High Resolved Shear Stress Research Articles

Effects of σ phase embrittlement and Al addition on the ductile-brittle transition in super ferritic stainless steels

The precipitation evolution and mechanical behaviour of Al-modified and Al-free super ferritic stainless steels (SFSSs) subjected to hot-rolling and isothermal aging at 850 °C were investigated comparatively. Experimental results revealed that hot-rolled samples devoid of Al exhibited elongated fibre microstructure including many sub-grain boundaries and shear bands, whereas a surface recrystallization layer was observed in Al-modified samples. During isothermal aging, σ, χ, and Laves phases were observed in Al-free samples, whereas primarily Laves phases and a small σ phase were identified in 1.0 wt%Al samples. Rolling deformation accelerated the σ phase precipitation kinetic, whereas the addition of Al inhibited σ phase precipitation and promoted Laves-phase precipitation. The bulky σ phase precipitation caused the cleavage fracture in SFSSs owing to the high critical resolved shear stress for dislocation glide on {110}<001>, {100}<001>, {100}<010>, and {111}<0-11> slip systems and the easy crack initiation and propagation in the σ phase during tensile test. Despite being aged for 16 h, Al-modified SFSSs exhibited a significant elongation of 22.6 %. This study highlights that Al addition would facilitate not only the low-temperature hot rolling of SFSSs but also SFSS production without the need for solution treatment prior to cold rolling, thereby offering a promising short-process approach for industrial manufacturing.

Optimizing toughness in high entropy alloys using a genetic algorithm: A combined computational and experimental approach

A genetic algorithm (GA) was developed to search for high entropy alloys (HEAs) with good combinations of mechanical properties. The algorithm was designed find single-phase face-centered cubic (FCC) HEAs, already known for their ductility, with high Hall-Petch constants (K) and high critical resolved shear stresses (τY). The objective was to develop a methodology that allows the design of HEAs in a multi-objective environment, focusing on alloys that exhibit enhanced ductility and strength, achieved through an increase in its yield point without significant loss of its ultimate deformation via adjustments of K and τY values, resulting in an alloy with high toughness. The most promising alloy suggested by the genetic algorithm was an unconventional composition (Co32.73Cu15.11Fe0.72Hf0.72Mn35.97Mo3.96Ni10.43Sn0.36), with eight different elements in non-equiatomic ratios with maximized K and τY values. This alloy was then experimentally produced and characterized by scanning electron microscopy (SEM), synchrotron x-ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness, with the objective of validating the predictions made by the GA. An advantage of the proposed method is the possibility of more systematically identifying and exploring new compositions in the complex composition space characteristic of these multicomponent alloys, as it directs its search towards domains that can be used to solve challenging problems involving multi-objective optimization. However, the thermodynamic parameters used for single-phase FCC prediction, namely the valence electron concentration (VEC) and the dimensionless thermodynamic parameter φ, exhibited limitations. These limitations were further explored in the present study, as evidenced by the fact that the microstructure of the selected alloy was not single-phase, which hindered the study of the mechanical properties, predicted exclusively for monophasic FCC alloys. Therefore, this work highlights the necessity for the development of novel thermodynamic equations for phase prediction, or even the integration of the genetic algorithm with other methodologies, such as CALPHAD calculations, to achieve enhanced results.

Experimental and digital twinning in ZnAlMg coatings

Twinning is a major deformation mechanism in various materials, especially when few dislocation slip systems are operative. It is the case of zinc-rich coatings in galvanised steel sheets, made of pancake grains on a substrate and where the slip systems with a non-vanishing component along the c-axis present high critical resolved shear stress values. In addition, the abrupt lattice orientation change associated to twinning, the stress relaxation during its propagation and the localised nature of its early stages make it difficult to reproduce this deformation mechanism by using classical crystal plasticity models conceived for dislocation slip. In this sense, this work proposes a hierarchy of three twinning models in combination with a dislocation slip crystal plasticity model, for the case of a ZnAlMg coating. These three models are: a relaxed-Taylor model applied to individual crystal orientations of the coating, a “pseudo-slip” model for twinning and a localised twinning model. The latter incorporates a linear softening in the material law accounting for the unstable twinning initiation and enforces twinning lattice reorientation. A microstructure portion extracted from an in-situ SEM tensile experiment on galvanised steel is used to perform 3D full-field finite element simulations within a finite strain formulation. SEM observations and EBSD acquisitions are used to compare simulation and experimental results during the different steps of the in-situ SEM test, regarding the deformation and damage modes of the zinc-rich coating. The focus is set on twinning evolution inside some individual grains, and the pros and the cons of the three models are finally discussed.

