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Severe plastic deformation processes involve large grain rotations due to the action of different modes of plastic deformation and other microstructural changes which lead to characteristic texture formation. The present review deals with the evolution of texture during the most important severe plastic deformation processes, namely Equal Channel Angular Pressing (ECAP), High Pressure Torsion (HPT), Friction Stir Processing (FSP), Accumulative Roll Bonding (ARB) and Multi-Axial Forging (MAF). First three of the processes are shear based, while the latter two are plane-strain based. The textures formed during ECAP are visually different from simple shear textures due to (i) the inclination of the shear plane, (ii) additional contribution of non-shear based deformation. The relative intensities of texture components are function of deformation micro-mechanisms, amount of straining and configuration of the strain path. The texture evolved during HPT is very similar to simple shear texture, with additional consequences of microstructural changes that occur due to very large deformations. The textures formed in FSP process also resemble shear textures. On the other hand, texture evolution during ARB and MAF can be described using plane strain deformation. The present review deals with texture evolution during severe plastic deformation as a function of nature of processes and type of materials.

Molecular dynamics (MD) and single-crystal plasticity finite-element method (CP FEM) are approaches used to simulate the micro-machining process. At such small-length scales, anisotropic behaviour of material becomes important; the two methods can essentially capture it. Therefore, it is important to understand the fundamental principle behind these methods as well as their capabilities and limitations in order to select the scheme to simulate the micro-machining process. In this paper, the fundamentals of MD and CP FEM are introduced in brief. The applicability of the respective method is further illustrated with the help of examples from the literature. Thereafter, the two methods are compared and discussed in terms of their various aspects and capabilities. This discussion should enrich the reader and assist their choice of an appropriate simulation method.

BiCuSeO is a promising thermoelectric material not only because of its good thermoelectric properties, but also earth abundant constituents. In this report, Pb and Na have been simultaneously doped at the Bi site of BiCuSeO. Doping Pb is beneficial for the Seebeck coefficient whereas doping Na maintains the hole mobility. Both the dopants increase the carrier concentration and reduce the thermal conductivity by point-defect scattering. The samples with nominal composition Bi0.985-xNa0.015PbxCuSeO ( x=0.00, 0.04, 0.06 and 0.08) were prepared using two-step solid-state synthesis. The X-ray diffraction pattern reveals a small amount of Bi2O2.5 phase (

In an expansive field of metals, magnesium has been trending of late in automobile, aerospace, defense, sports, electronic and biomedical sectors as it offers an advantage in lightweighting. In the realm of Mg-based materials, Mg nanocomposites have a good combination of specific strength, thermal and damping properties, but lack a high ductility and do not typically undergo a large amount of uniform elongation. The current work bridges this gap by reporting a magnesium nanocomposite (Mg�1.8Y/1.5Y 2 O 3 ) that exhibits a significantly high tensile ductility of 36. Microstructural characterization of the nanocomposite revealed that the striking presence of micron-Mg�Y phases and nano-Y 2 O 3 particles in matrix led to a bimodal particle distribution which affected the dynamic recrystallization mechanism. It was also observed that the addition of Y 2 O 3 nanoparticles weakened the texture of nanocomposite. The dominating influence of texture weakening over other mechanisms (grain refinement and alleviated micro-strain) on the plastic deformation/ductility of the nanocomposite is highlighted, and the contribution of nanoparticles toward the enhancement of ductility is ascertained. In contrast to the previous studies where Mg-based nanocomposites are known to have improved strengths, this approach can be used to develop magnesium nanocomposites that are exceptional. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

International audience; The High Pressure Tube Twisting (HPTT) process was first proposed in 2009 as an efficient new Severe Plastic Deformation (SPD) process. Since then it has been successfully applied on many different materials and the results have been reported in several publications and thesis works. The purpose of this overview is to present and evaluate the main results of the published papers and thesis works and also to present new contributions. Special attention is given to the strain gradient which appears in the tube wall for which a new empirical formula is presented.

Deformation mechanisms of cold drawn and electropolished nickel microwires are studied by performing in-situ monotonous and cyclic tensile tests under synchrotron radiation. X-ray diffraction tests allow probing elastic strains in the different grain families and establishing a link with the deformation mechanisms taking place within the microwires. The measurements were carried out on several microwires with diameters ranging from as-drawn 100 µm down to 40 µm thinned down by electropolishing. The as-drawn wires exhibit a core-shell microstructure with fiber texture dominant in core and heterogeneous dual fiber texture and in the shell. Reduction of specimen size by electropolishing results in a higher yield stress and tensile strength along with reduced ductility. In-situ XRD analysis revealed that these differences are linked to the global variation in microstructure induced by shell removal with electropolishing, which in turn affects the load sharing abilities of grain families. This study thus proposes a new way to increase ductility and retain strength in nickel microwires across different diameters by tuning the microstructure architecture.

Chalcopyrite (CuFeS2) is an earth abundant, non-toxic, thermoelectric (TE) material with a high Seebeck coefficient of -480 µV K−1 at 300 K. But its TE performance is hindered due to low electrical conductivity (∼ 29 S cm−1 at 300 K) and high thermal conductivity (∼ 6.5 Wm−1K−1 at 300 K). Pristine CuFeS2 and Co,Se substituted compounds were prepared by solid state method. Powder X-ray diffraction confirmed the formation of the CuFeS2 phase (ICSD#2518). The transport properties were measured between the temperature 350 and 673 K. The Seebeck coefficient (S) was negative for the pristine sample indicating n-type conductivity. Due to the deficiency of copper in the substituted samples, minority charge carriers dominated, and S was ∼50 µV K−1 from 350 to 550 K. After 550 K, S becomes negative indicating that electrons are the majority charge carriers. The electrical conductivity is higher for the substituted samples compared to the pristine. The total thermal conductivity (κ) followed a T−1 trend, for all the samples due to Umklapp scattering. The isovalent substitution of Se for S helped in reducing the κl. The figure of merit of 0.018 at 673 K was obtained for the substituted samples which was higher than the pristine sample (∼ 0.008 at 673 K).

