100) oriented Ni and, for two series of simulations, the lattice spacing of the substrate is varied from the regular equilibrium spacing to a commensurate situation with Au or Ag drops spreading spontaneously on top. The diffusion is calculated in the layered region of the liquid in contact with the two different solid surfaces and then compared. Then, the dynamic evolution of the contact angle is fitted to Molecular Kinetic Theory and compared with the two substrate geometries. It is observed that the friction parameter scales as the inverse of the diffusion in the... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272830 Wed, 23 Dec 2009 00:00:00 +0100 3272830 http://www.medworm.com/index.php?rid=3111237&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008477%2Fabstract%3Frss%3Dyes (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3111237 Tue, 22 Dec 2009 16:27:11 +0100 3111237 http://www.medworm.com/index.php?rid=3272839&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008374%2Fabstract%3Frss%3Dyes Abstract: The deformation of nanocrystalline aluminum was studied using molecular dynamics simulation at homologous temperatures up to 0.97. The microstructures and stress–strain response were examined in a polycrystalline and bicrystal configuration. The activation energies for dislocation-based deformation as well as grain boundary sliding and migration were quantified by fitting simulation data to temperature using an Arrhenius relation. The activation energy for the flow stress response suggests that deformation is largely accommodated by sliding and migration of grain boundaries. This is in agreement with simulated microstructures, indicating a negligible degree of dislocation interaction within each grain, and microstructural observations from high strain rate processes are also co... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272839 Mon, 21 Dec 2009 00:00:00 +0100 3272839 http://www.medworm.com/index.php?rid=3272837&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008350%2Fabstract%3Frss%3Dyes Abstract: A multi-phase field model for quantitative simulations of polycrystalline solidification of binary alloys is introduced. During the free-growth stage of solidification, the model exploits the thin-interface analysis developed by Karma [3] in order to realistically capture bulk phase diffusion and the sharp interface corrections predicted by traditional models of solidification. During grain boundary coalescence, the model is constructed to reproduce the properties of repulsive grain boundaries described by Rappaz et al. [29]. The model provides a very simple mechanism for decoupling of solute and concentration fields at steady state, an important feature for calculating grain boundary energies. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272837 Mon, 21 Dec 2009 00:00:00 +0100 3272837 http://www.medworm.com/index.php?rid=3272836&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008349%2Fabstract%3Frss%3Dyes Abstract: A new methodology is described for in situ characterization of fatigue damage accumulation using nonlinear ultrasonic measurements via analysis of the feedback signal of a closed-loop ultrasonic fatigue system. In the very high-cycle fatigue regime, ultrasonic nonlinearity increases with initiation and growth of a dominant, life-limiting fatigue crack. Based on the increase in the ultrasonic nonlinearity with fatigue cycling, crack initiation, small fatigue crack growth and fast crack growth regimes have been distinguished during cycling in specimens with different pore sizes tested at various stress amplitudes. The fraction of fatigue life spent in initiation of a life-limiting fatigue crack decreases with increasing stress amplitude. For a constant stress amplitude, the initiat... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272836 Mon, 21 Dec 2009 00:00:00 +0100 3272836 http://www.medworm.com/index.php?rid=3272835&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008337%2Fabstract%3Frss%3Dyes Abstract: Multiphase Mo–Si–B alloys containing a Mo solid solution matrix and brittle Mo3Si and Mo5SiB2 (T2) intermetallic phases are candidates for ultra-high-temperature applications. The elevated temperature uniaxial tensile response at a nominal strain rate of 10−4 s–1 and the tensile creep response at constant load between 1000°C and 1300°C of a (i) single phase solid solution (Mo–3.0Si–1.3B in at.%), (ii) two-phase alloy containing ∼35 vol.% T2 phase (Mo–6Si–8B in at.%) and (iii) three-phase alloy with ∼50 vol.% T2+Mo3Si phases (Mo–8.6Si–8.7B in at.%) were evaluated. The results confirm that Si in solid solution significantly enhances both the yield strength and the creep resistance of these materials. A Larson–Miller plot of the creep data showed improved... