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This study investigated the influence of parent austenite grain refinement on the intervariant boundary network (population and connectivity) in a lath martensitic steel. Parent austenite grain refinement revealed a progressive reduction in the fraction of the 60° misorientation boundaries in martensite, which was linked to a decrease in the 60 ° / [ 110 ] intervariant boundary population. The phenomenological theory of martensite crystallography demonstrated that the variant selection mechanism altered from the 3-variant clustering (V 1 V 3 V 5) in the coarse parent austenite towards the 4-variant clustering (V 1 V 2 V 3 V 4) in the fine parent austenite grain, due to the change in the lattice parameter of the parent and daughter phase in which the martensite transformation occurs, as measured using in situ neutron diffraction. The change in the variant clustering arrangement with the parent austenite grain refinement led to a progressive promotion of 60 ° / [ 111 ] and 10.5 ° / [ 011 ] intervariant boundaries at the expense of 60 ° / [ 110 ] martensite intervariant boundaries. Subsequently, the connectivity of low energy {110} tilt intervariant boundaries gradually increased through the refinement of parent austenite grain size, eventually reducing the high energy {110} twist boundary connectivity. This change improved the impact toughness of martensite produced from the fine-grained austenite as the weak connectivity of high energy boundaries delays the coalescence of voids, promoting ductile fracture. [ABSTRACT FROM AUTHOR]

The use of Ti6Al4V alloy in critical aerospace applications among other titanium alloys is higher due to the high strength, toughness and corrosion resistance characteristics. Achieved combination of strength and toughness is directly related to the bimodal (equiaxed alpha plus transformed beta) microstructure obtained by hot working of this alloy in a narrow strain rate and temperature domain. Present study distinctly describes the evolution of microstructure during hot deformation as an effect of process conditions and initial microstructure characteristics of Ti6Al4V alloy. The initial microstructure and processing conditions significantly influenced the evolution of β phase and dynamic recrystallization behaviour. An increase in β phase fraction was observed due to the increased adiabatic temperature at higher strain rates during α+β working. The increase in volume fraction of stable β phase as result of vanadium diffusion during hot working revealed the existence of strain induced phase transformation. Continuous dynamic recrystallization (CDRX) led to the fragmentation of initial α grains, and the effect of initial grain orientation on the CDRX mechanism was studied. The initial grains with the basal plane parallel to the compression direction revealed large fragmentation due to the high resistance to deformation. A CDRX mechanism map was developed based on the effect of processing conditions and initial grain characteristics. • Strain induced phase transformation by the depletion of V from supersaturated α. • Effect of initial grain orientation characteristics with process parameters. • Dominant Continuous Dynamic Recrystallization mechanism of Ti6Al4V alloy. • Recrystallization mechanism map considering process conditions and microstructure. [ABSTRACT FROM AUTHOR]

The intervariant boundary characteristics of a commercially pure Ti microstructure formed by the β → α martensitic phase transformation were described according to the crystallography of the displacive transformation and the boundary plane orientation. The martensitic transformation created a microstructure whose grain boundary misorientation angle distribution had four distinct peaks that were consistent with the misorientations between the variants produced by the Burgers orientation relationship. Interestingly, about 60% of population corresponded to 60°/ [ 11 2 ¯ 0 ] intervariant boundaries. Three-variant clusters with a triangular morphology were observed frequently. This configuration is consistent with the phenomenological theory of martensite, which predicts that these clusters, separated by 60°/ [ 11 2 ¯ 0 ] boundaries, have a lower transformation strain than other possible variant cluster arrangements. Other intervariant boundaries resulted from the impingement of different combinations of distinct three-variant clusters. The five-parameter boundary analysis revealed a strong anisotropy in the plane orientation distribution, showing that boundaries have a tendency to terminate on prismatic { h k i 0 } and pyramidal { 10 1 ¯ 1 } planes, when misorientation was ignored. The dominant 60°/ [ 11 2 ¯ 0 ] intervariant boundaries had symmetric tilt ( 1 ¯ 101 ) boundary planes, which are a low energy configuration. [ABSTRACT FROM AUTHOR]

Compression Test (CT) plays a fundamental role in our understanding of materials science and engineering. This is due to the test's capacity to physically simulate different deformation scenarios. Mechanics of CT is critical to model stored energy, microstructure and behaviours in a deforming material. To simulate “shear and heterogeneous” deformation, friction, constitutive behaviour, etc., new closed form solutions of CT are needed. Developing detailed solutions for the test is a fundamental priority to represent the deformation more reliably. Expressions for effective strain and the test sample's free surface were derived here to extend “Avitzur's solution” beyond a limit analysis. The extended Avitzur (EA) solution was employed in a “constant friction factor mode” to make it more comparable with other reference solutions such as the Cylindrical Profile Model (CPM) and the Finite Element (FE). Example EA and CPM solutions were obtained and compared to those of a FE model. Partial enforcement of incompressibility and a rough estimation of barrelling parameter in Avitzur solution were found to be responsible for unrealistic prediction of the sample's profile and friction factor. EA's effective strain and strain rate along the sample's centre line, particularly at its centre, agreed well with the FE predictions. Therefore, the sample centre was suggested as the representative point at which the deformation path can be traced for the constitutive modelling using EA solution. [ABSTRACT FROM AUTHOR]

Hot-deformation can refine grain size and change the dynamics of austenite-ferrite phase transformation during thermo-mechanical processing of microalloyed steels. Here, atom probe tomography has been used to characterize nanoscale precipitates and segregation in Ti-Mo microalloyed steels processed with and without hot-deformation at 890 °C. It provides a comprehensive understanding of solute redistribution in both the grain interior and grain boundary regions. The results show that coarse (Ti, Mo)C precipitates are formed at grain boundaries, whereas fine precipitates are densely distributed in grain interiors, regardless of deformation conditions. Precipitate-free zones are developed near grain boundaries in the undeformed Ti-Mo steel, but absent in the hot-deformed steel. The elimination of precipitate-free zone in the hot-deformed steel is attributed to the high dislocation density and accelerated γ → α transformation caused by hot-deformation. The majority of Ti, Mo, and C atoms partition into (Ti, Mo)C precipitates, but Mn, Si, and Al atoms are mainly in solute state in ferrite matrix and segregation at grain boundaries. The hot-deformation significantly changes the C segregation at grain boundaries, but has little effect on other solute elements. [ABSTRACT FROM AUTHOR]