High energy synchrotron radiation was used to perform an in-situ diffraction experiment in medium Mn Fe-6Mn-0.5C-1Al alloy to study the elemental partitiong and austenite phase evolution at different heating, holding and cooling stages. It has been observed that austenite phase fraction increases at inter-critical annealing temperature significantly and it remains stable at room temperature. Austenite phase stability at room temperature is due to rapid partitioning of Mn and C during annealing. The relative change in d-spacing (Δd/d) during heating-cooling indicates partitioning of alloying elements during inter-critical annealing.

Present work deals with modification of lamellar microstructure of a γ – TiAl alloy to globular concerning α2 phase. For this investigation, cast Ti-48Al-2Cr-2Nb alloy was subjected to cyclic heat treatment. This cycle was consisting of heating and cooling alternatively to order – dis-order (α2 ↔ α) regime. Thermal cycles led to the change of lamellar α2 phase to globular. Additionally, with time of globularisation, average micro-hardness was identified to be decreasing at the expense of grain coarsening with respect to γ and globularised α2 phase. Phase percentage of both phases was observed to be stabilizing with cycling time. Based on phenomena of globularisation with time, a possible mechanism was designed for understanding the mechanism of globularisation.

The combined effects of Ba-filling the voids and GaSb nanophase incorporation in the matrix of Co4Sb12 have been studied for thermoelectric properties. High energy ball-milling was used to disperse GaSb in Ba0·2Co4Sb12. A slight off-stoichiometry between Co and Sb generated CoSb2 and CoSb phases. Electron back-scattered diffraction showed nanocrystalline (50–200 nm) GaSb grains uniformly distributed on the matrix along with a few large grains (1–3 μm). The low electrical resistivity (ρ) of Ba0·2Co4Sb12 can be attributed to the +2 oxidation state of Ba. The increase in ρ of composites occurred due to the enhanced scattering of charge carriers at interfaces. No significant change in Seebeck coefficients was found in composites. The simultaneous effect of anharmonicity induced by Ba-filler in the voids and the enhanced interfaces between GaSb and the matrix reduced lattice thermal conductivity and brought about an improvement in zT from 0.75 to ~1.0 for (GaSb)0.4+Ba0·2Co4Sb12 at 773 K.

In recent years electron beam melting has been explored to establish its suitability for product manufacturing as this additive manufacturing route offers advantages which are not achieved in other similar processes. This paper focusses on the prime issues associated with 316L manufactured using electron beam melting. Location dependent microstructure and strain accumulation is found to be completely different at central and peripheral regions in a particular layer. Coarser grains as well as lesser amount of strain value is observed at central region when compared to periphery. Crystallographic texture at centre is seen as intensified parallel to build direction whereas it is weak and relatively scattered ( and both) for periphery. BD parallel plane gives a glimpse of available energy as well as repeated thermal cycling as long elongated grains were observed and lowest strained region, depicting the high anisotropic structure altogether.

Despite a tremendous amount of research to understand the evolution of microstructural and texture changes during deformation, there is still a need for further deep insight into it. The most used deformation process underuse in industries is the rolling of material. Stacking fault energy is the most critical material property, which governs the deformation behavior. In the present study, the microstructure and texture changes of a high SFE material (pure nickel) during cold rolling was investigated. The objective is to find criteria for the change of orientation of a particular grain as rolling proceed. Pseudo-in-situ rolling was done through which the shape, orientations, and neighbors of each grain could be tracked as a function of rolling reductions. It was found that orientations of some grains remain stable after a large reduction and do not develop sub-grains within it, whereas orientations of some grains change drastically at a very low deformation level along with the evolution of a large number of sub-grains.

In the present study, the evolution of microstructure, crystallographic texture and their influence on mechanical properties of the Al–Li alloy, AA2195 has been studied. A novel hybrid processing route involving warm multi-axial forging (MAF) and subsequent warm rolling was employed. Different rolling procedures were followed to obtain optimal microstructure and properties. The processing conditions significantly influenced the course of evolution of microstructure and texture. A variation in tensile properties as a function of angle from RD for the differently processed samples was noticed. The tensile properties were closer to isotropic case for the samples deformed using a combination of MAF with cross rolling. By controlling grain size and texture through optimal processing, it was possible to achieve isotropic tensile properties in the AA2195 alloy. The processing conditions have also led to enhancement in strength, which has been attributed to grain boundary strengthening, precipitation strengthening and dislocation strengthening.

In the present work, attempts have been made to control the yield strength anisotropy in an Al–Cu-Li alloy by implementing a novel processing route combining multi-axial forging (MAF) and rolling with an aim to weaken the texture. It has been observed that continuous destabilization of deformation texture during MAF results in weakening of texture. Further weakening of texture could be achieved upon post MAF cold cross rolling, which has been attributed to (i) the geometry induced shear in the roll gap, and (ii) the change in strain path during rolling. Such a weak texture is in contrast to strong Brass-type texture, generally observed in these alloys. Further annealing in the solution treatment regime led to even more weakening of texture. Uniaxial tensile tests along different directions of the as-processed sheets confirmed the weak dependency of yield strength on orientation of tensile axis.

In the friction stir welding (FSW) of dissimilar materials, the weld nugget exhibits composite properties and is composed of hard particles (high-strength material) distributed in a soft matrix material. The distribution of these particles influences the properties of the weld. Therefore, it is useful to characterize the deformation and fragmentation of the high-strength material from which they originate. In the current study, FSW of aluminum (Al) to titanium (Ti) was performed and a new technique was introduced to remove Al from the post-weld sample to characterize the deformation and fragmentation of Ti in the weld nugget. The post-weld sample showed that Ti particles were inhomogeneously distributed. It was understood that the plastic deformation of the Ti depends on its location of the weld. A detailed investigation revealed a number of fracture zones in titanium. A systematic analysis revealed the evolution of twins in Ti in the thermos-mechanically affected zone (TMAZ), whereas no-twins and recrystallized grains were noticed on the Ti flake that was consolidated in the weld nugget. The X-ray computed tomography (XCT) showed that Ti flakes were subjected to deformation and bending. Furthermore, it was noticed that the width of the flakes was not identical along their length and that the flakes were broken at the middle region into two parts. It can be concluded that Ti, at the interface and as flakes, was subjected to severe deformation at a lower homologous temperature that leads to the formation of adiabatic shear bands (ASBs). The local evolution of temperature within the ASBs was much higher than the general weld temperature, leading to the recrystallization of Ti at the interface. Moreover, ASBs are prone to crack nucleation and propagation; hence, particles with different morphology and sizes were noticed in the nugget zone. The distribution of particles was inhomogeneous due to variation in the particle size and complex mechanical mixing. The distribution of particles varied with location across the weld nugget. A homogeneous mechanical mixing was noticed at the center of the weld nugget due to complex material flow and distribution of finer particles. With this understanding of the deformation and fracture mechanism of titanium during dissimilar FSW of Al to Ti, it is possible to engineer the developed composites and/or weld nuggets of dissimilar materials to achieve the required combination of mechanical properties.

