Resolved Shear Stress Research Articles

Micro-mechanical behavior of lamellar structured Ti6Al4V alloy upon compression via experimental and crystal plasticity study

The micro-mechanical behavior of lamellar structured Ti6Al4V alloy to a small compressional strain of 4.5% was studied. Strain and stress intends to localize along grain boundaries (GBs), triple points (TPs) as well as grain interiors (GIs). The maximum strain and stress is found at some GB-TPs with soft and grain clustering mostly owing to their strong strain incompatibility. Their heterogeneous distribution is highly related to individual crystallographic orientation, their size, shape and grain-grain interactions. The local dislocation behavior forms ledges along with Geometrically necessary dislocations (GNDs) to accomodate strain incompatibility. EBSD and crystal plasticity (CP) simulation disclosed some long range meso-bands (about 45° to loading direction) which crosse multi-grains and some mini-bands within grain interiors (GIs) reflecting a concentrated strain behavior and ductile nature of the Ti6Al4V material. Prismatic slip dominates Ti6Al4V lattice (mainly from surface dislocation activation) determined by its low critical resolved shear stress (CRSS) which is away from some findings of literature. Dislocation is found commenced from some high angle GBs (HAGBs) and extened into GI which can pass through GBs of both low (LA) and high angles given their slip plane coherency. The substructures (α-lamellae) separated by LAGBs within α-colonies, have no significant effect to dislocation movement. Fatigue failure can be inferred from the early stage micro-mechanical behavior through accumulated plastic strain and strong strain incompatability. Fractography reaveals fatigue failure from surface, sub-surface, shearing, cleavage and intergranular modes are presumed highly related to surface defects, compressional residual stress gradient, easy prismatic slip and soft and hard GBs. Multiple crack origins from such combinations are deemed for reduced fatigue life of shot peened samples regardless of the surface compressional residual stress being generated.

Orientation selected micro-pillar compression behavior of heavy-ions irradiated RAFMs

The present study aimed to investigate the mechanical property of heavy ions irradiated Reduced Activation Ferrite/Martensitic (RAFM) steels. The CLF-1 steel was irradiated by 33.5 MeV Fe ions at room temperature, resulting a peak displacement damage of 20 displacements per atom (dpa). Experimental analysis was conducted using Electron Backscatter Diffraction (EBSD) mapping-assisted Focused Ion Beam (FIB) technique to prepare micro-pillars oriented along crystal directions <0 0 1>. Subsequently, these fabricated micro-pillars underwent compression tests utilizing a flat indenter within the Nano-indentation setup. Engineering Stress-strain curves were generated for specimens both un-irradiated and irradiated. The yield strength of the un-irradiated and irradiated specimens in the <0 0 1> directions was determined by using the engineering stress-strain curves. In addition, the critical resolved shear stress (CRSS) of the un-irradiated and irradiated specimens was calculated. Microstructural analysis revealed that the formation of dense and fine dislocation loops were appeared in the material after irradiation. By combining the results of microstructure analysis with the dispersion barrier hardening model, the changes in CRSS caused by irradiation were calculated. Furthermore, the number of dislocation lines participating in deformation at a strain of 20 % was quantified, with the irradiated specimen exhibiting an increase of 33 % in comparison to the un-irradiated specimen.

Atomistic Simulations of Dislocation-Void Interactions in Concentrated Solid Solution Alloys

This paper investigates the interaction of edge dislocations with voids in concentrated solid solution alloys (CSAs) using atomistic simulations. The simulation setup consists of edge dislocations with different periodicity lengths and a periodic array of voids as obstacles to dislocation motion. The critical resolved shear stress (CRSS) for dislocation motion is determined by static simulations bracketing the applied shear stress. The results show that shorter dislocation lengths and the presence of voids increase the CRSS for dislocation motion. The dislocation–void interaction is found to follow an Orowan-like mechanism, where partial dislocation arms mutually annihilate each other to overcome the void. Solute strengthening produces a ‘friction stress’ that adds to the Orowan stress. At variance with classical theories of solute pinning, this stress must be considered a function of the dislocation line length, in line with the idea that geometrical constraints synergetically enhance the pinning action of solutes. Modifying the equation by Bacon, Kocks and Scattergood for void strengthening to account for the solute hardening in CSAs allows one to quantitatively predict the CRSS in the presence of voids and its dependency on void spacing. The predictions show good agreement with the simulation data without invoking any fit parameters.