In the current study, a Ti-6Al-4V alloy plate with a supersaturated martensitic starting microstructure was initially warm rolled, producing a gradient ultrafine-grained (UFG) microstructure throughout the thickness: fully equiaxed UFG in the surface layer and a combination of UFG and elongated grains in the center layer. The thermal stability of the warm rolled UFG microstructures was then investigated through the course of post-deformation annealing treatment. Upon annealing, the fully UFG surface layer experienced concurrent α grain growth and β precipitation (i.e. partitioning), whereas the center layer revealed the replacement of partially fragmented α lath by equiaxed grains, most likely through static recrystallization. With increasing annealing time, the overall texture characteristics were mostly preserved for both surface and center layers, apart from a gradual strengthening of the (0°, 0°, 30°) texture component in the surface layer at the expense of the (0°, 0°, 0°) and (0°, 90°, 0°) components. The current post-deformation annealing treatment led to an enhanced tensile elongation of the alloy at the expense of strength, with an increase in the annealing time. [ABSTRACT FROM AUTHOR]

The structure, energy and bonding property of TixCy clusters formed in iron matrix were studied through molecular dynamics (MD) simulation method. The initial clusters with 1D-linear, 2D-ring, and 3D-tetrahedral structures were determined and their stability was calculated. The effect of temperature on the stability of the clusters was also discussed. In addition, the dissociation path of TiC clusters in iron matrix and the corresponding energy variation were analyzed. [ABSTRACT FROM AUTHOR]

The microstructural response and deformation mechanisms under cyclic and monotonic loading were investigated in a commercially pure Al subjected to grain refinement by cryorolling. A fatigue dependent shear banding and grain coarsening was detected and it was shown that pre-existing shear bands induced by cryorolling play a vital role in this regard. A rapid initial cyclic softening dominated by activation of pre-existing shear bands is replaced by a more gradual cyclic softening dominated by grain coarsening within these shear bands. [Copyright &y& Elsevier]

To study the effect of deformation mode used for grain refinement on the low-cycle-fatigue (LCF) behaviour of ultrafine-grained (UFG) materials, a commercially pure Al was subjected to cryorolling, and room temperature symmetric and asymmetric rolling. The LCF test was conducted under fully reversed total strain amplitude control. Despite its lower tensile ductility, the cryorolled Al had significantly higher fatigue ductility. This has been attributed to a higher density of shear bands in the cryorolled Al. [Copyright &y& Elsevier]

Abstract: Commercially pure aluminium and 2024 Al alloy were cryo-rolled and annealed to produce ultrafine grained (UFG) microstructures. Both materials were cyclically deformed under a fully reversed total strain amplitude control condition at different frequencies to study strain rate effects. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify microstructural changes and explain the mechanical properties. The cyclic stress response showed significant softening in commercial purity Al that was due to shear band formation and grain coarsening within these shear bands. While there was no strain rate sensitivity for commercial purity Al in terms of the mechanical response, the shear bands became noticeably more defined at lower strain rates. 2024 Al alloy had a cyclically stable response and microstructure that was not affected by strain rate. [Copyright &y& Elsevier]

Abstract: The cyclic deformation response of ultrafine pure Al produced by cryo-rolling was investigated using low-cycle fatigue and electron microscopy. The ultrafine pure Al was cyclically deformed under a fully reversed total strain control (R =−1) corresponding to a plastic strain amplitude range of 8×10−4 and 1.4×10−2. It was found that cryo-rolled pure Al is very susceptible to cyclic softening, resulting in a much lower fatigue life compared with the coarse-grained counterpart. Shear banding and associated grain coarsening were the most prominent microstructural features of the cyclically deformed cryo-rolled pure Al. Furthermore, annealing led to a slight decrease in the cyclic softening rate, giving a slight increase in the fatigue life of cryo-rolled Al. [Copyright &y& Elsevier]

Abstract: The structural characteristics of biomedical porous materials are crucial for bone tissue to grow into a porous structure and can also influence the fixation and remodeling between the implant and the human tissues. The current study has been investigating the effect of the ball-milling variable of time on the structural characteristics and pore morphology of a biomedical porous Ti–16Sn–4Nb (wt.%) alloy. The alloy was synthesized using high-energy ball milling for different periods of time, and the porous Ti–16Sn–4Nb alloy was fabricated by using a space holder sintering process. The resultant powder particles, bulk, and porous samples were characterized using a scanning electron microscope (SEM), laser particle-size analyzer, chemical analysis, X-ray diffraction analysis (XRD), and the Vickers hardness test. The results indicated that the inner pore surface, pore wall architecture, degree of porosity, pore size and the inter-pore connectivity of the sintered porous alloy are all considerably affected by ball-milling time. [Copyright &y& Elsevier]

Abstract: Cryo-rolled 2024 aluminium alloy was investigated using low cycle fatigue and electron microscopy. The cryo-rolled 2024 Al alloy was cyclically deformed under a fully reversed total strain control (R =−1) in the plastic strain amplitude range of 8×10−4 to 1×10−2. This study revealed the beneficial effect of the presence of precipitates in the microstructure on the cyclic stability. In addition, there was no evidence of microstructural instabilities, such as grain coarsening or bulk shear banding. Moreover, artificial aging of cryo-rolled 2024 Al alloy was found ineffective in terms of improving fatigue life. [ABSTRACT FROM AUTHOR]