Deformation mechanisms in nanocrystalline Ni-x wt% Co alloys (x = 0, 20, 40, 60), having stacking fault energy values from high to low, have been investigated with regard to the evolution of microstructure and texture during room temperature rolling. In all the materials, no new texture peak appears until 20% thickness reduction and the texture is similar to initial fiber texture, which indicates that grain boundary-mediated deformation mechanisms are more active. The development of characteristic copper-type and brass-type rolling textures is visible beyond 40% reduction. High SFE materials, namely pure Ni and Ni-20Co alloy, develop a copper-type texture at large reduction, whereas in low SFE Ni-40Co and Ni-60Co alloys, the texture is close to brass-type. The evolution of copper-type texture is attributed to the activity of 1/2{111} type dislocations and cross slip in nanocrystalline grains, which is aided by deformation-driven grain growth. Crystal plasticity simulations suggest that the evolution of brass-type texture evolution in low SFE nanocrystalline alloys is due to 1/6{111} type partial dislocation slip. The activity of partial slip is promoted by the suppression of grain growth and cross slip in high cobalt containing alloys. The evolution of deformation texture and microstructures in nanocrystalline nickel cobalt alloys is governed by the combined effects of grain size and SFE. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We report a rare experimental evidence of an exceptional increase in grain-boundary diffusion-controlled growth kinetics of product phase by grain-refinement due to minor alloying. Ti-addition during growth of V3Ga superconductor by coupling V and Cu(Ga)-solid solution by bronze process increases the critical current density (Jc) significantly. In this manuscript, the exact role of Ti-addition is studied based on systematic and quantitative diffusion-couple experiments that mimic the bronze-method. Metallurgical aspects like microstructural features and growth mechanism are assessed critically. Results are compared when Ti is added either to V or Cu(Ga) and to both for a fixed Ga content. Ti-addition to Cu(Ga) compared to V increases growth kinetics of V3Ga more significantly. Quantitative EPMA-analysis indicates that a mixture of Ti-free and Ti-containing V3Ga phase grows when Ti is added to V. Small precipitates grow along with Ti-containing V3Ga when Ti is added only to Cu(Ga). TEM-study indicates that these precipitates are rich in V and Ti. Much finer grains found in the precipitate-containing region lead to higher growth kinetics due to grain-boundary diffusion. EBSD-analysis shows equiaxed grains and relatively random in orientation because of alloying. This study indicates that Ti-addition to Cu(Ga) is most effective considering metallurgical aspects that influence Jc. Keywords: Superconductor material, Microstructure, Grain size distribution, Grain boundary diffusion, Microtexture

We report the epitaxial growth of Ni2MnGa thin films on MgO(100) substrate deposited at elevated temperature using direct current magnetron sputtering. The structural and texture analysis of as deposited film reveal the (010) crystallographic orientation with seven modulated martensite phase and an epitaxial relationship of Ni2MnGa(010){101} parallel to MgO(001){110} between the film and the substrate. The crystal quality of the films was analysed by performing symmetric and asymmetric rocking curve measurements and dislocation density for screw and edge dislocations is determined to be 6 x 10(9) cm(-2) and 3.45 x 10(10) cm(-2), respectively. The presence of micro-twins at an angle of 45 degrees with respect to growth direction and seven modulated nano-twins formed by adaptive modulation has been observed with transmission electron microscopy investigations. The magnetic measurements indicates magnetic field induced reorientation of martensitic variants, strong magneto-crystalline anisotropy and a very high saturation magnetization (I-s) of 61 emu g(-1) in the film. (C) 2016 Elsevier Ltd. All rights reserved.

In this paper, a fine distinction between the role of strain-paths on the evolution of mechanical properties has been reported. Commercially pure (CP) titanium plates were subjected to hot rolling of 90% reduction in thickness through different strain-paths such as unidirectional rolling (UDR), multistep cross-rolling (MSCR) and reverse-rolling (RR). It was observed that the sample rolled through RR had higher mechanical properties (both yield strength and ductility) followed by the samples rolled through MSCR and UDR respectively. It was further observed that the RR sample had higher stored energy followed by MSCR and UDR samples which eventually controls the evolution of microstructure and hence defines the mechanical properties.

Highly oriented Ni–Mn–Ga thin film with multiple variants and room temperature orthorhombic martensite structure were prepared on a single crystalline Al2O3 $\left({11\bar 20} \right)$ substrate by DC magnetron sputtering. X-ray diffraction and rocking curve measurements reveal the film as (202)7M oriented with an excellent crystal quality (Δω = 1.8°). Spot-like pole figures indicate that the Ni–Mn–Ga film grows with a strong in-plane preferred orientation. An in-depth analysis of the measured pole figure reveals the presence of a retained austenite phase in the film. Two phase transformations, MS ∼345 K and TC ∼385 K, are observed and are attributed to first order structural transformation from cubic to orthorhombic, and second order phase transformation from ferromagnetic to paramagnetic, respectively. In situ high temperature x-ray diffraction measurements provide a clear indication of a thermally-induced martensite ↔ austenite reversible structural phase transformation in the film. The presence of martensite plates with seven modulated orthorhombic structure and adaptive nano-twins are some of the important microscopic features observed in the film with transmission electron microscopy investigations.

The micro-mechanisms associated with the evolution of deformation texture in nickel and nickel-cobalt alloys, with stacking fault energy (SFE) ranging from high to low, has been investigated. Pure nickel and nickel-20 wt.% cobalt alloy, which are high SFE materials, develop a characteristic copper-type texture, which is attributed to dislocation slip. In the medium SFE nickel-40 wt.% cobalt alloy, the texture is copper-type up to 95% reduction; however, subsequent reduction to 98% causes the texture to shift towards brass-type. Microstructural examination suggests that the occurrence of Cu-type shear bands (SBs) preferentially in the Cu {1 1 2}-oriented grains has led to this texture transition. In nickel-60 wt.% cobalt alloy, which is a low SFE material, texture is brass-type from the early stages of rolling. Deformation mechanisms show a gradual transition from deformation twinning to Bs-type SBs, as a function of strain. The strength of the final texture is a synergistic effect of twinning and shear banding. The absence of Cu component during the process of brass-type texture evolution goes against Wassermann's prediction of texture transition. A modified theory for the formation of brass-type texture is proposed.

