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Understanding the mechanical behavior of nanotwinned materials in alloys is essential, particularly in relation to solute-influenced twin boundary (TB) migration. This research employs atomistic simulations and theoretical analysis to explore the influence of solute atoms on TB migration in CuAg alloys. Contrary to conventional beliefs, simulations reveal that solute Ag atoms enhance TB migration, challenging established perceptions. Nudged elastic band calculations confirm that Ag solutes substantially reduce energy barriers, shedding light on the mechanism driving solute-enhanced TB migration. This work opens novel avenues for investigating point defect impacts on TB mobility, offering insights into alloy element roles in grain boundary migration and polycrystalline material properties. [ABSTRACT FROM AUTHOR]

Porous Ni–Mn–Ga shape memory alloy with the pore size of 20–30 μ m was fabricated by the powder metallurgy with the pore-forming agent of NaCl. The prepared alloy has a uniform pore distribution and a complete sintering neck, which reduces the number of grain boundaries. Pores constrain the transmission of stress, leading to stress concentration, which decreases the critical stress of martensitic twin variants reorientation (<10 MPa). Meanwhile, the strength of porous alloys can be tuned by the alloying of Ti. In addition, the porous Ni–Mn–Ga alloy obtained a lower critical stress for martensitic twin boundary motion after cyclic compression, which makes it suitable for devices that require energy absorption under low stress. The microstructure and mechanical properties of Ni–Mn–Ga porous alloy were analyzed, and the effects of pores on the Ni–Mn–Ga alloy were also discussed. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to investigate the corrosion resistance of Fe‐36Ni Invar alloys with varying Mg contents in a 3.5 wt% sodium chloride solution. The electrochemical results reveal that the incorporation of Mg amplified the corrosion behavior of Fe‐36Ni Invar alloy. The inclusion compositions undergo a transformation with the increase of Mg content, evolving from MnO–MnS in 0 Mg alloy to MnO–MnS–MgO in 0.0015 Mg alloy, and ultimately to MnS–MgO–MgS in 0.0030 Mg alloy. During the corrosion process, the small‐sized MnS–MgO–MgS inclusions exhibit greater stability compared to the MnO–MnS inclusions, rendering them less susceptible to attack and dissolution. Adding Mg diminishes the size and number density of inclusions, which effectively decreases the susceptibility to pitting initiation. The introduction of Mg refines the microstructure and elevates the fraction of twin boundaries, which also is responsible for the enhancement of corrosion resistance. [ABSTRACT FROM AUTHOR]

FeCoCrNiCu high-entropy alloys (HEAs) exhibit extraordinary mechanical properties and have the capability to withstand extreme temperatures and pressures. Their exceptional attributes make them suitable for diverse applications, from aerospace to chemical industry. We employ atomic-scale simulations to explore the effects of twinning boundary and twinning thickness on the mechanical behavior of nanotwinned FeCoCrNiCu during nanoindentation. The findings suggest that as the twinning thickness decreases within the range of 19.3–28.9 Å, both twinning partial slips (TPSs) and horizontal TPSs gradually become dominant in governing the plastic behaviors of the nanotwinned FeCoCrNiCu, thereby resulting in an inverse Hall–Petch effect. Remarkably, when the twinning thickness is compressed below 19.3 Å, a shift in the plastic deformation mechanism emerges, triggering the conventional Hall–Petch relation. The observed Hall–Petch behavior in nanotwinned FeCoCrNiCu is attributed to the strengthening effect imparted by the twinning boundaries. Consequently, the twinning boundary play an instrumental role in steering the plastic deformation mechanism of the nanotwinned FeCoCrNiCu when the twinning thickness descends beneath 19.3 Å. This study contributes significant insights towards the design of next-generation high-performance HEAs, underpinning their potential industrial utilization. [ABSTRACT FROM AUTHOR]