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272835 Mon, 21 Dec 2009 00:00:00 +0100 3272835 http://www.medworm.com/index.php?rid=3272833&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008313%2Fabstract%3Frss%3Dyes Abstract: The electric-field-induced strain behavior in (1−x−y)(Bi0.5Na0.5)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 electroceramics has been studied using a combinatorial technique. A stoichiometrically graded sample was produced to contain compositions across the ternary phase diagram between the two end-member components of 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 and 0.86(Bi0.5Na0.5)TiO3–0.14(K0.5Na0.5)NbO3. Both composition and structural information were measured simultaneously during the application of electric fields using secondary X-ray fluorescence and high-energy X-ray microdiffraction, respectively. An initial electric-field-induced distortion from the pseudo-cubic structure is seen across all compositions, while those with a greater concentration of BaTiO3 also undergo an electric-fie... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272833 Mon, 21 Dec 2009 00:00:00 +0100 3272833 http://www.medworm.com/index.php?rid=3272823&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008210%2Fabstract%3Frss%3Dyes Abstract: An extensive investigation of the lattice expansion (up to 1200°C) of porous synthetic cordierite (obtained by firing a mixture of talc, clay, alumina and silica) was carried out using time-of-flight neutron diffraction at LANSCE, Los Alamos, NM, USA and FNLP, Dubna, Russia. An extruded rod and several powders, with different particle size (dispersity), were studied, with the aim of monitoring the variation of the (lattice) micro-strain as a function of temperature and its influence on the microscopic and macroscopic thermal expansion. Results show a different expansion of the a- and b-axes of the orthorhombic cell (in the rod above 800°C). While the finest powder seems to contract more along the c-axis, thus hinting at the presence of smaller stress, the integral peak width in... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272823 Mon, 21 Dec 2009 00:00:00 +0100 3272823 http://www.medworm.com/index.php?rid=3272838&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008362%2Fabstract%3Frss%3Dyes Abstract: Hydrogen-etching of 6H–SiC(0001) substrates removed mechanical polishing damage and produced an array of parallel, unit cell high steps. The initial stage of AlN deposition on these etched substrates occurred via island nucleation, both on step edges and on terraces. Coalesced AlN films did not show scratch-induced undulations observed on the surfaces of AlN films deposited on as-received substrates. The films also had a lower density of growth pits. The majority of threading dislocations (TDs) observed in these films were of a type. Jagged networks of misfit dislocations were seen on the terraces in the 15nm thick AlN/hydrogen-etched SiC composite. GaN islands nucleated primarily at undulations in AlN layers and at hillocks on the AlN surface of as-received and hydrogen-etched... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272838 Fri, 18 Dec 2009 00:00:00 +0100 3272838 http://www.medworm.com/index.php?rid=3272834&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008325%2Fabstract%3Frss%3Dyes Abstract: Equal-channel angular pressing (ECAP) is an established method to produce ultra-fine-grained (UFG) materials with extraordinary mechanical properties. However, different methods to characterize the complex microstructure give contradictory results. Therefore an ECAP-processed UFG aluminum alloy AA6063 was characterized by various electron-microscopy-based methods such as backscattered electron contrast, electron backscatter diffraction, transmission electron microscopy and low-voltage scanning transmission electron microscopy. Only a skilful combination of all methods reveals the complete information about the microstructure which is needed to understand the results of the mechanical testing by nanoindentation, tensile tests and strain-rate jump test. The main difference is the a... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272834 Fri, 18 Dec 2009 00:00:00 +0100 3272834 http://www.medworm.com/index.php?rid=3272828&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900826X%2Fabstract%3Frss%3Dyes Abstract: Molecular dynamics (MD) within the framework of the embedded atom method and the first-principles discrete variational method (DVM) are both used to study the effect of Re in the γ phase, the phase and the interface of Ni-based single-crystal superalloys. From the MD relaxation it is found that the interface only has two atomic configurations, i.e. a coherent region and a misfit dislocation region, and the “cage-like” misfit dislocation networks, consist of {001} edge dislocations winding over the precipitate phase. The MD results also show that the substitution atom Re stabilizes both the γ phase and the phase, and influences the degree of mismatch between γ and . From the simulation results we find that Re atoms have a tendency to cluster in both the γ phase and the pha... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272828 Fri, 18 Dec 2009 00:00:00 +0100 3272828 http://www.medworm.com/index.php?rid=3272832&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008301%2Fabstract%3Frss%3Dyes Abstract: Internal oxidation experiments under different oxidation conditions focusing on the characteristics of noble metal exudation are presented together with finite element method (FEM) simulation calculations of the build-up of internal stresses. In a high-temperature bending test with a fully oxidized Ag–SnO2–In2O3 sample stress states that were comparable with those occurring during internal oxidation were generated, but exudation of Ag was not observed. From further targeted internal oxidation experiments in combination with FEM simulation calculations of internal stress distributions it can be concluded that internal stresses play a minor role in the occurrence of noble metal exudation. It is suggested that exudation occurs due to a gradient in the chemical potential of the n... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272832 Thu, 17 Dec 2009 00:00:00 +0100 3272832 http://www.medworm.com/index.php?rid=3272827&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008258%2Fabstract%3Frss%3Dyes Abstract: The behavior of aluminum/silicon carbide nanolayered composite in response to nanoindentation loading is studied. The effects of heterogeneity on the deformation fields, as well as the hardness and elastic modulus obtained from indentation, are investigated using finite element analysis. Attention is also devoted to correlating the numerical results with experimental deformation and damage features. The model uses an explicit layered structure within the axisymmetric framework. It is found that the nanolayered composite results in unique deformation patterns. Significant tensile stresses can be generated locally along certain directions, which offers a mechanistic rationale for the internal cracking observed experimentally. The unloading process also leads to an expansion of the ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272827 Thu, 17 Dec 2009 00:00:00 +0100 3272827 http://www.medworm.com/index.php?rid=3212140&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008015%2Fabstract%3Frss%3Dyes Abstract: Reactive ball milling and annealing is proposed as a new production method for oxide dispersion strengthened (ODS) steels. A highly concentrated Fe–38atm.% Y2O3 ODS model alloy was processed by reactive ball milling and annealing of YFe3 and Fe2O3 powders so as to induce the chemical reaction 2YFe3+Fe2O3 → 8Fe+Y2O3. The model alloy was characterised after milling and annealing by complementary techniques, including atom probe tomography. Ball milling up to the stationary state results in the formation of two metastable nanometric interconnected phases: super-saturated α-iron and an yttrium and oxygen rich phase. Annealing leads the system towards equilibrium through: (i) a chemical evolution of each phase to nearly pure α-Fe and Y2O3 oxide slightly sub-stoichiometric in oxy... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212140 Thu, 17 Dec 2009 00:00:00 +0100 3212140 http://www.medworm.com/index.php?rid=3272826&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008246%2Fabstract%3Frss%3Dyes Abstract: The non-isothermal decomposition of austenite into ferrite and pearlite in Fe–xC–1.5 wt.% Mn steels with x=0.1, 0.2 and 0.3 wt.% C is investigated by in situ dilatometry and microstructure characterization in magnetic fields up to 16T. The global shift towards higher temperatures of the respective austenite, ferrite+austenite and ferrite+pearlite stability regions is experimentally quantified. A systematic increase in the ferrite area fraction and proportional reduction of the Vickers hardness values with the magnetic field intensity are also reported. Moreover, the steels’ magnetizations, measured up to 3.5T and 1100K, are used to calculate the magnetic contribution to the free energy of the transformation and to account thermodynamically for the field dependence of the tr... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272826 Wed, 16 Dec 2009 00:00:00 +0100 3272826 http://www.medworm.com/index.php?rid=3272825&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008234%2Fabstract%3Frss%3Dyes Abstract: It has been demonstrated that the strength of an Al–Si–Cu alloy is maximized by high-temperature solution treatment at 807K, which is approximately 16K higher than the ternary eutectic temperature. The dual-energy K-edge subtraction imaging technique has been employed to obtain the spatial distribution of copper and its change during its solution treatment in three dimensions quantitatively, providing interpretations of the improved mechanical properties in terms of age-hardenability and its spatial variation. It has been also confirmed that the occurrence of incipient local melting and the accompanying growth of micro pores adjacent to the melt regions lead to fractures caused by these defects. However, it can be inferred that the positive effects can outweigh the negative e... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272825 Mon, 14 Dec 2009 00:00:00 +0100 3272825 http://www.medworm.com/index.php?rid=3272819&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008179%2Fabstract%3Frss%3Dyes Abstract: The partitioning of platinum group metal (PGM) additions in polycrystalline Ni-base superalloys has been investigated. Alloys with a baseline composition of 15Al–5Cr–1Re–2Ta–0.1Hf (at.%) with systematic variations in Pt, Ir, Ru and W were cast and heat-treated to produce bimodal two-phase γ–γ′ microstructures. Electron microprobe analysis was used to measure the composition of coarse γ′ particles. Selected alloys were studied using atom probe tomography. Pt and Ru weakly partition to the γ′ and γ phases, respectively, whereas Ir partitions equally between both phases. Pt and Ru do not change partitioning behavior appreciably with additional W and Re. Interestingly, Ir lowers γ′ volume fraction and reduces partitioning of W, Re, Ru, Al and Pt. Tungsten part... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272819 Mon, 14 Dec 2009 00:00:00 +0100 3272819 http://www.medworm.com/index.php?rid=3212147&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008106%2Fabstract%3Frss%3Dyes Abstract: Single crystalline copper beams with thicknesses between 0.7 and 5μm are manufactured with a focused ion beam technique and bent in a nanoindenter. The yield strengths of the beams show a mechanical size effect (smaller-is-stronger). The geometrically necessary dislocation (GND) densities estimated from misorientation maps do not explain the observed size effect. Also, accumulation of GNDs principally requires pre-straining. We hence introduce a mean-field breakdown theory and generalize it to small-scale mechanical tests other than bending. The mean-field breakdown limit is defined in terms of a microstructural correlation measure (characteristic dislocation bow-out length) below which the local availability of dislocation sources and not the density of GNDs dominates the mecha... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212147 Fri, 11 Dec 2009 00:00:00 +0100 3212147 http://www.medworm.com/index.php?rid=3272822&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008209%2Fabstract%3Frss%3Dyes Abstract: Self- and impurity diffusivities in body-centered-cubic (bcc) iron have been calculated within the formalisms of harmonic transition-state theory and the Le Claire nine-frequency model for vacancy-mediated diffusion. The approach combines first-principles calculations of vacancy formation, migration, and solute-binding enthalpies and entropies in the ferromagnetic phase, with an empirical relationship for the effect of magnetic disorder on diffusion activation energies. Calculated Fe self-diffusion and Mo and W impurity-diffusion coefficients are shown to agree within a factor of five with the most recent experimental measurements in both the ferromagnetic and paramagnetic phases. Calculated diffusion coefficients for Mo and W impurities are comparable to or larger than that for ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272822 Thu, 10 Dec 2009 00:00:00 +0100 3272822 http://www.medworm.com/index.php?rid=3272821&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008192%2Fabstract%3Frss%3Dyes Abstract: The effect of gaseous hydrogen on cyclic slip behavior around a fatigue crack tip introduced along the {110} plane in a Fe–3.2wt.% Si alloy is precisely investigated by cross-sectional transmission electron microscopy and fractography. The results clearly suggest that the fatigue crack growth rate is promoted by hydrogen, whereas the number of dislocations emitted per load cycle is reduced. In addition, dislocation distribution is localized around the crack, causing quasi-brittle crack morphology. A sustained load test confirms that no subcritical crack growth caused by cleavage or micro-void coalescence exists along the {110} plane, which indicates that the observed increase in the fatigue crack growth rate is correlated solely to the intrinsic effect of hydrogen on the cyclic... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272821 Thu, 10 Dec 2009 00:00:00 +0100 3272821 http://www.medworm.com/index.php?rid=3272820&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008180%2Fabstract%3Frss%3Dyes Abstract: Molecular dynamics simulations with the Tersoff potential were used to study the response of twinned SiC nanowires under tensile and compressive strain. The critical strain of the twinned nanowires can be enhanced by twin stacking faults, and their critical strains are larger than those of perfect nanowires with the same diameters. Under axial tensile strain, the bonds of the nanowires are stretched just before failure. The failure behavior is found to depend on the twin segment thickness and the diameter of the nanowires. An atomic chain is observed for thin nanowires with small twin segment thickness under tension strain. Under axial compressive strain, the collapse of twinned SiC nanowires exhibits two different failure modes, depending on the length and diameter of the nanowi... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272820 Thu, 10 Dec 2009 00:00:00 +0100 3272820 http://www.medworm.com/index.php?rid=3272817&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008155%2Fabstract%3Frss%3Dyes Abstract: Data on anisotropy of grain boundary properties are frequently published. In some cases, when they show the reverse course of structural dependence than is expected, they can seem confusing. Examples of this “reversed anisotropy” found for grain boundary segregation, diffusion and migration are presented. We demonstrate that the reversed anisotropy of grain boundary properties is caused by the compensation effect. This can have serious consequences for grain boundary engineering. It is also suggested that grain boundaries can be classified specifically and generally solely on the basis of well-defined thermodynamic parameters. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272817 Thu, 10 Dec 2009 00:00:00 +0100 3272817 http://www.medworm.com/index.php?rid=3212146&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900809X%2Fabstract%3Frss%3Dyes Abstract: Vanadium samples with controlled oxygen impurity of up to 2460at.ppm were irradiated with fast neutrons to a fluency of at 150°C. The irradiation-induced nanovoids and the interaction between the defects and the oxygen impurities are studied systematically by combining the positron lifetime technique, the coincidence Doppler broadening technique and the first-principles calculations. The nanovoids are seen to be decorated with the oxygen impurities, which play a significant role in the dynamic processes of the formation of the nanovoids by irradiation and their subsequent recovery by post-irradiation annealing. The decoration with oxygen impurities not only enhances the nanovoid formation but also stabilizes them during low-temperature annealing ( (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212146 Thu, 10 Dec 2009 00:00:00 +0100 3212146 http://www.medworm.com/index.php?rid=3212145&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008088%2Fabstract%3Frss%3Dyes Abstract: Elastomer films with three-dimensional features self-organized into coherent and semi-coherent buckling domains were created by implanting different species of metal ions and combinations thereof, using a metal evaporation ion source, into quality polydimethylsiloxane films. As a result of the implantation process, functionalized discrete regions of strain-induced surface buckling were created, taking the forms of domains of parallel surface waves, semi-ordered regions and disordered regions. In addition, deep, strain-induced, V-shaped cracks were observed to penetrate well into the elastomer matrix. Characterization was via optical microscopy, X-ray diffraction, atomic force microscopy and high-resolution scanning electron microscopy (SEM) in the form of field emission SEM. It w... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212145 Thu, 10 Dec 2009 00:00:00 +0100 3212145 http://www.medworm.com/index.php?rid=3212143&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008064%2Fabstract%3Frss%3Dyes Abstract: Hard X-ray diffraction experiments have provided evidence of a strongly heterogeneous distribution of dislocation densities along the axis of cylindrical ice single crystals oriented for basal slip in torsion creep. The dislocation arrangements showed a complex scale-invariant character, which was analyzed by means of statistical and multifractal techniques. A trend to decreasing autocorrelation of the dislocation distribution was observed as deformation proceeds. At low strain levels, long-range spatial correlations control the distribution, but short-range correlations in relation with cross-slip progressively prevail when strain increases. This trend was reproduced by a model based on field dislocation dynamics, a theory accounting for both long-range elastic interactions and ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212143 Thu, 10 Dec 2009 00:00:00 +0100 3212143 http://www.medworm.com/index.php?rid=3272850&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008027%2Fabstract%3Frss%3Dyes The authors regret that a presents an unphysical schematic temperature dependence of the length change. The corrected figure is given below. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272850 Wed, 09 Dec 2009 00:00:00 +0100 3272850 http://www.medworm.com/index.php?rid=3272824&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008222%2Fabstract%3Frss%3Dyes Abstract: The Poisson’s ratio of Zr-based bulk metallic glasses in the system Zr63−xCu24AlxNi10Co3 was found to exhibit a non-monotonous behavior as a function of x when measured with ultrasound by the pulse–echo technique. In addition, from wave propagation velocity measurements at different frequencies, i.e. f=2.25MHz and f=10MHz, a composition-dependent anelastic behavior as a function of x is found, exhibiting a similar non-monotonous behavior. In this work we further investigated the plastic deformation and the creep properties of this glass system in compression tests and by nanoindentation. The plastic strain and the measured creep deformation show correlations with the Poisson’s ratio. We then discuss the anelastic behavior observed while measuring the sound-wave propagatio... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272824 Wed, 09 Dec 2009 00:00:00 +0100 3272824 http://www.medworm.com/index.php?rid=3272816&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008143%2Fabstract%3Frss%3Dyes Abstract: Macroscopic shrinkage in sintering is described as a linear function of the sintering stress tensor and the viscosity tensor, which is determined by taking into account the grain boundary diffusion mechanism and the anisotropy in the microstructure. For a simple orthorhombic structure in equilibrium, the anisotropic shrinkage rate is dominated by the deviatoric component of the viscosity tensor, which is approximately proportional to the logarithm of the aspect ratio of a volume element, and acts so as to deform the elongated structure to be more isotropic. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272816 Wed, 09 Dec 2009 00:00:00 +0100 3272816 http://www.medworm.com/index.php?rid=3212148&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008118%2Fabstract%3Frss%3Dyes Abstract: Intermetallic, γ-TiAl, equiaxed, small-grain (∼2μm) structures with lamellar γ/α2-Ti3Al colonies with average spacing of 0.6μm have been fabricated by additive manufacturing using electron beam melting (EBM) of precursor, atomized powder. The residual microindentation (Vickers) hardness (HV) averaged 4.1GPa, corresponding to a nominal yield strength of ∼1.4GPa (∼HV/3), and a specific yield strength of 0.37GPacm3g−1 (for a density of 3.76gcm−3), in contrast to 0.27GPacm3g−1 for EBM-fabricated Ti–6Al–4V components. These results demonstrate the potential to fabricate near net shape and complex titanium aluminide products directly using EBM technology in important aerospace and automotive applications. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212148 Wed, 09 Dec 2009 00:00:00 +0100 3212148 http://www.medworm.com/index.php?rid=3322209&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900812X%2Fabstract%3Frss%3Dyes Abstract: The intrinsic brittleness and ductility of intergranular fracture along a number of symmetrical [110] tilt grain boundaries (GBs) in Cu are investigated via combined atomistic and continuum studies of dislocation nucleation from an atomically sharp crack tip. In all cases investigated, the classical model of Rice predicts a directional anisotropy in that, along a given GB, brittle cleavage is favored for crack propagation in one direction while dislocation emission from the crack tip is preferred in the opposite direction. This prediction is validated by atomistic simulations of crack propagation along coherent GBs, including and . However, for incoherent GBs such as and , such directional anisotropy in intrinsic ductility is not observed; instead, we show that dislocation emissi... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3322209 Mon, 07 Dec 2009 00:00:00 +0100 3322209 http://www.medworm.com/index.php?rid=3272818&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008167%2Fabstract%3Frss%3Dyes Abstract: The anisotropic mechanical response of single-crystal nickel-based superalloys is simulated. At 1123K, two uniaxial tensile loading cases are simulated: one along [001] and another along [111]. Resulting stress–strain curves, stress distributions, interfacial dislocation structures are analysed. In accordance with experiments, the simulations show an anisotropic yield strength. The applied strain is accommodated by dislocations propagating through matrix channels on octahedral slip systems. The net result appears as slip bands along the cubic directions, even though no cubic slip systems are activated. In the [001] case, the plastic flow is distributed more or less evenly among the three matrix channels, whereas in the [111] case it is mainly concentrated in one single channel.... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272818 Mon, 07 Dec 2009 00:00:00 +0100 3272818 http://www.medworm.com/index.php?rid=3272815&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008131%2Fabstract%3Frss%3Dyes Abstract: The plastic deformation of two classes of fine-grained aluminium alloys at elevated temperatures and slow strain rates have been investigated. One class of material, Al–Cu–Zr, was processed to develop banded microstructures; the other class, based on Al–(Mg)–Mn, had near-equiaxed microstructures. In both classes, superplastic behaviour was found in the variants with the higher solute content. The evolution of the banded microstructures and the results from surface grid measurement in the Al–(Mg)–Mn alloys give results which indicate that the superplasticity is primarily a result of diffusion creep, and the effect of solute is proposed to be via an enhancement of solvent self-diffusion. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272815 Mon, 07 Dec 2009 00:00:00 +0100 3272815 http://www.medworm.com/index.php?rid=3272814&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008052%2Fabstract%3Frss%3Dyes Abstract: The performance of ferroelectric ceramics is governed by the ability of domains to switch. A decrease in the switching ability can lead to degradation of the materials and failure of ferroelectric devices. In this work the dynamic properties of domain reorientation are studied. In situ time-of-flight neutron diffraction is used to probe the evolution of ferroelastic domain texture under mechanical cyclic loading in bulk lead zirconate titanate ceramics. The high sensitivity of neutron diffraction to lattice strain is exploited to precisely analyze the change of domain texture and strain through a full-pattern Rietveld method. These results are then used to construct a viscoelastic model, which explainsthe correlation between macroscopic phenomena (i.e. creep and recovered deforma... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3272814 Mon, 07 Dec 2009 00:00:00 +0100 3272814 http://www.medworm.com/index.php?rid=3212142&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008040%2Fabstract%3Frss%3Dyes Abstract: The structural relaxation in a Zr55Cu30Ni5Al10 bulk metallic glass was investigated by volume and enthalpy relaxation at various temperatures. The relaxation kinetics was well described by a stretched exponential relaxation function, . The Kohlrausch index, β, ranged from 0.35 to 0.69, while the temperature dependence of relaxation time, τ was best fitted by the Vogel–Fulcher–Tanmmann formula, , with τ0=1.1×10−14 s, D∗=44.2 and T0=311K. Atomic volumes in the equilibrium liquid region were measured by the electrostatic levitation method and these volumes, together with volumes of relaxed glasses, were better described by the Cohen–Grest model than by the Cohen–Turnbull model. (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212142 Mon, 07 Dec 2009 00:00:00 +0100 3212142 http://www.medworm.com/index.php?rid=3212139&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008003%2Fabstract%3Frss%3Dyes Abstract: The evolution of an atomistic-level nanostructure during the early stages of secondary ageing of a rapid hardening Al–1.1Cu–1.7Mg (at.%) alloy has been characterized by a combination of atom probe tomography (APT) and transmission electron microscopy. Quantitative APT analysis reveals key changes in the evolution of solute clusters during secondary ageing (T6I4 condition) that correlate with secondary hardness increments. The microstructures that cause peak hardness differ between the T6 and T6I4 tempers – the former is a result of solute clustering as well as the precipitation of GPB zones and S phase, whereas in the latter, secondary ageing promotes only the formation of solute clusters. Cu–Mg clusters with high Mg:Cu ratio have the most strengthening potency during sec... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212139 Mon, 07 Dec 2009 00:00:00 +0100 3212139 http://www.medworm.com/index.php?rid=3212137&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409007988%2Fabstract%3Frss%3Dyes Abstract: A thermodynamic model has been presented for the prediction of the type of initial, amorphous oxide overgrowth (i.e. am-Al2O3, am-MgO or am-MgAl2O4) on bare AlMg substrates as a function of the Mg alloying element content at the substrate/oxide interface, the growth temperature and the oxide-film thickness (up to 5nm). On the basis of the macroscopic atom approach, expressions have been derived for the estimation of the energies of the interfaces between the AlMg substrate and the competing am-Al2O3, am-MgO and am-MgAl2O4 overgrowths. For all cases a strong driving force has been revealed for the interfacial (chemical) segregation of Mg. am-Al2O3 was found to be the most stable amorphous oxide phase on the AlMg substrate for T (Source: Acta Materialia) Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212137 Mon, 07 Dec 2009 00:00:00 +0100 3212137 http://www.medworm.com/index.php?rid=3212136&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409007976%2Fabstract%3Frss%3Dyes Abstract: In directional solidification, a sample is pulled in an externally imposed temperature gradient. When the pulling direction and the temperature gradient are not perfectly aligned, a transverse temperature gradient is generated in the sample. We investigate the dynamics of lamellar eutectic patterns, both by experimental observations and by numerical simulations, and find that it is dramatically affected by a transverse gradient. Whereas, in its absence, the labyrinth patterns that are formed in the initial stage of solidification persist over the entire duration of the experiments, a transverse temperature gradient induces a drift of the pattern which rapidly generates a regular array of lamellae. The drift speed is found to be consistently larger than expected from the normal gr... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212136 Mon, 07 Dec 2009 00:00:00 +0100 3212136 http://www.medworm.com/index.php?rid=3212135&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409007964%2Fabstract%3Frss%3Dyes We present phase-field simulations of isothermal phase transformations in the peritectic system below and above the peritectic temperature. The physical processes involved are of different natures, involving either a triple junction or a liquid-film-migration (LFM) mechanism. Below the peritectic temperature, one of the solid phases steadily grows along the other. Above the peritectic temperature the phase transformation proceeds via the LFM mechanism. To the best of our knowledge, this mechanism has not been discussed in the literature as a generic process of phase transitions in peritectic systems. In addition to the LFM process, we also simulate melting along the solid–solid interface. Finally, we make a simplified linear stability analysis of the liquid film, supporting our simulatio... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212135 Mon, 07 Dec 2009 00:00:00 +0100 3212135 http://www.medworm.com/index.php?rid=3212144&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008076%2Fabstract%3Frss%3Dyes Abstract: In situ and post-mortem diffraction contrast transmission electron microscopy (TEM) was used to study the multiplication of dislocations during a thermal martensitic forward and reverse transformation in a NiTi shape memory alloy single crystal. An analysis of the elongated dislocation loops which formed during the transformation was performed. It is proposed that the stress field of an approaching martensite needle activates an in-grown dislocation segment and generates characteristic narrow and elongated dislocation loops which expand on {110}B2 planes parallel to {001}B19′ compound twin planes. The findings are compared with TEM results reported in the literature for NiTi and other shape memory alloys. It is suggested that the type of dislocation multiplication mechanism doc... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212144 Fri, 04 Dec 2009 00:00:00 +0100 3212144 http://www.medworm.com/index.php?rid=3212141&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409008039%2Fabstract%3Frss%3Dyes Abstract: The mechanical behaviour of nanoporous superalloy membranes is analysed for the first time and discussed in conjunction with their microstructure, consisting of ligaments of the γ′ phase and channel-like pores a few hundred nanometers wide. Tensile tests and vibrating reed experiments are performed to determine the mechanical properties. It is shown that they are strongly dependent on the processing procedure, the orientation of the γ′ ligaments and interdendritic heterogeneities. A microstructural model of the membrane materials is then used to analyse the findings in more detail and rationalize the observed elastic behaviour. Following these results, unique metallic membrane materials can be produced, combining excellent strength on a macroscopic scale with extremely fine... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212141 Fri, 04 Dec 2009 00:00:00 +0100 3212141 http://www.medworm.com/index.php?rid=3212134&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409007952%2Fabstract%3Frss%3Dyes Abstract: Interest in Fe(ND3)2PO4, one of the first three-dimensional structurally linked solids forming Fe–ND3 bonds, has been renewed recently due to the observation of structural and magnetic phase transitions. This paper reports powder neutron diffraction experiments which show that Fe(ND3)2PO4 crystallizes at room temperature in an orthorhombic (Pnma) crystal structure, but that below Tt=226(5)K the crystal progressively adopts a monoclinic (P21/n) structure via a continuous phase transition, as observed from heat capacity measurements in the temperature range 250–100K. In addition, neutron diffraction experiments suggest that the magnetic structure is non-collinear with an incommensurate propagation vector , with τ ∼0.04 reciprocal lattice units (rlus), and that the magnitude ... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212134 Fri, 04 Dec 2009 00:00:00 +0100 3212134 http://www.medworm.com/index.php?rid=3212111&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409007587%2Fabstract%3Frss%3Dyes Abstract: A water-based precursor solution was used to deposit a thin layer (70nm) on a NiW substrate. The characterization of the (LZO) consisted of X-ray diffraction, pole figures, reflection high-energy electron diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy (TEM) of the cross-section. The results reveal that high-quality LZO layers can be produced using completely water-based solutions, rendering a high degree of texture (full width at half maximum=6.5°). In order to test the quality of this coating as a buffer layer, a 350nm thick layer of YBCO was deposited by metal organic chemical vapor deposition. The superconducting properties were measured inductively (Cryoscan, THEVA). A thorough TEM study of all the interfaces present w... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212111 Thu, 03 Dec 2009 00:00:00 +0100 3212111 http://www.medworm.com/index.php?rid=3212138&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS135964540900799X%2Fabstract%3Frss%3Dyes Abstract: A new model is proposed that aims to capture within a single modelling frame all the main microstructural features of a severe plastic deformation process. These are: evolution of the grain size distribution, misorientation distribution, crystallographic texture and the strain-hardening of the material. The model is based on the lattice curvature that develops in all deformed grains. The basic assumption is that lattice rotation within an individual grain is impeded near the grain boundaries by the constraining effects of the neighbouring grains, which gives rise to lattice curvature. On that basis, a fragmentation scheme is developed which is integrated in the Taylor viscoplastic polycrystal model. Dislocation density evolution is traced for each grain, which includes the contri... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212138 Mon, 30 Nov 2009 00:00:00 +0100 3212138 http://www.medworm.com/index.php?rid=3212133&cid=s_38391_173_f&fid=38391&url=http%3A%2F%2Fwww.actamat.org%2Farticle%2FPIIS1359645409007940%2Fabstract%3Frss%3Dyes Abstract: The presence of aluminum nitride in nanostructured aluminum metal matrix composites was studied by high resolution transmission electron microscopy, electron energy loss spectroscopy, energy dispersive X-ray spectroscopy analysis and electron microscopy simulations. Three types of aluminum nitride structures were identified; predominantly, one layer of N atoms occupies the tetrahedral interstitial positions in the Al lattice, the frequency of which varies as a function of spatial location. The second and third were in the form of hexagonal and possibly cubic aluminum nitride particles with particle sizes on the order of 15–20nm. The results suggest that the aluminum nitride phase evolves from intermediate transitional structures that involve N atoms in the Al lattice. The alumi... Acta Materialia journals http://www.medworm.com/rss/comments.php?id=3212133 Mon, 30 Nov 2009 00:00:00 +0100 3212133