Commercially pure (CP) titanium plates were subjected to hot rolling down to 50%, 70%, 80% and 90% reduction in thickness through unidirectional rolling (UDR), multistep cross-rolling (MSCR) and reverse-rolling (RR). It was observed that the samples had dominant basal texture (basal fiber) irrespective of the reduction percentages and the modes of rolling. Two types of twins, {11̅02} type tensile twins and {12̅12} type compressive twins, were observed in the microstructures. These twins were present in more abundance in the samples processed under MSCR and RR conditions, particularly for 50% reduction in thickness. A decreasing trend of average grain size, average grain orientation spread and fractions of twin boundaries as well as low angle grain boundaries was observed as a function of deformation for the UDR and RR strain paths. The MSCR samples have shown a deviation from the trend, which has been attributed to dominance of twinning in the deformation mechanism. Keywords: CP-titanium, Hot rolling, Strain paths, Crystallographic texture, Deformation twinning

The hot deformation behavior of Nb–1 wt.%Zr alloy was studied using uniaxial compression tests carried out in vacuum to a true strain of 0.6 in the temperature range of 900 to 1700 °C and the strain rate range of 3 × 10−3 to 10 s−1. The optimum regime of hot workability of Nb–1Zr alloy was determined from the strain rate sensitivity (m) contour plots. A high m of about 0.2 was obtained in the temperature and strain rate range of 1200–1500 °C and 10−3 to 10−1 s−1 and 1600–1700 °C and 10−1 to 1 s−1. Microstructure of the deformed samples showed features of dynamic recrystallization within the high strain rate sensitivity domain. Compared to the study on Nb–1Zr–0.1C alloy, Nb–1Zr showed a lower flow stress and an optimum hot working domain at lower temperatures. In the 1500 to 1700 °C range the apparent activation energy of deformation for Nb–1Zr was 259 kJ mol−1, the stress exponent 5, and the activation volume about 200 to 700 b3. Keywords: Nb–1Zr alloy, Hot deformation, Strain-rate sensitivity, Dynamic recrystallization

Equal channel angular pressing was carried out on Al–Mg alloys to study the effect of Mg addition on the microstructure, texture and strength after severe plastic deformation by 8 passes of equal channel angular pressing (ECAP) through route Bc. The increase in Mg content enhanced the propensity of continuous dynamic recrystallization and simultaneously decreased the average grain size of the alloy. The microstructure and local texture was heterogeneous across the billet thickness for all the samples, irrespective of composition. All the samples showed a shear-type bulk texture generally observed in face-centred cubic metals with strong BE/‾BE components. The weakening of the texture with increase in Mg content is attributed to the substructure evolution during the ECAP process. The grain size and dislocation density have been determined by X-ray diffraction line profile analysis. The experimentally determined yield strength of the ultrafine grained samples can be explained by a combination of solid solution, dislocation and grain size strengthening, the latter being predominant.

In this investigation we report the formation of a graded microstructure in copper/tantalum ultrafine grained (UFG) multi-layered composite fabricated by cross accumulative roll bonding (CARB) process at high temperatures. The microstructure, micro-texture and bulk texture evolution in the copper/tantalum composite was established. A gradient microstructure develops along the thickness of the specimen during the CARB process. The fragmentation of tantalum in between copper layers and the grain refinement with evolving passes has been explained. The deformed copper layers show rotated cube texture and deformed tantalum layers show cube texture with γ-fibre. The overall texture of copper/tantalum composite weakens after the process of ARB; copper undergoing texture randomization post annealing. The crucial role of interfaces on the evolution of texture is demonstrated. The microstructural gradient in the specimen possess equiaxed, lamellar as well as large deformed grains with tantalum's grain size being in the scale of 200 nm. The correlation of microstructural gradient with orientation relationship (OR) between copper and tantalum layers was studied, confirming higher misorientation in OR at regions under high strain. Dynamic recrystallization taking place at the copper/tantalum interface has been elaborated with the aid of microtexture analysis.

A comprehensive investigation was carried out to explore the micro-mechanisms associated with the evolution of deformation microstructure and texture in Ni-Fe alloys during rolling. X-ray diffraction, electron back-scatter diffraction (EBSD) and Mossbauer spectroscopy as well as simulation methods involving crystal plasticity and molecular dynamics simulations were used to explore the mechanism of evolution. Pure Ni, Ni20wt.%Fe and Ni40wt.%Fe were rolled to true strain 3.0, following two different strain paths. Unidirectionally rolled Ni20wt.%Fe and Ni40wt.%Fe alloys show copper type texture, similar to that of pure Ni. By contrast, the cross rolled samples show the development of α-fibre along with A {110} and cube {100} orientations. Both Ni20Fe and Ni40Fe exhibit extensive shear banding in UDR as well as CR conditions, unlike pure Ni, which has been attributed to the appearance of two short-range ordered phases, Ni3Fe and NiFe. In case of UDR, the nature of shear banding is different in Ni20Fe and Ni40Fe alloys, while after CR both the alloys show similar microstructures displaying higher fraction of shear banding compared to UDR. Simulation results have indicated that larger number of slip systems are activated in case of CR compared to the UDR samples that leads to the formation of a weaker texture in the former. Some strain free grains have been observed near the shear banded regions, indicating that an extended recovery mechanism could be operative in Ni20Fe and Ni40Fe. This phenomenon was more pronounced when the fraction of shear bands was more.