Previous work shows that a maximal recovery strain of 8.4% after being bent at room temperature is realized in annealed cast polycrystalline Fe–Mn–Si‐based alloys because of the reduced annealing twin boundaries. Theoretically, higher recovery strains can be expected at cryogenic deformation by reducing thermal activation. To confirm this idea, martensitic transformation behaviors and the recovery strains after being bent at 77 K are investigated in the cast Fe–(20–26)Mn–5.5Si–8.5Cr–5Ni alloys. Herein, larger recovery strains as high as ≈10.0% are realized in an annealed cast Fe–23Mn–5.5Si–8.5Cr–5Ni alloy after being bent at 77 K. The reduced thermal activation together with suppressed formation of thermal‐induced martensite by optimizing Mn content can account for the larger recovery strain. In these results, a new avenue is opened up for further enhancement of the recovery strain in Fe–Mn–Si‐based shape memory alloys. [ABSTRACT FROM AUTHOR]

The application of shape memory alloys is very suitable for developing pipe joints, and Fe-Mn-Si memory alloy pipe joints show great promise. This paper studied the variation rule and microscopic mechanism of the strain recovery rates of Fe-24Mn-6Si-7Cr-3Ni alloy pipe joints made by three different hot working technologies: casting, forging, and rolling. The strain recovery rate of as-cast pipe joints rose monotonously with the increasing thermomechanical training cycle. As-cast pipe joints' superior shape memory effect mainly came from the large grain size of 662.70 μm and the low density of annealing twin boundaries. On the other hand, the shape memory effects of forging and rolling pipe joints were restricted by the high densities of annealing twin boundaries and grain boundaries, respectively. Although the shape memory effects had a lower upper limit, their strain recovery rates climbed quickly. Following the third annealing, the remaining second-phase particles precipitated according to the ε -martensitic distribution orientation, and this contributed to the shape memory effects of as-cast and forging pipe joints. During adjusting the solution treatment parameters for as-cast pipe joints, it was found that as-cast pipe joints without solution treatment exhibited a notable superiority over the solution-treated ones when less thermomechanical training was performed. [ABSTRACT FROM AUTHOR]

This study employed molecular dynamics (MD) simulation to investigate the mechanical behavior of copper–silver (Cu–Ag) nanocrystalline alloys with twinning structures under solute gradient polarization conditions. The equidistant scaling method was used to identify different regions within the material, such as the solute concentration distribution from the grain interior to the GBs (GBs). MD simulations revealed that adjusting the twinning boundary spacing (TBS) can effectively improve the mechanical properties of Cu–Ag alloys. Tensile tests showed that stretching the twinning boundaries leads to a reduction in stress levels within the alloy. Furthermore, analysis based on the atomic structure volume fraction revealed that larger TBS values result in more pronounced structural changes within the alloy, particularly a significant transition from the face-centered cubic structure to the hexagonal close-packed structure. The latter typically possesses a higher density and closer packing, thus often exhibiting a higher strength and hardness. These findings reveal that adjusting the grain size, segregation gradients, TBS, and grain number can effectively improve the mechanical properties of Cu–Ag alloys. [ABSTRACT FROM AUTHOR]