High temperature deformation behaviour and recrystallization mechanism of TiC/Ti6Al4V gradient material fabricated by laser directed energy deposition

Metal-ceramic gradient materials are of considerable interest due to their unique capability to integrate the ductility of metals with the mechanical strength and high-temperature resistance of ceramics, thereby reducing the risk of cracking induced by thermal stress. In this article, TiC/Ti6Al4V gradient materials were prepared through the laser directed energy deposition (LDED) process. Subsequently, high-temperature compression tests were performed at various temperatures to investigate the deformation behaviour and recrystallization mechanism of the gradient materials. The Zener-Holomon constitutive equation was then used to calculate the gradient material at 750–900 °C and 0.001–0.1 s−1 to obtain a deformation activation energy of 362.36 KJ·mol−1. The EBSD was used to analyze the microstructural evolution of the gradient material. The results indicate a significant reduction in the average grain size of the specimens after high-temperature compression, and a more random crystal orientation due to the occurrence of dynamic recrystallisation (DRX). The primary softening mechanism of TiC/Ti6Al4V gradient materials is discontinuous dynamic recrystallisation, with TiC primarily affecting the nucleation of discontinuous dynamic recrystallisation (DDRX) and the subsequent grain growth. The nucleation becomes easier with increasing TiC content. However, the TiC hinders the migration of grain boundaries, resulting in a smaller DDRX grain size. After high-temperature compression, the main slip system of the crystal is converted from Pri to Bas. Pyr is difficult to activate due to its high critical resolved shear stress.

The mechanical anisotropy of Mg-Zn-Y alloys with columnar crystals in specific orientation

The Mg99.2Zn0.2Y0.6 alloys were prepared by directional solidification, and the effect of loading modes on mechanical anisotropy and deformation mechanism of the alloys was studied. The microstructure of the alloy is columnar crystals whose growth orientations are mainly concentrated in <112(_)0>. When the tensile load is parallel to longitudinal grain boundaries of columnar crystals, the alloy has high yield strength (232 MPa), owing to basal <a> slip with hard orientation and {101(_)1} contraction twinning with high critical resolved shear stress (CRSS), but work hardening is not obvious. When the compressive load is parallel to longitudinal grain boundaries of columnar crystals, the alloy has high compressive strength (337 MPa) and good plasticity (maximum strain, 24 %), as well as distinct work hardening, which are related to (112(_)1) [112(_)6(_)] twins and good strain compatibility of grain boundaries. When the compressive load is perpendicular to longitudinal grain boundaries, the alloy shows high plasticity (maximum strain, 31 %) because the strip-like extension twins are parallel to the longitudinal grain boundaries during deformation.

The Effect of Rolling Reduction on the Microstructure Evolution and Slip Behavior of Ta-10W Alloy during Cold Rolling Process

In this study, we investigated the influence of cold rolling reduction on microstructural evolution and slip behavior in Ta-10W alloy fabricated by vacuum arc melting (VAM). As the reduction increased, both single and multiple slips were observed within some grain interiors. At reductions of 20% and 40%, deformation bands, primarily consisting of γ-fiber components, formed within the grain interiors. The fraction of deformation bands (DBs) increased with higher reduction. Conversely, at 60% reduction, in addition to DBs, experimentally observed shear bands (SBs) with a herringbone pattern were formed. Both DBs and SBs predominantly formed in regions of concentrated strain (areas with high kernel average misorientation (KAM) and geometrically necessary dislocations (GND)). As the reduction increased, the misorientation angle between the matrix and the DBs or SBs gradually increased, while the width of the DBs decreased. To investigate the violation of Schmid’s law in Ta-10W alloy, slip trace and resolved shear stress (RSS) analyses were performed on observed slip lines within deformed grains. Contrary to conventional slips, where slip typically occurs on the plane with the highest RSS, slips in the Ta-10W alloy were confirmed to occur even on planes with lower RSS in certain grains. Hence, this study provides experimental evidence of Schmid’s law violation in Ta-10W alloy.