Two titanium aluminide (TiAl) based compositions with different niobium (Nb) contents, namely Ti–45Al–5Nb-0.2B-0.2C and Ti–45Al–10Nb-0.2B-0.2C, have been investigated for their hot deformation response. Prior to deformation, microstructural features were modified by a specially designed thermal treatment. The modified microstructures were intended to be equiaxed to facilitate the deformation response. Deformation responses of materials with modified microstructures were examined using isothermal hot compression tests. Strain rate sensitivity maps were generated from the stress-strain curves and suitable domains for optimal processing were identified. The strain rate sensitivity maps show that the workability of the alloys decreases with increasing strain rate and decreasing temperature. An increase in the proportion of dynamically recrystallized grains, which is indicated by deviation from the ideal orientation relationship between the phases, corresponds to the regions of high strain rate sensitivity. The processing domain for the alloy Ti–45Al–5Nb-0.2B-0.2C has been identified within the temperature range 1075 °C–1200 °C at the strain rate 0.1 s−1, whereas for the Ti–45Al–10Nb-0.2B-0.2C alloy, the temperature range of 1125 °C–1200 °C has been found to be most suitable processing domain at the same strain rate.

This study investigates the exact state of deformation in single point incremental forming (SPIF) and double-sided incremental forming (DSIF) techniques using experimental observations of texture evolution coupled with a multiscale simulation of the processes. The texture evolution was investigated for different sets of forming parameters such as vertical displacement, wall angle and tool diameter. It was observed that difference in crystallographic texture due to change in tool diameter and vertical displacement was marginal. However, significant difference in texture evolution was observed upon changing the wall angle. Further analysis of crystallographic texture revealed that role of through thickness shear (TTS) is limited in case of DSIF process compared to SPIF process. Numerical simulation of SPIF process via finite element method was successful in capturing the contribution from TTS in SPIF process. Based on insights obtained from finite element calculations, Visco-Plastic Self-Consistent simulations were carried out which were successful in predicting the experimental texture. Finally, the effect of different incremental forming techniques on the mechanical properties of the formed components was studied. The observed anisotropy in yield strength was explained based on the inverse of average Schmid factor. Lankford parameter and yield locus were also estimated from the experimental textures to understand the feasibility of incremental forming at different wall angles.

In the present study, the evolution of microstructure, texture and high-temperature mechanical behavior of the additively manufactured (AM) eutectic high entropy alloys (EHEA) AlCoCrFeNi2.1 have been investigated. The material was manufactured through laser engineered net shaping (LENS) process. The microstructural investigation revealed constituent phases consisting of dendritic and eutectic features, with the phases having ordered FCC (L12) and BCC crystal structures. The phase fraction of L12 was more across the build (X) face and that of the BCC was more along build plane (Z face). In both the phases, nickel constituted the base element with L12 phase being deficient in Al and the BCC deficient in Cr and rich in Al. The stability of L12 phase was attributed to Co, Cr, and Fe with near equiatomic distribution. Kurdjumov-Sachs (KS)orientation relationship was followed between the ordered L12 and BCC phases along and across the build-up direction. Strain partitioning was observed more in the BCC phase than in the L12 phase during uniaxial compression at all temperatures. Difference in hardness was observed along Z and X directions which further resulted in yield anisotropy during compression test at room temperature. High-temperature compression tests at temperatures 400 °C, 600 °C, 700 °C, and 800 °C revealed that the yield strength increased from room temperature till 400 °C and then started decreasing till 800 °C.

During dissimilar Friction Stir Welding (FSW) of titanium (Ti) to aluminum (Al), particles of titanium are inhomogeneously distributed in the aluminum matrix, in the weld nugget. The Al/Ti interfaces are the potential zones for intermetallic formation. The inhomogeneous distribution of Ti particles and intermetallic particles can have a negative impact on the mechanical properties of the weld. The objective of the present investigation is to highlight the mechanism of such inhomogeneity in the distribution and formation of intermetallics within the weld. In the present investigation, FSW of Al to Ti was carried out in butt-weld configuration and microstructure across the weld was characterized using Scanning Electron Microscopy (SEM) and X-ray Tomography (XCT). Results from the weld nugget showed three regions of Ti particle distribution, variation in their fragmentation and chemical composition across the Al/Ti interfaces when investigated from top to bottom of the weld. Such variations were correlated with conventional strain rate and temperature variation in the weld nugget. Detailed analysis of microstructure in the weld nugget illustrated that both titanium and aluminum undergo dynamic recrystallization. However, the mechanisms leading to such microstructural evolution were different. Recrystallization in titanium occurred due to low-temperature deformation and evolution of adiabatic shear bands whereas dynamic recrystallization in aluminum was attributed to its high stacking fault energy. The present results and mechanism can be useful in further development of the weld nugget in dissimilar FSW and development of composite by friction stir processing with homogeneous microstructure and superior mechanical properties.

Surface mechanical attrition treatment (SMAT) is recognized as a surface severe plastic deformation (SPD) method that is effective in improving the surface-dependent mechanical and functional properties of conventional metallic biomaterials. In this study, we aimed to systemically investigate the effect of SMAT on the physical, electrochemical, tribological and biological performances of a newly developed low modulus β Ti-Nb-Ta-O alloy with two different microstructures, namely, single phase β-treated and dual phase β + α aged. The microhardness results showed considerable hardening for the β-treated condition due to formation of deformation substructures; that was associated with increased corrosion resistance resulting from a stronger and denser passive layer on the surface, as revealed by Tafel polarization, impedance studies and Mott-Scottky plots. The wear volume loss during fretting in serum solution was found to decrease by 46% while friction coefficient decreased only marginally, due to presence of a harder and more brittle surface. In the β + α condition of the alloy, minimal hardening was observed due to coarsening of the precipitates during SMAT. However, this also reduced the number of α-β interfaces, which in turn minimized the tendency for galvanic corrosion resulting in lower corrosion rate after SMAT. Wear resistance was enhanced after SMAT, with 32% decrease in wear volume loss and 21% decrease in friction coefficient resulted due to improved ductility on the surface. The attachment and growth of osteoblasts on the alloys in vitro were not affected by SMAT and was comparable to that on commercially pure Ti. Taken together, these results provide new insights into the effects of surface SPD of low modulus β- Ti alloys for orthopedic applications and underscore the importance of the initial microstructure in determining the performance of the alloy.