In this study, the effects of calcium (Ca) and yttrium (Y) on the microstructure, mechanical properties, corrosion behaviour and biocompatibility of magnesium (Mg) alloys, i.e. Mg- xCa ( x = 0.5, 1.0, 2.0, 5.0, 10.0, 15.0 and 20.0%, wt%, hereafter) and Mg-1Ca-1Y, were investigated. Optical microscopy, X-ray diffractometry (XRD), compressive and Vickers hardness testing were used for the characterisation and evaluation of the microstructure and mechanical properties. The in vitro cytotoxicity of the alloys was assessed using osteoblast-like SaOS2 cells. The corrosion behaviour of these alloys was evaluated by soaking the alloys in simulated body fluid (SBF) and modified minimum essential medium (MMEM) at 37 °C in a humidified atmosphere with 5% CO. Results indicated that the increase of the Ca content enhances the compressive strength, elastic modulus and hardness of the Mg-Ca alloys, but deteriorates the ductility, corrosion resistance and biocompatibility of the Mg-Ca alloys. The Y addition leads to an increase in the ductility; but a decrease in the compressive strength, hardness, corrosion resistance and biocompatibility of the Mg-1Ca-1Y alloy when compared to the Mg-1Ca alloy. Solutions of SBF and MMEM with the immersion of Mg- xCa and Mg-1Ca-1Y alloys show strong alkalisation. Our research results indicate that Mg- xCa alloys with Ca additions less than 1.0 wt% exhibited good biocompatibility, low corrosion rate as well as appropriate elastic modulus and strength; whilst the Y is not a proper element for Mg alloys for biomedical application due to its negative effects to the corrosion resistance and biocompatibility. [ABSTRACT FROM AUTHOR]

Abstract: The effects of nanoscale pores on the strength and ductility of porous Cu46Zr54 metallic glasses during nanoindentation and uniaxial compression tests are modelled and investigated using molecular dynamics (MD) simulations. In the MD simulations, atomistic amorphous samples were digitally prepared through fast quenching from the liquid states of copper and zirconium alloy. In both of the nanoindentation and uniaxial compression simulations, shear transformation zones and shear bands are observed through the local deviatoric shear strains in the samples. The results show that the existence of pores causes strain concentrations and greatly promotes the initialization and propagation of shear bands. Importantly, only pores reaching critical size can effectively facilitate the formation of multiple shear bands. It is also observed that hardening occurs through pore annihilation and the shear band stops in porous metallic glasses. [ABSTRACT FROM AUTHOR]

Despite the high demand for industrial applications of magnesium, the forming technology for wrought magnesium alloys is not fully developed due to the limited ductility and high sensitivity to the processing parameters. The processing window for magnesium alloys could be significantly widened if the lower-bound ductility (LBD) for a range of stresses, temperature, and strain rates was known. LBD is the critical strain at the moment of fracture as a function of stress state and temperature. Measurements of LBD are normally performed by testing in a hyperbaric chamnber which is highly specialized, complex, and rare equipment. In this paper an alternative approach to determine LBD is demonstrated using wrought magnesium alloy AZ31 as an example. A series of compression tests of bulge specimens combined with finite element simulation of the tests were performed. The LBD diagram was then deduced by backward calculation. [ABSTRACT FROM AUTHOR]

The influence of the parent austenite deformation state on the intervariant boundary network (i.e., population, plane orientation, and connectivity) of a lath martensitic microstructure was investigated using conventional EBSD mapping and five-parameter boundary analysis approach along with quantification of boundary connectivity using homology metrics. The lath martensite largely revealed a bimodal misorientation angle distribution, closely matched with the Kurdjumov–Sachs (K–S) orientation relationship. The application of deformation significantly changed the distribution, gradually reducing the intensity of the 60° misorientation angle peak. This was largely ascribed to substructure development within the parent austenite upon deformation, which stimulates particular variant/s having a habit plane (011)α′ closely parallel to the primary (111)γ and/or secondary (1 1 ¯ 1)γ slip plane. The interaction of these variants eventually promoted specific intervariant boundaries (e.g., 60°/[111], 10.5°/[011], and 49.5°/[110]) at the expense of 60°/[011]. The application of deformation in the parent austenite did not change the intervariant boundary plane character distribution, which mostly exhibited an anisotropic character terminated on {110} planes because of the displacive nature of the martensitic transformation. However, the extent of anisotropy progressively decreased with increasing strain in the austenite prior to transformation. The grain boundary network connectivity was markedly altered due to the local variant selection induced by the deformation. Deformation in the austenite regime generally decreased the connectivity of boundaries having a {110} plane orientation. The intervariant boundaries with the {110} twist character also displayed a similar trend, though the connectivity of {110} tilt boundaries progressively enhanced with increasing strain. The former was closely matched with a decrease in the population of 60°/[110] intervariant boundaries with the strain. The current findings suggest that the intervariant boundary network of lath martensite can be manipulated through changes in the parent austenite deformation state which, in turn, can be used to enhance key final product properties such as toughness. [ABSTRACT FROM AUTHOR]

Solid-state additive friction stir deposition was employed to three dimensionally print a 316L stainless steel. The microstructure, texture and grain boundary distribution were characterised using five-parameter boundary analysis. The bulk microstructure was exceptionally fine (∼0.7 µm) throughout the thickness of the deposited layers, consisting of equiaxed grains along with sub-grains delineated by high and low angle boundary segments. The misorientation angle distribution of the deposited layers was considerably different from the as-received microstructure, exhibiting a significant reduction in the relative areas of ∑3 annealing twin boundaries due to their distortion by severe plastic deformation. The overall texture also exhibited strong shear components associated with FCC metals, suggesting that the microstructure refinement largely took place through progressive subgrain rotation, known as continuous dynamic recrystallisation. The grain boundary plane distribution revealed significantly lower anisotropy compared with the as-received material, showing two moderate peaks at the (111) and (110) orientations. The migration of high-angle mobile boundaries, which may have been induced by thermal cycle upon subsequent deposition along with the dislocation gradients between adjacent grains, slightly enhanced the intensity of low energy (111) orientations at the expense of (110) high-energy boundaries. [ABSTRACT FROM AUTHOR]