Study on anisotropic mechanical behavior of AZ31 magnesium alloys under free-end torsion

In this study, the mechanical behavior and microstructure of a hot-rolled AZ31 magnesium alloy sheet under free-end torsion with torsional axis along rolling direction (RD), normal direction (ND) and 45° in ND-RD plane, have been investigated both experimentally and numerically. The mechanical behavior under torsion, including stress-strain response, Swift effect and strain hardening rate, present obvious anisotropy. The Swift effect is sensitive to the direction of torsion axis and exhibits remarkable anisotropy with axial elongation in ND sample and axial shortening in RD and 45° samples. The axial elongation or shortening is determined by both slips and extension twin, with extension twin exerting a greater influence on the extent of the axial deformation. During shear straining, the dominant deformation mode transforms basal slip to prismatic slip with the axial direction deviating from ND to RD, while the second-order pyramidal ⟨c+a⟩ slip is nearly not activated during whole deformation attributed to its high critical resolved shear stress. Based on the effective Schmid factor (ESF) of deformation modes, the grains with favored orientation would get activation of {101‾2} extension twin due to the high ESF, resulting in the different twin volume fractions. Additionally, the activation of twin relative to basal slip has a connection with the increasing trend of normalized strain hardening rate.

Fractography of Stress Corrosion Cracking of 20% Cold Worked Type 304 H Stainless Steel Containing δ-Ferrite in Oxidizing Primary Water

Fractography of stress corrosion cracking (SCC) of 20% cold worked Type 304 H stainless steel containing δ-ferrite was studied using a compact tension (CT) specimen in oxidizing primary water with a scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). The stress corrosion crack propagated mostly in transgranular stress corrosion cracking (TGSCC) mode and sometimes in intergranular stress corrosion cracking (IGSCC) mode. TGSCC paths were along the {111} plane with both high resolved shear stress and high resolved tensile stress. IGSCC preferentially propagated along the grain boundary perpendicular to the loading axis. The findings in this work suggest that TGSCC proceeds through formation of a weakening zone at the head of the crack tip by interaction of slip and corrosion and then cracking of the weakened zone by tensile stress.

Evolution of Microstructure and Crystallographic Texture in Deformed and Annealed BCC Metals and Alloys: A Review

Dislocation slips, twinning, shear banding (SBs), strain localization, and martensite formation are a few deformation modes that are activated in BCC metals and alloys. Strain, strain rate, and deformation temperature are other parameters that determine the activation of deformation modes in BCC alloys. This review focuses on several BCC alloys, such as beta-titanium (β-Ti), tantalum (Ta), and ferritic stainless steels (FSSs), all of which exhibit differences in deformation behavior. These alloys often undergo thermo-mechanical processing (TMP) to enhance their mechanical properties. TMP leads to the evolution of deformation-induced products, such as SBs, strain-induced martensite (SIM), strain localizations, and mechanical/deformation twins (DTs) during plastic deformation, while also influencing crystallographic texture. The deformation modes in β-Ti depend upon the stability of the β-phase (i.e., β-stabilizers); low-stability alloys show the formation of SIM along with slips and twins, whereas in highly stable β-Ti alloys, only slip+twin modes are observed as the primary deformation mechanisms. In the case of Ta, slip activity predominantly occurs on {110} planes, but it can also occur on planes with the highest resolved shear stress. The breakdown of Schmid’s law or non-Schmid behavior for Ta and Ta-W alloys has been discussed in detail. The cold rolling (CR) of FSSs results in the formation of ridges, which is an undesirable phenomenon leading to very low formability. The microstructures of the rolled sheets consist of elongated ferrite grains with in-grain SBs, which are preferentially formed in the γ-fiber-oriented grains. The formation of finer grains after recrystallization improves both the mechanical properties and ridging resistance in FSS. Therefore, this review comprehensively reports on the impact of TMP on the microstructural and crystallographic texture evolution during the plastic deformation and annealing treatment of β-Ti, Ta alloys, and FSSs in BCC materials, using results obtained from electron microscopy and X-ray diffraction.

A unified non-empirical strength model

Strength, as an important indicator of structural materials, has always been an important research topic in materials science. Theoretically, building a strength model is a rewarding method to understand the relationship between the mechanical properties and microstructure of materials. Although many strength models can reduplicate experimental values very well, they are empirical models, and their applicability is limited to materials for which empirical parameters have been obtained. Here, a non-empirical strength model is proposed based on the two-dimensional (2D) displacement potential of dislocation slipping, which can be applied to different chemically bonded crystals. Owing to the large electron localization function (ELF), covalent and ionic crystals have a high 2D displacement potential of dislocation slipping, and their dislocation slip mode prefers the kink-pair mode, further exhibiting a high critical resolved shear stress (CRSS). In contrast, metallic crystals with a small ELF have a low 2D displacement potential of dislocation slipping, and their dislocation slip mode is more inclined to the string mode, showing a low CRSS. This work provides new insights into dislocation-slipping configurations that will be useful for the development of new high-performance structural materials.