The mechanism for Li-addition induced homogeneous deformation in Mg-4.5wt.% Li alloy

The mechanism by which Li additions induce a more homogeneous deformation was systematically investigated in this study by comparing the deformation behavior of pure Mg and Mg-4.5 wt.% Li using experiments, crystal plasticity simulations, and theoretical calculations. The results of the digital image correlation measurements showed that under tension along the transverse direction (TD), strong localized deformation bands with an angle of approximately 20° with respect to the TD were observed in pure Mg, but were absent in Mg-4.5 wt.% Li. Slip trace analyses indicated that basal slip was the predominant deformation mode for pure Mg, whereas that for Mg-4.5 wt.% Li was prismatic slip. A high relative activity of pyramidal 〈c+a〉 slip, approximately 17 %, was observed in Mg-4.5 wt.% Li at a high strain of 10 %. Contraction or double twins were hardly detected during the entire tension process. Crystal plasticity simulations revealed that the 4.5 wt.% Li addition dramatically reduced the critical resolved shear stress (CRSS) ratio of pyramidal 〈c+a〉 slip: prismatic slip: basal slip, which was 31.5:21:1 for pure Mg and 4.3:1.3:1 for Mg-4.5 wt.% Li. Theoretical calculations using the CRSS ratios determined by simulations revealed that easy and uniform deformation propagation induced by a dramatically reduced CRSS ratio of prismatic slip to basal slip played a more important role in improving the deformation homogeneity, in addition to the enhanced activity of pyramidal 〈c+a〉 slip. The mechanisms for how Li additions improve the ductility of Mg are also revisited in this paper.

Mechanism in scratching of calcium fluoride with magneto-plasticity

Magnetic field-tuned dislocation plasticity (i.e., magneto-plasticity) has attracted growing attention for assistance to limit the damage evolution of brittle ceramics in the material removal process. However, the mechanism controlling material removal of brittle ceramics with magneto-plasticity remains far from clear. Therefore, combined stress field modeling and molecular dynamics (MD) simulations were performed for scratching of a ceramic material, calcium fluoride (CaF2), to investigate the magneto-plasticity mechanism during the material removal process of brittle ceramics. The stress field calculation with magneto-plasticity was first conducted, which suggests a general reduction in scratching stress on the subsurface under the magnetic field effect. It is also found that the degree of reduction in scratching stress is significantly influenced by the magnetic field intensity and direction as well as strain rate. The reduced scratching stress is responsible for the suppressed formation and evolution of cracks and defects in scratching. Subsequently, MD simulations in scratching of CaF2 show that the application of a magnetic field can facilitate dislocation nucleation, enlarge the range of dislocation propagation, and regularize the dislocation distribution, indicating the advancement in elastic-plastic transition and dislocation mobility. From the views of energy criterion and crystal plasticity, a magnetic field can decrease the required work and resolved shear stress for dislocation slip, which results in a lower scratching stress level. The combined theoretical method of this study broadens the comprehension of magneto-plasticity on deformation mechanism in the material removal process of ceramics and offers theoretical direction for the application of magnetic field assistance in ceramic processing.