The characteristics of the intervariant boundary network that resulted from the β → α ′ martensitic phase transformation in a Ti–6Al–4V alloy were studied using the crystallographic theories of displacive transformations, five-parameter grain boundary analysis and triple junction analysis. The microstructure of Ti–6Al–4V martensite consisted of fine laths containing dislocations and fine twins. The misorientation angle distribution revealed four distinct peaks consistent with the intervariant boundaries expected from the Burgers orientation relationship. The phenomenological theory of martensite predicted four-variant clustering to have the lowest transformation strain among different variant clustering combinations. This configuration was consistent with the observed Ti–6Al–4V martensitic microstructure, where four-variant clusters consisted of two pairs of distinct V-shape variants. The 63. 26 ∘ / [ 10 ¯ 5 5 3 ¯ ] α ′ and 60 ∘ / [ 1 1 2 ¯ 0 ] α ′ intervariant boundaries accounted for ~ 38% and 33% of the total population, respectively. The five-parameter boundary analysis showed that the former had a twist character, being terminated on the (3 ¯ 2 1 0) α ′ plane, and the latter revealed a symmetric tilt (1 0 1 ¯ 1) α ′ boundary plane. The 63. 26 ∘ / [ 10 ¯ 5 5 3 ¯ ] α ′ and 60 ∘ / [ 1 1 2 ¯ 0 ] α ′ had the highest connectivity at triple junctions among other intervariant boundaries. Interestingly, the boundary network in Ti–6Al–4V martensite was significantly different from the commercially pure Ti martensite, where only 60 ∘ / [ 1 1 2 ¯ 0 ] α ′ intervariant boundaries largely were found at triple junctions due to the formation of three-variant clustering to minimize the transformation strain. This difference is thought to result from a change in the martensitic transformation mechanism (slip vs twinning) caused by the alloy composition. [ABSTRACT FROM AUTHOR]

A series of Mg-Y-Ni alloys with different volume fractions of long-period stacking-ordered (LPSO) phase were prepared, by controlling the alloy composition, heat treatment, and single-pass extrusion, to assess the influence of increasing LPSO phase volume fraction on the hydrogen absorption and desorption properties of the extruded alloys. The LPSO phase volume fraction in the alloys increased with increasing solute concentration, from ~24% LPSO in Mg97Y2Ni1 (at.%) to ~60% LPSO in Mg93Y4Ni3 (at.%) up to ~92% LPSO in Mg91Y5Ni4 (at.%). The most refined microstructure was obtained in the alloy with highest volume fraction of LPSO phase. After 100 s at 300 °C, the Mg91Y5Ni4 alloy absorbed 4.6 ± 0.2 wt.% H while the Mg97Y2Ni1 and Mg93Y4Ni3 alloys each absorbed 3.8 ± 0.2 wt.% H. After 10,000 s at 300 °C, all three alloys had absorbed a maximum of 5.3 ± 0.2 wt.% H with no further significant difference in hydrogen absorption kinetics. The Mg91Y5Ni4 alloy desorbed 1.8 ± 0.2 wt.% H after 100 s at 300 °C against a vacuum while the Mg97Y2Ni1 and Mg93Y4Ni3 alloys desorbed 0.8 ± 0.2 wt. H and 0.6 ± 0.2 wt.% H, respectively. After 10,000 s at 300 °C, the Mg91Y5Ni4 and Mg97Y2Ni1 alloys completely desorbed 5.2 ± 0.2 wt.% H and 5.4 ± 0.2 wt.% H, respectively, but the Mg93Y4Ni3 alloy desorbed only 3.7 ± 0.2 wt.% H. Hydrogen absorption and desorption kinetics were fastest in the Mg91Y5Ni4 alloy with the highest LPSO volume fraction, but no consistent trend with LPSO phase volume fraction was observed with the Mg93Y4Ni3 alloy, which showed the slowest absorption and desorption kinetics. The hydrogen pressures corresponding to metal–hydride equilibrium did not vary with LPSO phase volume fraction or alloy composition, indicating that the (de)hydrogenation thermodynamics were not significantly changed in any of the alloys. Hydrogen absorption experiments with thin foils, made of extruded Mg91Y5Ni4 alloy with the highest LPSO phase fraction, demonstrated that the LPSO structures decompose into Mg phase, Mg2Ni phase, lamellar Mg/Mg-Y structures, and YHx particles. This study shows that hydrogen kinetics can be impacted in Mg-Y-Ni alloys by controlling the LPSO phases using common metallurgical techniques. [ABSTRACT FROM AUTHOR]

A series of Mg–Y–Zn alloys with varying long-period stacking ordered (LPSO) phase fractions were prepared through control of alloy content, heat-treatment, and single-pass extrusion. The effect of LPSO phase volume fraction and microstructure refinement on the hydrogen absorption/desorption properties of ball-milled powders prepared from the extruded alloys was experimentally assessed. The hydrogen absorption and desorption kinetics scaled with the LPSO phase volume fraction, though the results of this study suggest that the scaling is not linear. Variations in the LPSO phase fraction and alloy content did not alter the (de)hydrogenation equilibrium pressure, indicating there is no significant change in thermodynamics of hydrogenation. Hydrogen absorption experiments on thin foils made from the extruded Mg–Y–Zn alloy with a high LPSO phase fraction demonstrated that the LPSO structures decompose into Mg phase, lamellar Mg/Mg–Zn structures and YH2 particles at hydrogen partial pressures sufficient to form YH2. This study shows that the hydrogen absorption/desorption kinetics in the Mg–Y–Zn alloys can be controlled by tailoring the LPSO phases using conventional metallurgical techniques. [ABSTRACT FROM AUTHOR]

Plastic strain gradients can influence the work-hardening behaviour of metals due to the accumulation of geometrically necessary discolations at the micron/submicron scale. A finite element model based on the conventional theory of mechanism-based strain-gradient plasticity has been developed to simulate the micropillar compression of Cu–Fe thin films and multilayers. The modelling results show that the geometric constraints lead to inhomogeneous deformation in the Cu layers, which agrees well with the bulging of Cu layers observed experimentally. Plastic strain gradients develop inside the individual layers, leading to extra work-hardening due to the accumulation of geometrically necessary dislocations. In the multilayer specimens, the Cu layers deform more severely than the Fe layers, resulting in the development of tensile stresses in the Fe layers. It is proposed that these tensile stresses are responsible for the development of micro-cracks in the Fe layers. [ABSTRACT FROM AUTHOR]