Due to its characteristic of low stress brittle fracture, hydrogen embrittlement (HE) is a great challenge for the alloys exposed to hydrogen-containing environments, threatening the safety and integrity of structural components. The physical and chemical status of the interfaces, among which grain boundary (GB), twin boundary (TB), and matrix/nano-precipitate interfaces (coherent, semi-coherent, and incoherent) are the representative ones, play a crucial role in determining the HE susceptibility of materials. Hence, this study mainly reviews recent progress in the interaction between hydrogen and these interfaces, i.e., 1) hydrogen-GB interaction (dominant HE mechanisms, crystallographic features of hydrogen-assisted intergranular cracking, and the strategies for resisting HE through GB segregation and GB engineering); 2) hydrogen-TB interaction (the effect of deformation/pre-existing twins on HE susceptibility, four types of TB-related cracking mechanisms, and the improvement of HE-tolerance by the control of pre-twins, gradient-twins, and twin orientations); and 3) hydrogen-precipitate interaction (hydrogen capacity, hydrogen trapping sites, hydrogen activation energy, and the effect of nano-precipitates on HE of alloys). The correlation between HE susceptibility, active HE mechanisms and their synergy (HELP + HEDE model), and three types of interfaces have been comprehensively summarized and discussed. Also, the strategies for the improvement of HE resistance are proposed in terms of the control of these microstructural interfaces in metallic alloys. [Display omitted] • Effect of the interfaces on hydrogen embrittlement (HE) of alloys is reviewed. • Hydrogen-assisted interface cracking mechanisms of alloys is summarized. • Strategies for resisting HE are proposed through the control of the interfaces. • Semi-coherent precipitates are suggested to balance strength and HE-resistance. [ABSTRACT FROM AUTHOR]

Although the influence of grain boundaries (GB) or twin boundaries (TB) on corrosion resistance has been studied, there is no comparative study addressing the corrosion behavior of the two types of grain refinement. In this work, a comparative study of the corrosion behavior of samples with coarse grains (GB-coarse), fine grains (GB-refined), twin boundaries (TB-refined), and twin boundaries with solute atoms (TBS-refined) has been made. Results indicate that grain boundary refinement is more effective than twin boundaries in improving the corrosion resistance when grains are refined to similar grain sizes. The GB-refined sample show a typical corrosion band along rolling direction, while the corrosion in TB-refined counterparts preferentially occurs in twins. Twin boundaries improve corrosion resistance exclusively at an early stage, while an increase in corrosion rate after immersion occurs at longer times. In addition, segregation of solute atoms at twin boundaries further contributes to improving corrosion resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Twinning in Mg alloys arises due to challenges in slip along the c-axis, impacting orientations differently at varying CRSS. • Many factors like GBs, texture, and stress states influence the twinning nucleation, propagation, and growth in Mg alloys. • Dislocation interactions and thermal effects affect twinning activation in Mg alloys, while annealing treatments may stabilize TBs. • Anomalous behavior of ET in Mg-RE alloys suggests RE elements alter c/a ratio, favoring smaller Burger vector at TBs. • CT and DT in Mg alloys promote DRX but pose risks as sources of voids and cracks. Twinning is widely recognized as an effective and cost-efficient method for controlling the microstructure and properties of wrought magnesium (Mg) alloys. Specifically, twins play a crucial role in initiating dynamic recrystallization (DRX), while twin regions experience rapid recrystallization during static recrystallization (SRX). The activation of twinning can lead to changes in lattice orientation, significantly impacting the final texture in Mg alloys. The active roles of twinning are influenced by various factors during the activation process, and the mobility of twin boundaries (TB) can be amplified by stress effects, dislocation interactions, and thermal effects. Conversely, annealing treatments that involve proper segregation or precipitation on TBs serve to stabilize them, restraining their motion. Events such as segregation may also alter the twinning propensity in Magnesium-rare earth (Mg-RE) alloys. While {10–11} contraction twins (CT) and {10–11}-{10–12} double twins (DT) can promote dynamic recrystallization (DRX), they also pose a risk as potential sources of voids and cracks. Additionally, understanding the nucleation and growth mechanisms of twinning is crucial, and these aspects are briefly reviewed in this article. Considering the factors mentioned above, this article summarizes the recent research progress in this field, shedding light on advancements in recent eras. [ABSTRACT FROM AUTHOR]