Deformation behavior and bending strength of single crystal 8 mol% yttria-stabilized zirconia at microscopic scale

Yield phenomena and bending strength of single crystal 8YSZ were evaluated using microcantilever beam specimens with various crystal orientations. Nonlinearity due to plastic deformation was observed in the stress-strain curves, and the yield stress was found to depend on the crystal orientation. TEM observation revealed many areas of disordered lattice in the region where the maximum tensile stress occurred. Resolved shear stress (RSS) was analyzed for the primary {001}<110> and the secondary {110} <11̅0> and {111} <11̅0> slip systems as a function of the angle between the specimen’s longitudinal direction and the [001] orientation, indicating that the RSS for the secondary ones was the critical RSS in the angle at 10° or lower while that for the primary one did so at 20° or higher. The measured bending strength, which depended on the crystal orientation, was lower than, but on the same order of magnitude as, the ideal strength.

Crystal plasticity model of BCC metals from large-scale MD simulations

Accurate crystal plasticity models that faithfully capture the behavior of single crystals under a wide range of loading conditions, such as loading direction, strain rate, and temperature, are still lacking. Here we introduce a novel approach in which a crystal plasticity (CP) model is informed directly from and calibrated to large-scale quantum-accurate MD simulations in which single crystal BCC Ta serves as a testbed material. By analyzing our large set of MD simulations several key insights are obtained leading us to modify constitutive assumptions in order to address deficiencies of existing CP models. Importantly, we observe that the standard notion of fixed slip systems – pairs of slip directions and slip planes – is inadequate for describing high-rate plasticity in BCC tantalum at room temperature. Instead, pencil glide defined as dislocation motion in the maximum resolved shear stress planes (MRSSP) of each Burgers vector is fully consistent with our MD simulation data while providing significant simplifications of the constitutive relations. Our resulting new CP model closely matches the behavior of single crystals observed in high-rate MD simulations while being fully consistent with lower rate experimental results.

Analytical model for estimating calcium solution strengthening in single-crystal Mg-Ca alloys at finite temperatures

Mg is the lightest structural metal and a suitable replacement for heavy steel and Al alloys. However, Mg exhibits poor plastic formability at room temperature, and the strength of conventional Mg alloys is less than that of most Al alloys. Its low formability at room temperature is attributed to the lack of slip systems because of the extremely large gap in the critical resolved shear stress (CRSS) between the lowest basal system and the other slip and twin systems. This low CRSS of the basal slip usually limits the strength of Mg alloys. Therefore, strengthening the basal slip is important to improve the strength and deformability of Mg alloys and enhance their ductility. In this study, we construct an analytical model for predicting the CRSS in single-crystal Mg–Ca alloys at finite temperatures by quantitatively investigating the CRSS for the 〈a〉 dislocation gliding on the basal plane at temperatures from 1 to 500 K through molecular-dynamics computations. The prediction results agree well with our simulation results and the micropillar compression test results of Mg–0.3at.%Ca and Mg–0.6at.%Ca alloys at room temperature.

Prediction of slip activity of crystal grains around semi-circular and semi-elliptical notches in thin-sheet specimens of pure titanium using formulated macroscopic stress distribution and crystal orientation

Thin metal sheets and wires are important materials for various devices used in electrical, mechanical, and medical fields. With the downsizing of these devices, demand for thinner sheets and wires has increased. Amongst the many metals available, pure titanium has been attracting much attention for use in medical and dental devices because of its good biocompatibility in addition to its light weight and high corrosion resistance. However, thin metal sheets and wires are usually polycrystalline materials and, with the downsizing of materials, there is a loss of homogeneity during deformations. Inhomogeneous deformation becomes significant in thin sheets and wires, owing to the different crystal orientations and geometries of crystal grains. Furthermore, the shapes of such devices are not uniform, unlike, say, a simple rod. Therefore, macroscopic stress and strain concentrations should be taken into consideration when designing these devices as they affect the localization of deformation and the resultant fracture. In this study, semi-circular and semi-elliptical notched specimens made of thin-sheet polycrystalline pure titanium are subjected to tensile testing. Inhomogeneous deformation caused by crystallographic slip is observed near the notch root. Analysis of the crystal orientation and observation of the slip line show that the slip initiation in crystal grains is affected by the macroscopic stress distribution and can be predicted from the slip activity calculated from both the critical resolved shear stress on the slip systems and the resolved shear stress acting on prospective slip planes obtained from the macroscopic multiaxial stress distribution.