In the dissimilar Friction Stir Welding (FSW) of aluminum to titanium, a large fraction of titanium particles is inhomogeneously distributed in the weld nugget and their distribution is highly complex. Such a distribution can have an immense influence on the grain stability of the weld nugget, which decides its mechanical properties at the high temperatures experienced in critical applications. The present investigation highlights the variation in grain structure at the top surface and center of the weld nugget. The results show that the microstructure at the surface of the weld contains a higher fraction of fine titanium particles, refined grains of aluminum and high-angle grain boundaries, and a lower intensity of shear texture components when compared to the center of the weld nugget. The variation in the grain stability of the weld was correlated with the qualitative variation in the strain rate and temperature in the weld. It is proposed that the formation and distribution of a high fraction of fine titanium particles results in superior grain stability of aluminum at the surface of the weld due to arrest of the grain boundary mobility against grain growth. This mechanism and methodology can be applied in developing metal matrix composites with superior mechanical properties as well.

Dwell sensitivity of titanium alloys at ambient temperature (~250 C) is a well-known phenomenon, although the question about the exact micromechanical reasons responsible for this still remains open. In this work, the normal and dwell fatigue response of a near-alpha titanium alloy, IMI 834, is studied. Samples with three different microstructures, namely, fully lamellar, fully equiaxed and bimodal, are evaluated for their dwell fatigue behaviors. A reduction in fatigue life by at least an order of magnitude is seen in all the three microstructures. Large plastic strain accumulation (almost equal to the monotonic ductility) was observed during the dwell fatigue loading condition and this is held responsible for this large debit in fatigue life. The normal fatigue lives decreased in the order, bimodal > fully equiaxed > fully lamellar, while the dwell fatigue lives decreased in the order, fully equiaxed > fully lamellar > bimodal. Bimodal microstructure showed a dwell fatigue debit of 17, while fully lamellar and fully equiaxed showed a debit of 9 and 10, respectively.

This investigation reports an unusual effect of hold time (up to 10seconds) on retardation in the growth of creep-fatigue small cracks at 550 degrees C in Grade 91 steel. The observed phenomenon was interpreted by elucidating multiple processes that are active in the plastic zone at the crack tip. To this effect, microstructural and mechanical responses of the crack tip plastic zone were compared with the mechanical and microstructural responses during low cycle fatigue/creep-fatigue. It is proposed that the stress relaxation that occurs during the hold time can reduce the stress intensity in the plastic zone of crack tip thus, contributing to retardation in the small crack growth rate. Aside from stress relaxation, stress intensity in the crack tip can be further reduced by the phenomenon of cyclic softening that occurs because of plasticity-induced microstructural coarsening. Separately, the contribution of oxidation-induced crack tip shielding is also considered to explain the observed effects of hold time on crack growth rates. Taken together, a combination of stress relaxation, enhanced rate of cyclic softening, and higher degree of oxidation with the introduction of a hold time is demonstrated to be responsible for reduction in the crack growth under creep-fatigue conditions.

The most important issue associated with dissimilar welding is the formation of detrimental intermetallics and consequent reduction in mechanical properties of the weld. It was expected that addition of an interlayer would modify the pattern of the intermetallic formation. The present investigation deals with Friction Stir Welding of aluminum (Al) to titanium (Ti) in presence of niobium (Nb) interlayer. X-ray Computed Tomography results highlighted that fine particles of both Ti and Nb are homogeneously distributed. Large Ti particles are substantially fragmented whereas large Nb particles remain as flakes. Microstructural features of the nugget zone indicated a complex mixing of materials. Jointing had been perceived through elemental diffusion at the interfaces of Al/Ti and Ti/Nb. However, Nb restricted the reaction between Al and Ti, and acted as an efficient interlayer to retard the formation of brittle Al3Ti intermetallic phase. Mechanisms of microstructural evolution in Al side of the weld have been identified as Dynamic Recovery, Dynamic Recrystallization and particle stimulated nucleation. Significant improvement in the tensile ductility had been observed due to the presence of finer particles. The presence of Nb in the weld nugget influences the microstructural evolution and tensile properties of the weld by reducing the formation of intermetallics.

The welding of aluminum (Al) and titanium (Ti) is difficult and challenging due to the differences in their chemical and physical properties, and the formation of brittle intermetallic phases. In the present experiment, a zinc (Zn) interlayer was used during friction stir welding of Al to Ti. The weld was characterized in detail to understand the mechanisms associated with microstructural evolution and improvement in mechanical properties of the weld. X-ray computed tomography results reveal three-dimensional distribution of particles and flakes of titanium in the weld nugget. It was also observed that Ti particles are inhomogeneously distributed in the weld and the distribution depends on their morphology. Such a distribution of Ti was informative in understanding material flow. In addition, the consolidation of Zn in the Al matrix reveals the nature of material flow in the weld nugget as well. The importance of the Zn interlayer and mechanism of phase formation was explored in this study. It was characterized that the mechanical mixing of Zn with Al and Ti alters phase evolution and restricts the formation of conventional Al3Ti intermetallic phase. The presence of zinc homogenizes elemental distribution and inhibits the formation of brittle intermetallic phases, which leads to a substantial improvement in mechanical properties of the weld.

In this study, deformation behavior of AM30 magnesium alloy is investigated in the hot working regime and empirical relations are developed. Compression tests were performed in the 0.001-10 s−1 strain rate range and 423-623 K temperature range to obtain the mechanical properties. The compression curves were fitted using two approaches, viz. piecewise linear fitting and a Johnson–Cook type relation. Piecewise linear fit is found to be appropriate for describing the mechanical behavior in the dynamic recrystallization (DRX) regime as compared to the proposed Johnson–Cook type relation. The Johnson–Cook type model is not able to capture the essential feature of DRX, particularly at high strain rates.

In this paper, a novel technique to enhance yield strength of twinning induced plasticity (TWIP) steels has been reported by producing a gradient microstructure. Such a microstructure is generated using surface mechanical attrition treatment (SMAT). The SMAT processed steel exhibits a composite microstructure, comprising of hard phase at the surface and soft phase at the core. The deformed microstructure consists of a graded distribution containing of twins, high density of dislocations and nano-crystalline grains. As a combined effect of the three, a significant improvement in the yield strength is observed without much loss of ductility. (C) 2018 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved.