Nano-textured porous metal materials present unique surface properties due to their enhanced surface energy with potential applications in sensing, molecular separation and catalysis. In this paper, commercial alloy foils, including brass (Cu85Zn15 and Cu70Zn30) and white gold (Au50Ag50) foils have been chemically de-alloyed to form nano-porous thin films. The impact of the initial alloy micro-structure and number of phases, as well as chemical de-alloying (DA) parameters, including etchant concentration, time and solution temperature on the final nano-porous thin film morphology and properties were investigated by electron microscopy (EM). Furthermore, the penetration depth of the pores across the alloys were evaluated through the preparation of cross sections by focus ion beam(FIB)milling. It is demonstrated that ordered pores ranging between 100 nm and 600 nm in diameter and 2'5 'm in depth can be successfully formed for the range of materials tested. The microstructure of the foils were obtained by electron back-scattered diffraction (EBSD) and linked to development of pits across the material thickness and surface during DA. The role of selective etching of both noble and sacrificial metal phases of the alloy were discussed in light of the competitive surface etching across the range of microstructures and materials tested. [ABSTRACT FROM AUTHOR]

Tempering has been used as a method to develop a range of dual phase steels with the same martensite morphology and volume fraction, but containing phases with different relative strengths. These steels were used to examine the strain partitioning between the two constituent phases experimentally through mechanical testing and numerically through finite element modelling. It was found that increasing the differential in strength between the two phases not only produces regions of high strain, but also regions of low strain. On average, a larger difference in strength between the phases increased the strain carried by the softer phase. There was no discernible preferential strain localisation to the ferrite/martensite interface, with the regions of strain localisation being determined by the morphology of the microstructure. A direct correlation between the average strain in the ferrite, and the measured ductility has been found. [ABSTRACT FROM AUTHOR]

Microcompression tests of Cu/Fe multilayers with diameters ranging from 0.6 to 2.0μm show that the flow stress increases with increasing pillar diameter, which implies that “larger is stronger”. Finite element analysis results explain the stress and strain distributions in the pillars, and suggest that the dimensional constraint is responsible for the strengthening. This work reveals a new mechanism of extrinsic size effect in polycrystalline multilayer pillars, which is opposite to the extrinsic size effect in single-crystal pillars. [ABSTRACT FROM AUTHOR]

The strain partitioning of ferrite and martensite in a dual-phase steel after tensile deformation has been investigated. There was more strain accommodated in the ferrite phase due to its being the softer of the two phases. The orientation of the ferrite was not found to contribute to strain localization, and it was concluded that the morphology of the microstructure was the most dominant factor affecting strain localization. [ABSTRACT FROM AUTHOR]

Abstract: It is important to understand the cellular and molecular events that take place at the cell–material interface of implants used for bone repair. An understanding of the mechanisms involved in the initial stages of osteoblast interactions with the surface of the implant material is fundamental in deciding the fate of the cells that come in contact with it. In this study, we compared the relative gene expression of markers that are known to be associated with cell adhesion and differentiation in MC3T3 osteoblast cells, at various time points after plating the cells on surfaces of titanium (Ti) and its two alloys, titanium–zirconium (TiZr) and titanium–niobium (TiNb) by using Quantitative Real Time Polymerase Chain Reaction (RT-PCR). Our analysis indicated that expression of adhesion supporting genes was higher on TiZr surface as compared to Ti and TiNb. The behavior of these genes is possibly driven by a higher surface energy of TiZr. However no significant difference in the expression of differentiation related genes could be seen between the two alloys, although on both substrates it was higher as compared to unalloyed Ti. We propose that substrate composition of the alloys can influence the adhesion and differentiation related gene expression and that Ti alloys are better substrates for inducing osteogenesis as compared to unalloyed Ti. [Copyright &y& Elsevier]

We report the successful molecular-beam epitaxial growthof 10stacked layers of GaSb/GaAs quantum rings using a new procedure. Exactcontrol of the arsenic flux during capping helps to reduce the stronggroup-V As–Sb exchange reactions, enabling the rings to becapped at the same growth temperature (480 °C) without dissolution.X-ray diffraction and transmission electron microscopy indicate excellentstructural quality and uniformity with no threading dislocations.This is due to the reduction in the average strain through the quantum-ringformation. The total ring density in the stacks is 1 × 1011cm–2. An unusually long-wavelength quantum-ringphotoluminescence peak of 1.3 μm is observed at low temperature,which is attributed to a reduction in the quantum-ring charging dueto lower unintentional p-doping in the GaAs cap layer. The impactthat this effect will have on future device designs in solar cellsand lasers is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Skin passing or temper rolling introduces a strain gradient through the thickness of the sheet which, in turn, results in a residual stress profile through the thickness. These residual stresses can have a major effect on the elastic–plastic transition in bending operations, but the effect of residual stresses on downstream forming has yet to be determined. In this work, a commercial aluminium alloy, AA6063, was reduced in thickness by rolling in a laboratory mill to introduce residual stresses into the material. The strips were then tested in tension and pure bending and the material behaviour close to the elastic–plastic transition investigated. Substantial lowering of the elastic–plastic transition in the bending moment was observed while the opposite trend was found in the tensile test. The rolling process was analyzed using finite element analysis and the distribution of residual stresses determined; theoretical moment curvature characteristics were obtained using the output of this analysis as the input to the modelling for pure bending. The results show qualitatively how the material is softened in bending after rolling and demonstrate that this is partly due to the residual stress gradients in the material. [Copyright &y& Elsevier]

Abstract: The mechanical behaviours of metal foams greatly depend on their cell topology, including cell shape, cell size etc. as well as relative density and material properties of the cell wall. However, the cell shape effect on the mechanical behaviours of such materials appears to be ignored in previous research. In this paper, both analytic and finite element models are developed and employed to investigate the effect of cell shape on the mechanical behaviour of open-cell magnesium alloy (AZ91) foams under compression, including deformation modes and failure modes. For numerical modelling, both two-dimensional (2-D) and three-dimensional (3-D) finite element models are developed to predict the compressive behaviours of typical open-cell metal foams and capture the deformation modes and failure mechanisms. Two typical cell shapes i.e. cubic and diamond are taken into consideration. To validate these models, the analytic and numerical results are compared to the experimental data. Both the numerical and experimental data indicate that the cell shape significantly affects the compression behaviour of open-cell metal foams. In general, numerical results from the three-dimensional solid-element model show better agreement with the experimental results than those from other finite element models. [Copyright &y& Elsevier]