Effect of variation of cold-rolling strain-paths on the microstructure, texture and mechanical properties of alloy Ni-16Cr-8Fe

In this work, the effect of variation of cold-rolling strain-paths (one-directional (U), two-stage cross (T), and multi-stage cross (M) rolling) on the evolution of microstructure as well as texture and their correlation with mechanical properties of alloy Ni-16Cr-8Fe has been studied. The overall texture strengthens while increasing rolling reductions from 30-to-50 and 50-to-90 % in all the strain-paths. In U strain-path, two of the standard rolling components—copper and brass—are strengthened significantly, while in T and M strain-paths only brass component strengthens. The overall texture has strong relationship with the brass-component of β-fibre irrespective of the strain-paths used during cold-rolling. The strain-path plays an important role in the changeover of texture from metal- to alloy-type, unlike what was previously thought that lowering of alloy’s stacking fault energy is the only reason. The yield (σYS) and tensile (σUTS) strength of 90 % rolled samples are significantly higher in U as compared to T and M strain-paths. The flow curves of 90 % rolled alloy follow Ludwigson-relationship with negative deviation in all the strain-paths. Regardless of the strain-paths, the area of yield locus ellipse increases as the rolling reductions are increased from 30-to-50 and 50-to-90 % and bear a good relationship with the overall texture. The average in-plane anisotropy in yield stress is observed to be highest in U strain-path. The theory of relative resolved shear stress of fcc slip systems in presence of highest intensity texture component well explains the variation in the values of in-plane anisotropies.

Effect of orientation deviation on random vibration fatigue behavior of nickel based single crystal superalloy

Vibration fatigue refers to the failure of a structure that is repeatedly subjected to loads causing resonance. The vibration fatigue performance of DD6 single crystal superalloy, an anisotropic material, is significantly affected by its various crystal orientations. This study investigates the impact of different vibration signal intensities and orientation deviation angles on the vibration fatigue behavior of DD6 single crystal superalloy. The fracture surface of the specimen that failed due to vibration fatigue was examined using scanning electron microscopy. The findings reveal that the primary failure mode for vibration fatigue of DD6 single crystal superalloy is the dislocation motion on the {111} plane with the greatest resolved shear stress in the octahedral slip system. Moreover, various methods, including time domain and frequency domain methods, were employed to predict the random vibration fatigue life of DD6 single crystal superalloy with different orientation deviation angles. Finally, a New Model was established to consider the vibration signal intensity and crystal orientation deviation angle, which improved the sensitivity of the frequency domain method to the crystal orientation deviation angle under different vibration signal intensities. Compared to other methods, the New Model is more suitable for predicting the random vibration fatigue life of DD6 single crystal superalloy with different orientation deviation angles.

Multi-mechanism-based twinning evolution in machined surface induced by thermal-mechanical loads with increasing cutting speeds

Microstructural features are an important factor in the evaluation of machined surface integrity. In particular, twins and twin boundaries have a significant impact on the physical and mechanical properties of components. This study investigates twin boundary evolution mechanisms in the machined surface during orthogonal cutting of oxygen-free-high-conductivity copper with cutting speeds ranging from 125 m/min to 2000 m/min. Pertinent features including twin boundaries, grain morphologies, textures, etc. Are characterized by electron backscattered diffraction and transmission electron microscope. The results show that the machined surface is divided into the refined layer, the deformed layer, and the matrix. An abnormal gradient distribution of a 60°<111> twin boundary is discovered for the first time. Specifically, the annealing twins mostly diminish in the deformed layer and regenerate in the refined layer. In the refined layer, a temperature-dominated process of twin formation and dynamic recrystallization occur. In the deformed layer, the resolved shear stress along the twin system is calculated through a novel approach, which reveals the stress-induced detwinning mechanism. The results of this research are beneficial for understanding both the deformation mechanism of medium stacking fault energy face-centered cubic metal under extreme loading conditions and the underlying effects of twins on the mechanical properties of machined surface.