Multi-element alloys (e.g., non-equiatomic FeMnCoCr alloys) have attracted extensive attention from researchers due to the breaking of the strengthen-ductility tradeoff relationship. Plenty of work has been conducted to investigate the ingredient-dependent deformation mechanism in these alloys in experiments. However, the atomic simulations on such parameter-related mechanisms are greatly limited with the lack of the related interatomic potentials. In this work, two interatomic potentials are developed within the embedded atom method (EAM) framework for Fe80−xMnxCo10Cr10 high-entropy alloys. The tunability of the cohesive energy-related martensitic transformation (MT) mechanism was comprehensively investigated using molecular dynamics (MD) through a series of unilateral crack configurations with different twin boundary spacings (TBs). It is noted that the main deformation mechanism around the crack tip is transformed from a martensitic transformation to dislocation activities (dislocation or twin) with the variation of different cohesive energies between face-centered cubic (fcc) and hexagonal close-packed (hcp) phases. Additionally, the introduction of twin boundaries significantly enhances the strength and toughness of the alloys. The newly developed interatomic potentials are expected to provide theoretical support for the related simulations, focusing the martensitic transformation mechanism on high-entropy alloys. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) break the design concept of traditional alloys and exhibit excellent mechanical properties. However, as a new member of the alloy family in recent years, the dependence of the deformation behavior of the HEAs on alloy composition and twin boundary (TB) is still unclear, and many phenomena urgently need to be revealed. Here, the effects of TB spacing and Ni concentration on the mechanical properties and deformation behavior of the nano-twinned (CoCrFeCu)1−XNiX HEA (nt-HEA) under tensile loading are investigated by molecular dynamics simulation. The results show that with the decrease in TB spacing, the average flow stress of the nt-HEA changes from Hall–Petch strengthening to inverse Hall–Petch softening. When the TB spacing is greater than a critical value, the plastic deformation mechanism is dominated by the slip of partial dislocations. However, when the TB spacing is less than the critical value, the plastic deformation mechanism is transformed into the formation of voids induced by the amorphous phase, which becomes the key factor for the softening of the nt-HEA. It is also found that the mechanical properties of the nt-HEA can also change from strengthening to softening by adjusting Ni concentration, which is closely related to the change of stacking fault energy of the nt-HEA. In addition, the plastic deformation mechanism and voids formation mechanism of the nt-HEA are also discussed in detail. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation was applied to investigate the interaction between precipitate and 10 1 ¯ 2 twin in Mg-Al alloy in this work. Three sets of simulation including twin nucleation, propagation and growth affected by precipitate were performed. The results show the introduction of precipitate has little effect on neither the homogeneous twin nucleation at random site inside the grain nor the heterogeneous nucleation at grain boundary. During twin propagation, the blocking effect of precipitate to the twin tip depends on its size. The twin tip can bypass the precipitate when the precipitate is not long enough. When the length of precipitate is much larger than the thickness of twin, the twin tip will be completely blocked by the precipitate with elastic bending occurring at the junction. During the twin growth, it is found that the precipitate plays not only an obstacle but a source for the twinning dislocations gliding along the twin boundary. The blocking effect of precipitate on twin growth shows a size effect. The influences of width and thickness on precipitation hardening are significantly greater than that of length. [ABSTRACT FROM AUTHOR]

Modifying the gain orientation is considered a crucial method for enhancing the corrosion resistance of Mg alloys. This study aims to improve the corrosion properties of AZ31 alloy sheet through pre-stretch deformation, specifically compression (6.8%) along the extrusion direction (ED). To eliminate the twin structure, a recrystallization annealing process was performed after the pre-stretch deformation. To investigate the corrosion performance of Mg alloys, we conducted electrochemical and hydrogen evolution tests, which provided insights into the influence of microstructure on the corrosion resistance of Mg alloys. The results indicate that the corrosion resistance was altered by the presence of twin grain boundaries that formed after pre-stretch deformation. Furthermore, the recrystallized texture with//ED orientation exhibited the highest corrosion resistance, underscoring the significant role played by grain orientation. [ABSTRACT FROM AUTHOR]