Characterization of Lomer junctions based on the Lomer arm length distribution in dislocation networks

During the plastic deformation of crystalline materials, 3d dislocation networks form based on dislocation junctions. Particularly, immobile Lomer junctions are essential for the stability of dislocation networks. However, the formed Lomer junctions can unzip and dissolve again, if the linked mobile dislocations of the Lomer junction - the Lomer arms - experience sufficiently high resolved shear stresses. To generate a better understanding of the dislocation network stability and to pave the way to a general stability criterion of dislocation networks, we investigate the Lomer arm length distribution in dislocation networks by analyzing discrete dislocation dynamics simulation data of tensile-tested aluminum single crystals. We show that an exponential distribution fits best to the Lomer arm length distribution in the systems considered, which is independent of the crystal orientation. The influence of the slip system activity on the Lomer arm length distribution is discussed.

Simultaneous enhancement of strength and ductility for AZ31 magnesium alloy by pre-twinning induced heterostructure

Pre-twinning was used to tailor the strength and ductility of AZ31 magnesium alloy. Simultaneous enhancements in both ductility and strength were achieved in the AZ31 after the introducing of a high fraction of twin-matrix pairs. The slip trace analysis indicated that although the area-weighted average global Schmid factors (SFs) were not significantly changed, much more non-basal slip was activated in the pre-twinned sample compared with that in the as-received sample, which was beneficial to achieving higher work hardening and obtaining higher uniform elongation. The high-resolution digital image correlation (DIC) combined with ex-situ electron backscatter diffraction (EBSD) characterization revealed that the uniformity of the grain-size scale strain distribution was improved and the local strain concentration at the boundary was reduced during the loading as result of the extra activated non-basal slip, which delayed intergranular crack initiation and increased ductility. The activation of much non-basal slip with high critical resolved shear stress, the hetero-deformation, and the fine equivalent grain size caused the strengthening of the AZ31 sample with a high fraction of twin-matrix pair interfaces. These results imply that tailoring the twin-matrix interface density is an effective strategy to achieve excellent strength-ductility combinations in HCP metals.

Effects of temperature and loading direction on deformation mechanism of Ti-10at%Al alloy subjected to rolling and high speed compression

In this paper, Ti-10at%Al alloy samples were subjected to rolling and high speed compression under different temperatures and along different loading directions (the transverse direction (TD) and normal direction (ND) of the pre-rolled samples), to explore the effects of temperature and loading direction on the deformation mechanisms.101̅2 and 112̅1 twins were activated in all these deformed specimens. 112̅1 twins prevailed in both the room temperature rolled and liquid nitrogen rolled specimens but were severely inhibited during hot rolling, while 101̅2 twins did not show obvious change with the temperature. Planar slip of dislocations occurred during room temperature rolling and liquid nitrogen rolling, while cross slip occurred during hot rolling. The change of dislocation behaviors at different temperatures may be caused by the variation in stacking fault energy as an effect of temperature. Moreover, the number of twins in the deformed samples along TD was always higher than that along ND both under rolling and high speed compression. When loaded along TD, most of the grains were with or close to the orientations of<21̅1̅0> and<101̅0> , which were favorable for the activation of 101̅2 and 112̅1 twins. Therefore twinning played a significant role when loaded along TD, while dislocation slip dominated the deformation when loaded along ND. The hardness increased after deformation under different conditions, and the hardness of specimens after rolling or compression along ND was generally higher than that along TD due to the reason that most of the grains were in the hard< 0001 > orientation when loaded along ND, activation of<c+a> dislocations on pyramidal planes with high critical resolved shear stress was required.