Revealing the effect of misorientation on the deformation behavior of a Mg-Y alloy from the perspective of local strain

The addition of rare earth (RE) elements in magnesium alloys may significantly enhance the ductility of magnesium alloys, which is generally attributed to the decrease of stacking fault energy, the reduced critical resolved shear stress (CRSS) differences among different deformation modes and the weakening of basal texture. Rare earth elements also change the misorientation between adjacent grains of magnesium alloy, whose effects on the deformation behavior and thus the ductility of magnesium alloy were not emphasized before. In this work, ex-situ high-resolution digital image correlation (HR-DIC) coupled with electron backscatter diffraction (EBSD) was used to reveal the effect of the misorientation on the deformation behavior of a Mg-Y binary alloy from the perspective of local strain. It is shown that the heterogeneity of local strain is largely dependent on the misorientation between adjacent grains. For the intergranular deformation, three scenarios are observed, namely strain transfer, strain concentration and suppressed deformation, which mainly occurs at low misorientation, moderate misorientation and high misorientation, respectively. In addition, much more non-basal slip is found to be activated near the grain boundaries with moderate misorientation angles due to the high geometric compatibility factor (m’B-Pr/Py), which is favorable for the intergranular deformation compatibility, thus reducing the strain concentration near grain boundaries and achieving high ductility. For the intragranular deformation, a wide range of misorientation between adjacent grains in the Mg-Y alloy causes multiple basal slip systems to be activated within a grain, which also facilitates work hardening, thus contributing to improving ductility. Therefore, tailoring the misorientation between adjacent grains may be an effective way to improve the ductility of magnesium alloys.

The slip tendency of 3D faults in Germany

Abstract. Fault reactivation potential is a crucial aspect for many underground utilizations, such as the construction and long-term safety of a nuclear waste repository, as seismic events can endanger these operations. An estimation of the fault reactivation potential requires information about the stress field, but stress data are only available pointwise and are not evenly distributed throughout Germany. Geomechanical–numerical modeling can be used to derive a spatially continuous description of all six independent components of the stress tensor as shown by the model of Germany by Ahlers et al. (2022). Information about the geometry of faults extending several kilometers in depth is provided for most areas in Germany by the geological models of the federal states and geological models created in the framework of projects such as GeoMol (Assessing subsurface potentials of the Alpine Foreland Basins for sustainable planning and use of natural resources) or GeORG (Geopotenziale des tieferen Untergrundes im Oberrheingraben). We use the 3D fault geometries provided by such models and map the stress data from the Germany model by Ahlers et al. (2022) onto these faults. Then, assuming hydrostatic pore pressure, we calculate the so-called slip tendency (TS), the ratio between resolved shear stress and the effective normal stress on the fault plane as a measure of fault reactivation potential. A fault is considered critical when its TS value exceeds its coefficient of friction. In general, TS ranges between 0 and 0.7 for the analyzed faults. The highest overall TS values are observed along the NNE–SSW-striking Upper Rhine Graben, where TS routinely reaches and exceeds values of 0.7. In the North German Basin, the Ore Mountains and Saxony only very few TS values exceed 0.7. The area with the lowest overall TS is the Molasse Basin, where the TS of the mostly WSW–ENE-striking faults only rarely exceeds values of 0.4. In general, N–S- to NNE–SSW- and NW–SE-striking faults show the highest TS values, whereas WSW–ENE-striking faults show the overall lowest values. With increasing depth, TS decreases. Pore pressure and overpressure have the potential to significantly influence the resulting TS.