We report here, interrelation between orientation dependent spheroidization 1] and bulk texture evolution during static annealing of warm-rolled Ti-6Al-4V alloy. Weakening of basal fibre (ND parallel to < 0001 >) and complementary strengthening of prism fibre (RD parallel to < 10 (1) over bar0 >) occur on annealing, which is unique and contrary to previous reports. Texture transition is conjugated with two counteracting processes, both being alpha-colony orientation dependent: spheroidization of alpha(P)-phase increasing spread of the fibres, and variant selection during alpha(P) -> beta -> alpha(s) transformation strengthening only the prism fibre. Basal fibre weakens from orientation dependent spheroidization on annealing, while prism fibre intensity is maintained or increased from alpha(s) selection depending on annealing durations. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

During Friction Stir Welding (FSW) of aluminum (Al 2024) to titanium (Ti-6Al-4V), it is observed that titanium fragments at the interface get distributed in the weld nugget. These particles are both coarse and fine in size. Such a particle distribution, particularly due to presence of coarse particles, is expected to negatively impact the mechanical properties of the welds. In an effort to further fragment the coarse Ti particles, FSW was performed with an additional pass in the weld nugget region. Characterization was done using X-ray Micro-Computed Tomography (XCT), Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS), X-ray Diffraction and Electron Back-scattered Diffraction (EBSD) method. Tensile tests were performed to determine the mechanical properties of the weld. The Ti particles of various shapes and sizes were seen to be inhomogeneously distributed in the weld nugget even after the second pass. A detailed observation revealed that the larger particles (as flakes) were inhomogeneously distributed but the finer particles (more spherical) were homogeneously distributed in the weld nugget. It is observed that the weld after second pass contains a higher number of finer Ti particles. The variation in particles size and number fraction is due to the continuous fragmentation that occurs during the processing. Phase analysis reveals the formation of intermetallic compounds such as Al3Ti and AlTi in the welds. A detailed analysis discloses that the fraction of intermetallics in the weld nugget increases in the second pass when compared to the first pass. Aluminum in the weld nugget was substantially refined and recrystallized with grains consisting of mixed types of grain boundaries, which points to the mechanism of Continuous Dynamic Recrystallization (CDRX) through Dynamic Recovery (DRV). The EBSD analysis also reveals that the weld after second pass promotes the development of a high fraction of recrystallized grains (87%) when compared to that of first pass (78%). The second pass resulted in a significant improvement in the ultimate tensile strength (from 231 ± 8 MPa to 271 ± 6 MPa) and ductility (from 7.4 ± 0.3% to 9 ± 1.0%) of the weld. Such improvement in joint properties is analyzed considering the relative mechanical properties of the different zones across the weld nugget. A spring model has been employed to characterize the fracture behavior of the welds. This method and mechanism may be used to produce composite and dissimilar welds with unique mechanical properties by employing multi-pass processing and welding methodology.

In the present work, the influence of strain path on the evolution of microstructure, crystallographic texture, and magnetic properties of a two-phase Fe-Cr-Ni alloy was investigated. The Fe-Cr-Ni alloy had nearly equal proportion of austenite and ferrite and was cold rolled up to a true strain of 1.6 (thickness reduction) using two different strain paths-unidirectional rolling and multi-step cross rolling. The microstructures were characterized by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD), while crystallographic textures were determined using X-ray diffraction. For magnetic characterization, B-H loops and M-H curves were measured and magnetic force microscopy was performed. After unidirectional rolling, ferrite showed the presence of strong alpha-fiber (rolling direction, RD//aOE (c) 110 >) and austenite showed strong brass type texture (consisting of Brass (Bs) ({110}aOE (c) 112 >), Goss ({110}aOE (c) 001 >), and S ({123}aOE (c) 634 >)). After multi-step cross rolling, strong rotated cube ({100}aOE (c) 110 >) was developed in ferrite, while austenite showed ND (normal direction) rotated brass (similar to 10 deg) texture. The strain-induced martensite (SIM) was found to be higher in unidirectionally rolled samples than multi-step cross-rolled samples. The coherently diffracting domain size, micro-strain, coercivity, and core loss also showed a strong correlation with strain and strain path. More strain was partitioned into austenite than ferrite during deformation (unidirectional as well as cross rolling). Further, the strain partitioning (in both austenite and ferrite) was found to be higher in unidirectionally rolled samples.

P.G thanks Department of Science and Technology, Govt. of India (SR/S4/FS-481/2009), Ministry of Earth Sciences (MoES/ATMOS/PP-IX/09), Divecha Centre for Climate Change, Australian Scientifc Instrument and I.W thanks Australian Scientifc Instrument for funding the project.

In the present study, microstructure and texture development during single and multiple pass friction stir processing (FSP) of a strain hardenable wrought Al Mg alloy (AA5086) was investigated. Subtle differences were observed while comparing with heat treatable alloys in the nucleation mechanism of the recrystallized microstructure observed in the nugget zone. Strain induced boundary migration was the dominant mechanism of microstructure evolution in the alloy, which influenced the crystallographic texture development by weakening it. Micro-texture measurements reveal variations in the crystallographic texture along the thickness of the sample. Recrystallization texture components were observed in the nugget zone indicative of a pronounced static recrystallization in the alloy as compared to the heat treatable alloys. Bulk texture measurements within the nugget zone of the optimally processed sample reveal a relatively dominant C component of shear texture. Average grain size in the nugget zone remained the same and the bulk crystallographic texture components were retained during multiple-pass FSP. The lower strain energies involved and the enhanced recovery processes due to the high temperature materials processing of the alloy during FSP resulted in a stable microstructure and texture. In summary, FSP could be promoted as a competent and suitable secondary processing technique for the bulk production of ultra-fine-grained materials in strain hardenable aluminium alloys.

The deformation behavior of pure molybdenum (Mo) was studied in very high temperature range (1400-1700 degrees C) by carrying out uniaxial compression tests at four different strain rates (0.01-10 s(-1)). Three types of stress-strain curves including work hardening, steady state and softening behavior were observed depending upon the deformation condition. The strain rate sensitivity (m) map generated from the flow stress data revealed two domains of high m values - one at about 1400 degrees C and 10(-1) s(-1) and the second one at similar to 1700 degrees C and strain rate of 10(-2)-1 s(-1). The kinetic analysis of the deformation data yielded the apparent activation energy as 390 kJ mol(-1), the stress exponent as 8.5, and the activation volume about 100-600 b(3) for pure Mo. Microstructures of the deformed samples were investigated using the electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM). The appearance of smaller strain-free grains along the boundaries of deformed grains indicated the occurrence of dynamic recrystallization (DRX) in the samples deformed at conditions corresponding to the high m values. Grain growth was significant at higher temperature and lower strain rate deformation. Bulk texture measurements of the hot deformed samples indicated strengthening of < 001 > fiber texture during occurrence of the DRX.