Abstract: In this study, titanium (Ti) and titanium–zirconium (TiZr) alloy samples fabricated through powder metallurgy were surface modified by alkali-heat treatment and calcium (Ca)-ion-deposition. The alteration of the surface morphology and the chemistry of the Ti and TiZr after surface modification were examined. The bioactivity of the Ti and TiZr alloys after the surface modification was demonstrated. Subsequently, the cytocompatibility of the surface modified Ti and TiZr was evaluated via in vitro cell culture using human osteoblast-like cells (SaOS2). The cellular attachment, adhesion and proliferation after cell culture for 14days were characterized by scanning electron microscopy (SEM) and MTT assay. The relationship between surface morphology and chemical composition of the surface modified Ti and TiZr and cellular responses was investigated. Results indicated that the surface-modified Ti and TiZr alloys exhibited excellent in vitro cytocompatibility together with satisfactory bioactivity. Since osteoblast adhesion and proliferation are essential prerequisites for a successful implant in vivo, these results provide evidence that Ti and TiZr alloys after appropriate surface modification are promising biomaterials for hard tissue replacement. [Copyright &y& Elsevier]

Abstract: In the current study, the relation between the softening behaviour and the grain structure, dislocation substructure and crystallographic texture development was investigated during post-deformation annealing of a fully dynamically recrystallized (DRX) austenitic Ni–30%Fe model alloy. The present observations revealed a novel mechanism of post-dynamic softening consisting of several concurrent processes. The initial softening stage involves rapid growth of the dynamically formed nuclei and migration of the mobile boundaries. Simultaneously, the sub-boundaries within DRX grains progressively disintegrate through dislocation climb and dislocation annihilation. This eventually leads to the formation of dislocation-free grains, and reduction in the rate of grain boundary migration. As a result, the DRX texture largely remains preserved throughout the annealing process. Furthermore, the visibility of extrinsic grain/twin boundary dislocations, originated from absorbed glide lattice dislocations during the DRX process, gradually decreases during the post-deformation annealing, as a result of their mutual annihilation and progressive incorporation into the boundary structure. [ABSTRACT FROM AUTHOR]

Abstract: Substructure development in an austenitic Ni–30%Fe model alloy was investigated within a dynamic recrystallization (DRX) regime. The substructure characteristics of the deformed matrix and DRX grains were markedly different regardless of the grain size and orientation. The former largely displayed ‘organized’, banded subgrain arrangements with alternating misorientations, resulting from a limited number of active slip systems. In contrast, the substructure of DRX grains was generally more ‘random’ and exhibited complex subgrain/cell arrangements characterized by local accumulation of misorientations, suggesting multiple slip. The proposed mechanism of the unique substructure development within DRX grains suggests that the DRX nuclei, forming along pre-existing grain boundaries and triple points, essentially represent grain boundary regions, which experience multiple slip to preserve the compatibility with neighbouring deformed grains. This results in the formation of a complex cell/subgrain structure, which progressively extends as the grain boundary regions expand outwards during DRX growth. [Copyright &y& Elsevier]

Abstract: The physical properties of the new porous Ti6Ta4Sn alloy scaffold, including the porosity and the pore size and various surface modifications, were investigated in terms of its effect on osteoblast-like SaOS2 cells. Results indicated that the cell adhesion density on the scaffolds was directly proportional to porosity in the range of 25–75%, but was inversely proportional to pore size in the range of 75–900μm. Surface modifications, including alkali-heat treatment (AH), sol–gel hydroxyapatite coating (HA) and alkali-heat treatment plus simulated body fluid (SBF) soaking, significantly enhanced the osteoblast-like cell adhesion on the Ti6Ta4Sn scaffold. It is also noticed that the sol–gel hydroxyapatite coating process was more effective compared to the other two processes (AH and AH plus SBF soaking) in terms of enhancing the cell adhesion density of the scaffold. The porous Ti6Ta4Sn scaffold is thought to be a promising orthopedic implant material by virtue of its excellent biomechanical properties, in vitro bioactivity and biocompatibility highly preferred by osteoblast-like cells. [Copyright &y& Elsevier]

The substructure and texture development during dynamic recrystallization (DRX) of an austenitic Ni–30%Fe model alloy was investigated using hot torsion testing. The current results revealed that the DRX texture was dominated by grains with a low Taylor factor component. This was related to the preferred nucleation and lower consumption rates of these grains during DRX. The substructure of DRX grains was “random” in character and displayed complex subgrain/cell arrangements that largely depended on grain orientation. [Copyright &y& Elsevier]

Abstract: Calcium phosphate (Ca-P) coatings were deposited on Ti substrates by a biomimetic method from m-SBF and 10× SBF, respectively. Comparative study of microstructures and bond strengths of the Ca-P coatings deposited from those different SBFs was carried out. Effect of the surface roughness of the substrates on the bond strength of the Ca-P coatings was also studied. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transformed infrared spectroscopy (FTIR), inductive coupled plasma spectrometry (ICP) and thermogravimetry (TG) were used to characterize the Ca-P coatings. The bond strengths between the coatings and Ti substrates were measured using an adhesive strength test. Results indicated that the ionic concentrations of the SBFs and the surface roughness of the substrate had a significant influence on the formation, morphology and bond strength of the Ca-P precipitates. The induction period of time to deposit a complete Ca-P layer from the m-SBF is much longer, but the Ca-P coating is denser and has higher bond strength than that formed from the 10× SBF. The Ti with a surface roughness of R a 0.64 µm and R z 2.81 µm favoures the formation of a compact Ca-P coating from the m-SBF with the highest bond strength of approximately 15.5 MPa. [Copyright &y& Elsevier]