Room-temperature deformation of single crystals of WC investigated by micropillar compression

The room temperature deformation behavior of single crystals of WC has been investigated as a function of crystal orientation and specimen size by micropillar compression tests. Plastic flow is successfully observed at room temperature by the operation of slip on {011¯0}〈21¯1¯3〉 when the specimen size is reduced to micrometer orders. This slip system is the only operative slip system in WC at room temperature, and thus plastic flow is not observed for crystal orientations close to the c-axis orientation. The bulk critical resolve shear stress (CRSS) is estimated to be 1.2 ± 0.3 GPa from the extrapolation of the size-dependent CRSS. The 1/3〈21¯1¯3〉 dislocation carrying slip on {011¯0} dissociates into two identical collinear partial dislocations separated by a stacking fault with the energy of 211∼264 mJ/m2. The preference of slip along 〈21¯1¯3〉 among possible directions (such as 〈21¯1¯0〉 and [0001]) on the {011¯0} prism plane is discussed in terms of dislocation self-energy based on anisotropic elasticity, stacking fault energy, dislocation dissociation and Peierls stress for dislocation motion. The lowest Peierls stress arising from the shorter Burgers vector (1/6〈21¯1¯3〉) of dislocations as a result of collinear dissociation of dislocations with b = 1/3〈21¯1¯3〉 on the {011¯0} slip plane is considered to be the main reason for the preference of the {011¯0}〈21¯1¯3〉 slip system.

Molecular Dynamics Simulation of Interaction between Edge Dislocations and Stable β‐Phase Precipitates in Aluminum Alloy

Stable precipitate takes the essential role for material strengthening in Al–Mg–Si alloys. To reveal how the stable precipitate works in material strengthening, a molecular dynamics model is carried out to show the interaction between the edge dislocations and the plate‐shaped β phase of Mg2Si. The critical resolved shear stress (CRSS) is related to the precipitate characteristics including sizes and thickness directions. The CRSS increases with the increase of the precipitate size. When the thickness direction of precipitate changes from [001] to [100], the CRSS increases from 326.76 to 368.7 MPa. This phenomenon is mainly affected by the interaction length between dislocation and β phase. With the increase of interaction length, the interaction time for dislocation to overcome pinning increases. The critical bending angle of dislocation can be affected by the interaction time and shear strain rate. The relationship between the critical bending angle and the CRSS in Al–Mg–Si alloy is then established.

Effects of lamellar α orientation on the mechanical behavior of Ti–6Al–4V alloy manufactured by electron beam directed energy deposition

Crystallographic texture of alloy can trigger anisotropic properties, which have been studied extensively. However, the effect of spatial orientation of grains on the mechanical properties, especially for additive manufactured metals with lamellar morphology has remained elusive. Herein, this work theoretically calculated the spatial and crystallographic orientations of α lath from the <100>β//Z-axis (build direction) fiber texture, and investigate the relationship between the orientations of α lath and the deformation behaviors and mechanical properties of the Ti–6Al–4V alloy built via electron beam directed energy deposition (EB DED). Deformation features display the prismatic slip system of α lath that exists a smaller angle to the broad face of α lath showing a lower effective critical resolved shear stress (CRSS). This is because this prismatic slip system has a greater slip range when compares with other slip systems. Such deformation features, combined with the spatial orientation distribution characteristic of α lath that is induced by the <100>β//Z-axis fiber texture, lead to strongly tensile anisotropy, specifically, the samples oriented 45° and 67.5° angles to z-axis present greater strengths but lower ductility, whereas the sample in the z-axis direction generally displays a minimum strength but a superb ductility. This finding is vital for providing an important theoretical basis for optimizing the consistency of mechanical properties of the additive manufactured α+β dual phase titanium alloy.