A novel in-situ synthesis technique has previously been proposed for the synthesis of magnesium based nano composites, by exploiting the thermodynamic reactions, to fabricate nanoparticles in-situ during the melt processing. Although the microstructural aspects of formation of such nanocomposites have been dealt with previously, the implications of the same on the texture and hence on mechanical properties are not certain. In the present work, the evolution of crystallographic texture and its influence on tension-compression asymmetry (Tensile yield strength divided by Compressive yield strength) and thereby, the impact on fatigue failure mechanisms is studied by comparing the behaviour of Mg-1.8Y/1.53ZnO nanocomposite and its monolithic alloy, Mg-1.8Y. The Mg-1.8Y/1.53ZnO nanocomposite revealed a very strong two component texture, not akin to the weak texture of Mg-1.8Y alloy. The texture was attributed to the loss of Y in the matrix and consumption of Y in formation of Y2O3 nanoparticles in-situ and the formation of the beta(1)' (Mg-Zn') rods during extrusion. Further, this texture exhibited by the nanocomposite favoured high twinning activity under compression, thereby causing strong asymmetry in the tensile and compressive yield strengths. The fatigue tests indicated a superior performance of the nanocomposite as compared to the alloy. The deformation and damage mechanisms, when studied in correlation with the asymmetry revealed that the asymmetric materials exhibit steeper S-N curves as compared to the symmetric materials.

Magnesium has been trending of late in automobile, aerospace, defense, sports, electronic and biomedical sectors as it offers an advantage in light-weighting. In aluminum, titanium, and steel dominated aerospace and defense sectors, applications of Mg were banned/restricted until recently due to perceived easy ignition and inability to self-extinguish immediately. Strength is generally inversely related to ductility, weak texture and unrelated to ignition resistance, making it challenging to optimize all four concurrently in a material. We address this challenge by designing a low density (~1.76 g.cm−3) in-situ Mg nanocomposite. It is a resultant of a sequence of in-situ reactions during melt processing and extrusion. The in-situ formed Y2O3 nanoparticles exhibit coherency with matrix and lead to development of large amount of elastic and plastic strain fields around them. These nanoparticles and secondary phases (Mg2Ca and Mg2Y) are responsible for the nanocomposite’s high tensile strength (~343 MPa). A weak texture mediated tensile ductility of 30% and compressive failure strain of 44% is observed. Further, the ignition temperature increased to 1045 °C (near the boiling point of Mg) due to the formation of protective surficial oxide layers aided by the presence of insulating Y2O3 nanoparticles, rendering the nanocomposite outperform other traditional commercial Mg-based materials.

The Cretaceous greenhouse climate was accompanied by major changes in Earth’s hydrological cycle, but seasonally resolved hydroclimatic reconstructions for this anomalously warm period are rare. We measured the δ18O and CO2 clumped isotope Δ47 of the seasonal growth bands in carbonate shells of the mollusc Villorita cyprinoides (Black Clam) growing in the Cochin estuary, in southern India. These tandem records accurately reconstruct seasonal changes in sea surface temperature (SST) and seawater δ18O, allowing us to document freshwater discharge into the estuary, and make inferences about rainfall amount. The same analytical approach was applied to well-preserved fossil remains of the Cretaceous (Early Maastrichtian) mollusc Phygraea (Phygraea) vesicularis from the nearby Kallankuruchchi Formation in the Cauvery Basin of southern India. The palaeoenvironmental record shows that, unlike present-day India, where summer rainfall predominates, most rainfall in Cretaceous India occurred in winter. During the Early Maastrichtian, the Indian plate was positioned at ~30°S latitude, where present-day rainfall and storm activity is also concentrated in winter. The good match of the Cretaceous climate and present-day climate at ~30°S suggests that the large-scale atmospheric circulation and seasonal hydroclimate patterns were similar to, although probably more intense than, those at present.

Commercially pure titanium (cp-Ti) is a metallic biomaterial used in orthopedic and cardiovascular applications. Here, surface nanocrystalline cp-Ti produced by surface mechanical attrition treatment (SMAT) is shown to exhibit multifunctional properties for orthopedic and cardiovascular applications. Nanocrystallization simultaneously enhanced the stem cell response and fatigue resistance in simulated body fluid of cp-Ti collectively required for load bearing orthopedic applications. Stem cell attachment and proliferation was enhanced by 20% and number of cycles to failure increased by 15% after nanocrystallization. Nanocrystalline Ti was also found to be suitable for cardiovascular applications due to its improved hemocompatibility. A 40% reduction in attachment of platelets and their activation was noted on the surface of nanocrystalline Ti. While high surface hardness and compressive residual stress improved the corrosion-fatigue resistance, the biological response of stem cells and platelets was governed by the physico-electro-chemical properties of the surface oxide on cp-Ti. Modulation in properties of the oxide layer altered the protein adsorption, evaluated by means of electrochemical impedance spectroscopy and direct protein quantification thereby, augmenting the biological response. Taken together, it is demonstrated that surface nanocrystallization by SMAT is a promising step towards producing high performance Ti implants for orthopedic and cardiovascular applications. Keywords: Surface nanocrystallization, Surface mechanical attrition treatment, Corrosion-fatigue, Stem cells, Hemocompatibility, Protein adsorption, Surface oxide

The figure of merit (zT) of a thermoelectric material can be enhanced by incorporation of nanoinclusions into bulk material. The presence of bismuth telluride (Bi

Effect of change in strain path during rolling and its role in the development of crystallographic texture after deformation and then after recrystallization has been studied for Ni-40wt%Co which is a medium stacking fault energy (SFE) material. Results indicate that textures developed after unidirectional rolling and multi-step cross-rolling are quite different which also leads to different texture evolution after recrystallization. Microstructure of both UDR and cross rolled sample shows band type of feature within the grain having lesser band density for cross rolled samples. After recrystallization unidirectionally rolled sample shows bimodal whereas cross rolled sample shows equiaxed grain size distribution. But all the samples show large fraction of annealing twins. It has been shown that in all cases formation of annealing twins have large influence on the texture transition after recrystallization.