Crystal plasticity phase-field simulation of slip system anisotropy during creep of Co-Al-V monocrystal alloy under multidirectional strain

The preferable thermodynamic stability of L12 γ'-Co3(Al, V) phase and wide γ+γ' two-phase region endow the Co-Al-V alloy with great application potential. By introducing the digitized image of SEM morphology into phase-field simulation, utilizing the sublattice free energy model and the crystal plasticity strain model to simulate the anisotropic slip system, the rafting behaviors of the L12 γ'-Co3(Al, V) phase and the creep properties of Co-5Al-14V (at.%) alloy under tensile, compressive, shear, and monoclinic strains are studied. The partitioning ratio of element and orientation degree of γ' phase indicate that the uniaxial compressive strain improves the microstructural stability and the creep resistance at early creep stage. The creep resistance of alloy in state of equilibrium volume fraction of γ' phase is superior to that in the nonequilibrium volume fraction, and the creep resistance increases in order of tensile strain, compressive strain, and shear strain. Additionally, the dominant octahedral slip systems in fcc structure are (1¯1¯1)[101] under tensile strain, (1¯11)[01¯1] under compressive and 15° monoclinic strains, and (1¯1¯1)[1¯10] under 45° monoclinic strain. The hardening effect is prominent in γ matrix, and the high average critical resolved shear stress leads to the low creep strain. This study reveals the correlations between the slip system anisotropy and creep behaviors of Co-Al-V alloy under external strain, and also provides a method to combine the phase-field simulation with the experimental image for predicting the morphology evolution.

Dislocation-dominated void nucleation in shock-spalled single crystal copper: Mechanism and anisotropy

Large-scale molecular dynamics simulations are conducted on single crystal copper along eight representative orientations to investigate dislocation-dominated void nucleation during shock loading and spall failure, including mechanisms and anisotropy. Spall strength estimated from free surface velocity decreases in the order of group I ([001]), group IV ([012] and [011]), group III ([122] and [123]) and group II ([114], [112] and [111]), respectively, in good agreement with anisotropy of spall strength in previous experiments and simulations. A lower spall strength is statistically associated with a higher void nucleation rate and a higher density of stable immobile dislocations (1/6〈110〉 and 1/3〈100〉) formed before void nucleation. Stable immobile dislocation plays a key role in void nucleation. The formation of stable immobile dislocations requires three conditions: high resolved shear stress for activating mobile dislocations, two or more main slip planes for dislocation reaction, and high angle between activated slip directions for high stability of immobile dislocations. Based on crystal elastic–plastic theory, resolved shear stress on all slip systems is calculated to analyze orientation effects on the three conditions. The three conditions can be fulfilled by group II orientations, but cannot by group I, III, and IV orientations, leading to anisotropy in void nucleation and spall strength.

Deformation mechanism of ferrite in a low carbon Al-killed steel: Slip behavior, grain boundary evolution and GND development

The forming quality and performance of double walled brazed tube formed by steel sheet are seriously affected by the deformation behavior of the initial sheet. In this work, the deformation mechanism of ferrite in a low carbon Al-killed steel sheet was investigated by in situ tensile and electron backscatter diffraction (EBSD) tests. It is found that ferrite presents single slip, double slip and cross slip as well as slip transfer behavior in the deformation process. The activation of the {110}<111> slip system is the main deformation mode, the less activation number of {112}<111> and {123}<111> is due to the orientation dependence and high critical resolved shear stresses (CRSS), respectively. A high Schmid factor (SF) or geometric compatibility factor m' will contribute to slip transfer. Meanwhile, the evolution of low angle grain boundaries (LAGBs) is the main deformation feature for ferrite polycrystals, and the fraction of 2–5° LAGBs in the whole LAGBs shows a strong linear relationship with strain. The subdivision of grains and rotation of different parts lead to the gradual evolution of LAGBs into high angle grain boundaries (HAGBs). Furthermore, small grains are more likely to accumulate the geometrically necessary dislocation (GND) because the microstructural unit size restricts the movement of dislocation, while the less effect of grain orientation is related to the high SF for all grains.

The activation of compression twin pairs and plasticity improvement of directionally solidified Mg alloy

The <112¯0> orientated Mg-4.70Zn-0.38Y-0.14Zr alloy with high product of strength and elongation (PSE = 5346 MPa•%) was prepared using directional solidification technology. Electron Back Scatter Diffraction (EBSD) and High Resolution Transmission Electron Microscopy (HRTEM) were applied to explore the deformation mechanism and plasticity improvement of experimental alloys. Experiment results showed that the dominant deformation systems were non-basal slipping systems and compression twin pairs (CTPs). High critical resolved shear stress (CRSS) of non-basal slipping system increased the yield strength (180 MPa) and tensile strength (198 MPa). The CTP followed the geometrical relationship of TP1 (twinning plane of variant1)∥TP2 (twinning plane of variant2) and appeared in a wider misorientation range than tensile twin pair which was classified as twinning shear transmission and had high geometric coordination factor (m’). Calculation results showed that the stress concentration at the junction of CTP and grain boundaries was the same as inside the compression twin. 60% of x/<11 2¯ 0> (0°≤x < 180°) grain boundaries in experimental alloy satisfied this geometrical relationship, leading to the general activation of CTP and plasticity improvement (elongation is 27%).