Understanding the mechanical behaviour of pure titanium (Ti) foam is crucial for the design and development of Ti foam-based load-bearing implants. In this work, pure titanium foam is fabricated by a powder metallurgical process using the space-holder technique with a spacer size of 500 to 800 µm. Experimental data from static compression testing on the Ti foam are presented. The application of theoretical formulae to predict Young's modulus and yield strength of titanium foams is also discussed. A foam with 63% porosity, 87 ± 5 MPa yield strength, and 6.5 ± 1.3 GPa Young's modulus is found to be appropriate for a number of dental and orthopaedic applications. [ABSTRACT FROM AUTHOR]

Abstract: A new method is proposed to quantify progress of dynamic recrystallization in polycrystalline metals during deformation. This approach utilises the stress–strain curve of the material to quantify the progress of dynamic softening. The outcome of this method showed a good agreement with experimental results for alloys of this study. [Copyright &y& Elsevier]

A feasibility study for handling the partial recrystallisation in multi-pass hot deformation where the heterogeneity of microstructure of deformed austenite is inherently accompanied is presented. The proposed model is based on modification of the conventional model in which the microstructure of deformed austenite at each pass is simply taken as being homogeneous during the multi-pass deformation. The usefulness of the modified model has been demonstrated by applying it to a four-pass oval–round (or round–oval) rod rolling sequence. The recrystallised fraction, austenite grain size (AGS) and mean flow stress at each pass computed from the modified model has been compared with those from the conventional model.The result showed that the recrystallisation behaviour and evolution of AGS at a given pass were dependent on the modelling method of the partial recrystallisation in the multi-pass rolling for the case studied. As the rolling speed increased, the difference between the mean flow stresses calculated by the conventional model and the proposed model was gradually larger in accordance with the contribution of partial recrystallisation. [Copyright &y& Elsevier]

Microstructures and mechanical properties of a low carbon steel were studied after plate rolling and bar rolling. Plate rolling is characterized as a monotonic compressive loading, while bar rolling is characterized as a cross-compressive loading. A four-pass plate rolling and bar rolling experiment was designed so that the material experiences the same amount of strain at each pass during rolling. The rolling experiment was performed at moderately high temperatures (450, 550 and 650 °C). The microstructures and mechanical properties of the low carbon steel acquired from the two types of rolling experiments were compared. The results revealed that differences of loading path attributed by monotonic loading (plate rolling) and cross loading (bar rolling) significantly influenced the microstructures and mechanical properties such as yield stress, ultimate tensile stress, strain hardening exponent and elongation of the low carbon steel. [Copyright &y& Elsevier]

The influence of thermomechanical processing (TMP) of a Ti–6Al–4V alloy on the transformation texture and intervariant boundary network were investigated by conventional EBSD mapping along with the five-parameter boundary analysis approach. The texture characteristics of Ti–6Al–4V subjected to deformation in the β regime followed by the β → α martensitic transformation were examined using visco-plastic self-consistent simulation and forward calculation of the transformation texture. Comparison of the simulated and experimental texture characterisitcs revealed that the transformed α ′ texture was dominated by the variant selection associated with substructure development in the β parent phase and the occurrence of specific self-accommodating α ′ variants in the microstructure, promoting the quadrilateral and/or V shape variant arrangement. This resulted in a progressive increase in the 63.26°/ [ 10 ‾ 55 3 ‾ ] intervariant boundaries with the strain increment, at the expense of 60°/ [ 1 1 2 ‾ 0 ]. Moreover, the grain boundary network for all conditions was dominated by the triple junctions (grain boundary network) terminating on 63.26°/ [ 10 ‾ 55 3 ‾ ] and 60°/ [ 1 1 2 ‾ 0 ] intervariants. It is shown that the elastic interactions among the variants during the martensitic transformation is the dominant parameter affecting the grain boundary network, despite the presence of dislocation based variant selection. [ABSTRACT FROM AUTHOR]

Abstract: The indentation slope curve from a spherical indentation on elastic-plastic materials is examined. By comparing it with that of an linear elastic material of the same elastic properties, we found that the start point of plastic yielding for an elastic-plastic material can be easily located from the indentation slope curve. Based on this analysis, a simple but effective method is proposed to measure the plastic yield stress of very small samples from a spherical nano-indentation slope curve. [Copyright &y& Elsevier]

The role of phase transformation mechanism on the development of the grain boundary network in a commercially pure Ti was investigated using five-parameter grain boundary analysis along with an analysis of the triple junctions among intervariant boundaries. High temperature β was subjected to three different cooling regimes (i.e., 175 °C/s, 1 °C/s and 0.02 °C/s) to stimulate shear, diffusion-assisted and pure diffusional β-to-α phase transformation mechanisms, resulting martensite, Widmanstätten, and coarse-grain microstructures, respectively. The phase transformation mechanism appeared to significantly alter the grain boundary network in pure Ti. There was a distinct difference in the misorientation angle distribution among microstructures formed through different phase transformation mechanisms, though the peaks were largely consistent with the Burgers orientation relationship. The 60°/ 1 1 2 ¯ 0 intervariant boundary had the highest population (~60%) in the martensitic/shear transformation, because of a local variant selection mechanism (i.e., three variant clustering) influenced by the transformation strain. However, the local variant selection associated with the transformation strain gradually diminished with a decrease in the cooling rate, leading to a progressive decline in the 60°/ 1 1 2 ¯ 0 population (i.e., the random distribution of intervariant boundaries). The 60°/ 1 1 2 ¯ 0 intervariant boundary had symmetric tilt 1 ¯ 1 0 1 plane characteristics with a low energy configuration in the martensitic microstructure and an asymmetric tilt character in both diffusion-assisted and diffusional transformations. The three-variant clustering during the martensitic transformation significantly enhanced the connectivity of the 60°/ 1 1 2 ¯ 0 intervariant boundaries at the triple junctions, though it became progressively less connected as the mechanism altered towards diffusion-assisted and diffusional phase transformations. Unlabelled Image • Transformation mechanism alter the population and character of α/α intervariants for pure Ti. • Preference of low energy 1 ¯ 1 0 1 intervariants in martensite compared to diffusional microstructure. • The intervariant boundary connectivity were influenced by the transformation mechanism in pure Ti. [ABSTRACT FROM AUTHOR]