Increasing the friction stress decreases the size dependence of strength in a family of face-centered cubic high- and medium-entropy alloy micropillars

Size effects (‘smaller is stronger’) are important aspects of the mechanical behavior of materials. Experimentally, they are usually probed by performing compression tests on micropillars of different sizes (cross-sectional areas). To overcome limitations associated with comparing different crystal structures and to better handle the influence of melting points in different metals, single crystal face centered cubic (fcc) micropillars of equiatomic binary, ternary, and quaternary medium-entropy alloy (MEA) subsystems of the quinary CrMnFeCoNi high-entropy alloy (HEA) were tested. All eight alloys investigated were single-phase solid solutions having the fcc crystal structure. Their melting temperatures varied only over a narrow range (1189-1462 °C). They exhibit a size-dependent critical resolved shear stress (CRSS ∝ d-n, where d is the pillar diameter, n is a power law exponent). The results show that, all else being equal, size effects scale inversely with friction stress. In contrast, there is no systematic dependence on configurational entropy, contrary to speculations in some earlier papers that solid solution strengthening would increase as the number of alloying elements increases. ‘Bulk’ CRSS values were estimated by extrapolating the measured CRSS values of pillars with diameters of approximately 1-8 μm to larger pillar sizes of 30 μm. Good agreement was found with available CRSS values of bulk single crystals. It is concluded that it is possible to obtain bulk CRSS values more reliably from micropillar tests than from the Taylor factor corrected yield strengths of bulk polycrystals.

Plastic deformation of single crystals of the equiatomic Cr-Fe-Co-Ni medium entropy alloy – A comparison with Cr-Mn-Fe-Co-Ni and Cr-Co-Ni alloys

The plastic deformation behavior of single crystals of the equiatomic Cr-Fe-Co-Ni medium-entropy alloy was investigated in compression and tension from 9 K to 1373 K. The critical resolved shear stress (CRSS) for {111}<11¯0> slip is 44–45 MPa at room temperature and does not exhibit significant tension-compression asymmetry. It increases rapidly with decreasing temperature but exhibits a dulling of the temperature dependence below 77 K due to the inertia effect. The 0 K CRSS was determined to be 200 MPa by extrapolating the temperature dependence of CRSS from above 77 K to lower temperatures. This CRSS value is higher than that of the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy, 174 MPa, but lower than that of the equiatomic Cr-Co-Ni medium-entropy alloy, 225 MPa. The rank of CRSS at 0 K of the three equiatomic alloys is consistent with the prediction of some solid solution strengthening models. The stacking fault energy (SFE) of the Cr-Fe-Co-Ni is about 20 mJ/m2, which falls between those of the Cr-Mn-Fe-Co-Ni and Cr-Co-Ni alloys. Deformation twinning in the Cr-Fe-Co-Ni MEA occurs at a shear stress of 249 MPa on conjugate (1¯1¯1) planes in the form of Lüders deformation at 77 K. The relationship between twinning stress and SFE is not monotonic as previously believed, but displays a concave with a minimum twinning stress at an intermediate SFE value.

A comparative study of deformation behaviors and ductility improvement in Mg–Gd–Zr and Mg–Zr cast alloys

This study investigates the impact of Gd elements on the enhancement of ductility in the Mg–Gd–Zr alloy. The deformation behavior at room temperature of the cast Mg–Gd–Zr alloy and the cast Mg–Zr alloy was examined using the EBSD-assisted slip trace method. The quantitative analysis of the initiation ratio of each slip system in the two alloys revealed that the Mg–Gd–Zr alloy had a higher ratio of non-basal slip systems. The experimental determination of the critical resolved shear stress (CRSS) ratios of non-basal slip to basal slip for both alloys indicated that the Gd elements could reduce this ratio, facilitating the initiation of more non-basal slip systems to accommodate strain. Furthermore, the segregation of Gd elements at grain boundaries was observed to enhance the grain boundary strength of the alloy, which is a significant factor in the enhancement of ductility.