Slip activity during low-stress cold creep deformation in a near-α titanium alloy

Near-α titanium alloys are known to be susceptible to cold dwell fatigue (CDF) debit, which has been linked to the occurrence of cold creep during high-load dwell times superimposed onto low cycle fatigue loading. In order to shed new light on the deformation mechanisms during cold dwell and to understand better the role of the microstructure, two different bimodal microstructures (fine and coarse transformation product) of TIMETAL®834 were investigated at stress levels below the 0.2% proof stress using a combination of grain orientation mapping and in-situ electron microscopy imaging. This enabled in-depth analysis of 2D slip patterns and slip system activity using High-Resolution Digital Image Correlation (HRDIC), showing that in both microstructures basal slip is initially the dominant slip mode before prismatic slip activity increases approaching the 0.2% proof stress. Comparing the two constituents in the bimodal microstructure, first slip bands are localised predominantly in primary α grains, indicating higher strength of secondary α colonies, particularly for finer transformation products. During 10 min load holds at stresses below 0.2% proof stress, more plastic strain and longer connected slip traces across several grains were observed in the sample with coarse transformation product, indicating higher susceptibility to cold creep deformation.Full-field crystal deformation modelling was used to determine local stresses in individual grains at the onset of plasticity and test the hypothesis that the dominance of basal slip at low-stress levels can be explained by the elastic anisotropy in Ti alloys. While consideration of elastic anisotropy increased resolved shear stress (RSS) values for basal slip relative to prismatic slip, it did not unambiguously explain the early activation of basal slip. Furthermore, thermal residual stresses at the crystal level, due to the anisotropy of coefficients of thermal expansion (CTE), were included in the simulation, which created a wider spread of the RSS data but did not preferentially promote high RSS values for grains well aligned for basal slip. In the absence of an unambiguous conclusion, it is hypothesised that basal slip might display lower critical resolved shear stress values than typically reported but high work hardening rates compared to prismatic slip.

Revealing the effect of local stresses on twin growth mechanisms in titanium using synchrotron X-ray diffraction

Deformation twinning has a significant impact on the evolution of microstructure and mechanical response in hexagonal close packed (hcp) metals. Understanding the physical mechanisms associated with twin nucleation and growth processes is important to enable the broad use of hcp metals. While both nucleation and growth are conditioned by the local stress state, few studies have quantified it in bulk deformed samples. In this study, we reveal the effects of local stresses on twin thickening using in-situ synchrotron experiments with differential aperture X-ray microscopy. High purity Ti is deformed under four-point bending to activate {1012} tensile twins. 3D stress fields with a spatial resolution of 0.5μm are mapped in the vicinity of low and high macroscopic Schmid factor (MSF) twins growing inside a grain. Reconciling this experimental analysis with recent twin growth models reveals that the growth of low MSF twins is limited by the nucleation of twin growth defects in the high-purity Ti sample. While growth-inducing defect nucleation may occur in many places on the interface of the high resolved shear stress (RSS)/MSF twin, the nucleation rate of twinning disconnections for the low MSF twin is high only at the end of the twin near a stress concentration. Once nucleated, these defects easily propagate into lower RSS regions of the grain resulting in twin growth. This work highlights the importance of stress concentrations not only for twin (embryo) nucleation, but also to the growth process of twins, particularly in low MSF twins.

Machine Learning Accelerated, High Throughput, Multi‐Objective Optimization of Multiprincipal Element Alloys (Small 42/2021)

Multiprincipal Element Alloys In article number 2102972, Teng Li and co-workers present a highly efficient design strategy of multiprincipal element alloys (MPEAs) through a coherent integration of molecular dynamic simulation, machine learning algorithms and genetic algorithm. Such a design strategy not only yields remarkable precision of prediction of the critical resolved shear stress and Young's modulus of CoNiCrFeMn MPEAs with an impressively low error, but also enables a drastic 12 600-fold reduction of prediction time in comparison with pure atomic simulations. The multi-objective genetic algorithm further helps identify 100 optimal MPEA compositions with both high critical resolved shear stress and high stiffness.