• An improved solution of the compression test with integrated barrelling data. • Developed a technique to evaluate a proposed deformation model. • Derived and solved 3 incremental models of BCT profile. • Evaluated and compared the results with those of 2 reference FEA and BCT models. Physical simulation of forming is an analytical-experimental branch of mechanical science. Carefully formulated models and their solutions are essential to interpret the simulation data meaningfully and to understand its underlying phenomena. Oversimplified models of deformation and their associated non-unique closed-form solutions are widespread due to the complex and path dependence nature of plastic deformation, its multi-layered governing equations and boundary conditions. Therefore, it is vital to critically evaluate these models at the kinematic level to ensure a reliable outcome. Incremental Profile Modelling (IPM) is proposed as a technique to integrate free surface geometrical data into the solution to address the path dependence issue. IPM also allows quantification of the solution's worthiness without making a reference to the mass or acting forces involved. The technique relies on calculating an equivalent area for a given solution. The area is estimated simply based on the deforming body's geometry and is compared with that of a numerical solution as the reference. The comparison provides a quick and quantitative assessment of the closed-form solution. To demonstrate the technique, the "Barrelling Compression Test" (BCT) is chosen here as a key example. Three kinematic models of the test are considered and their closed-form solutions are obtained and evaluated using IPM. Also, two reference solutions of the test are presented including those of a finite element model and the conventional Cylindrical Profile Model (CPM). The equivalent areas for the first two models and that of the finite element were in good agreement. The third model rendered an "equivalent area singularity" at the sample's centre, and was concluded to be unsuitable to study BCT. The conclusion was not evident purely based on the model's kinematic solution. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This paper reports on a crucial role of the morphology of intermetallic Al 11 RE 3 phase and Al/Al 11 RE 3 interphase (where RE – Rare Earth) surface area, before plastic deformation, on the electrical and mechanical properties and the thermostability of aluminium alloys. Cast Al-4.5 (Ce + La) alloy samples, processed with and without spheroidization treatment (ST), were subjected to high pressure torsion (HPT) at room temperature (RT) followed by annealing at 230 °C, 280 °C and 400 °C for 1 h. It is demonstrated, that the changes of initial alloy structure (particles shape/size) and the decrease of interphase surface area affect the distribution of intermetallic particles after HPT, the distribution of ultrafine grains and the dislocation density, as well as the formation of a supersaturated solid solution of Ce and La in aluminium. The optimal combination of strength (ultimate tensile stress (σ UTS) 430 MPa) and conductivity (55.9% International Annealed Copper Standard, IACS) was obtained after ST, HPT and an annealing temperature of 230 °C. Image 1 • Influence intermetallic morphology on structure and properties of Al alloys is studied. • The alloys were subjected to severe plastic deformation in different initial state. • HPT of Al-4.5(Ce,La) alloy results in supersaturated solid solution formation. • Application of pre-HPT heat treatment prevents the solid solution formation during HPT. • The diffusion of Ce and La in Al is provided by extra vacancy concentration. [ABSTRACT FROM AUTHOR]

In the current study, the effect of deformation in the non-recrystallization region on the characteristics of interphase precipitation was extensively studied in a Ti-Mo steel. The present observation revealed a novel mechanism affecting the interphase precipitation characteristics during an austenite-to-ferrite transformation, as a result of the thermomechanical processing. The hot deformation primarily led to the fragmentation of an austenite grain interior through the formation of elongated dislocation walls, locally deviating the orientation within a grain. Relatively coarse strain-induced precipitates were initially formed on the dislocation walls upon cooling. During the isothermal austenite to ferrite transformation, the interphase precipitation took place on the advancing austenite-ferrite interface front. This was similar to the strain-free condition, though the alignment of planar rows was abruptly altered while encountering the microband walls due to local orientation change at either side of a given microband. In addition, the deformation reduced the planar spacing of interphase precipitates up to a given strain (i.e., ∼0.3), beyond which it became nearly constant. This was due to the saturation of dislocation density within austenite above a certain strain and/or the consumption of alloying elements through the strain-induced precipitation formed on the microbands prior to the austenite to ferrite transformation. Image 1 [ABSTRACT FROM AUTHOR]

Abstract As one of the most mature titanium alloys, Ti6Al4V is widely used in many critical aerospace applications. However, the flow behavior of this alloy cannot be easily predicted using general computational models, mainly due to the existence of various microstructural morphology in titanium alloys and relatively complex deformation mechanisms during hot deformation. Principally, the variation in initial grain morphology and grain size/plate thickness significantly influences microstructural evolution during hot working, thus leading to dissimilar work hardening and related softening behaviors. In the current study, a microstructural based Estrin Mecking (EM) +Avrami model was developed and used to model the deformation behavior of Ti6Al4V alloy with different initial grain morphologies (i.e. equiaxed vs martensitic) during simulative hot compression testing in the α + β phase region. Herein, the effect of initial grain size was considered as a function of Hall-Petch strengthening, where experimental validation revealed very good accuracy on predicting the work hardening behavior, peak stress, peak strain and flow softening with varying grain morphologies. In addition, the current model was extended to predict the material flow behavior of Ti6Al4V alloy during bulk metallic deformation (i.e. forging) in 3D as an FEM based simulation tool. [ABSTRACT FROM AUTHOR]

Highlights • Two types of austenite morphologies, equiaxed (EQ) and Widmanstätten (W), were produced. • W-A showed a larger degree of coherency at δ/γ interfaces relative to the EQ-A. • W-A showed unexpected propensity to the formation of secondary precipitates. • Higher extent of interface area and unstable δ were found to contribute to this behaviour. Abstract Two types of austenite morphologies, equiaxed and Widmanstätten, were produced through different phase transformation routes to evaluate the critical factors affecting the intergranular corrosion susceptibility in a 2205 duplex stainless steel. These distinct austenite morphologies behaved quite differently in secondary phase precipitation on exposure to sensitization temperature. Although the Widmanstätten microstructure was found to have a larger degree of coherent ferrite/austenite interface area compared with the equiaxed one, it showed a higher degree of sensitization. It was clarified that, in addition to the ferrite/austenite interface coherency, the extent of an interface area and presence of un-stable ferrite also play prominent roles in intergranular corrosion susceptibility. [ABSTRACT FROM AUTHOR]