The high Sc-alloyed Al–Sc sputtering target is applied to produce Sc-doped AlN (Al1−xScxN) thin films through reactive magnetron sputtering. The sputtering process demands Al–Sc sputtering targets with fine and stable grain sizes featuring random orientations. In this work, laser treatment with varying scanning speeds is applied to the Al-(10 at.%, 20 at.%) Sc alloys, and the microstructure is characterized using the electron backscatter diffraction (EBSD) method and transmission electron microscopy (TEM). The results indicate that the laser treatment enhances the solubility of Sc in the matrix; however, the nucleation crystallography during solidification differs among these alloys. Epitaxial growth is observed in Al–20Sc, remaining a large grain size with different scanning speeds. In contrast, Al–10Sc exhibits refined grain sizes, reduced to about 2 μm compared to 200 μm in the as-casted alloy. Laser treatment generates more than 40% twin boundaries, leading to the randomization of the texture and refinement of the grain size through twin variants. This study demonstrates the feasibility of grain boundary engineering for Al–10Sc sputtering targets through laser scanning. [ABSTRACT FROM AUTHOR]

To investigate the impact of Twinning Boundary Spacing (TBS) on the mechanical characteristics and deformation behavior of nanotwinned Cu–Ag alloys with solute gradient segregation structure during nanoindentation, Voronoi's method is utilized to create a nanotwinned Cu–Ag alloy model with solute gradient segregation structure. Then, the indentation process of the indenter pressed into the model with varying TBS is simulated using the Molecular Dynamics (MD) simulation, yielding depth-stress curves of the corresponding indenter. According to the findings, yield stresses are lower in Cu–Ag alloys with smaller twin spacing. Grain boundary activities play a governing role in the plastic deformation of the matrix during the small deformation stage, although dislocations also play a part. Grain boundaries have less of an impact on material deformation during the big deformation stage, and dislocations are primarily responsible for the matrix's plastic deformation. The stacking faults and deformation twin are more prone to occur inside grains with higher solute-atom concentrations compared to grain boundaries with lower solute-atom concentrations. Nanotwinned Cu–Ag alloy with solute atomic gradient segregation was constructed. An atomic-scale view of deformation progress by molecular dynamics simulation was presented. The mechanical behavior of nanotwinned Cu–Ag alloy can be effectively improved by adjusting the solute concentration distribution and twin boundary spacing. [ABSTRACT FROM AUTHOR]

Precipitation strengthening is a key strategy for improving the overall mechanical properties of Mg alloys. In Mg-Al alloys, basal precipitates are known to strengthen against twinning, resulting in an increase in the critical resolved shear stress (CRSS) necessary for continued deformation. Although several models have been proposed to quantify the influence of precipitate shape, size, and distribution on the CRSS, the accuracy, scope, and applicability of these models has not been fully assessed. Accordingly, the objectives of this study are: (i) to analyze the accuracy of analytical models proposed in the literature for precipitation strengthening against twin thickening and propagation (in Mg-Al alloys) using phase-field (PF) simulations, (ii) to propose modifications to these model forms to better capture the observed trends in the PF data, and (iii) to subsequently test the predictiveness of the extended models in extrapolating to experimental strengthening data. First, using an atomistically-informed phase-field method, the interactions between migrating twin boundaries (during the propagation and thickening stages) and basal plates are simulated for different precipitate sizes and arrangements. In general, comparison of the increase in CRSS determined from the PF simulations and the predictions from four precipitation strengthening models reveals that modifications are necessary to the model forms to extend their applicability to precipitation strengthening against both twin thickening and propagation. A subsequent comparison between predictions from the extended models and experimental strengthening data for peak age-hardened samples reveals that the (extended) single dislocation and dislocation wall models provide reasonably accurate values of the increase in CRSS. Ultimately, the results presented here help elucidate the fidelity and applicability of the various hardening models in predicting precipitation strenghtening effects in technologically important alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

To overcome the trade-off between strength and ductility, a low-cost method comprising room-temperature compression followed by artificial aging and compressive deformation was applied to a commercial AZ61 alloy. The goal of this work was to regulate the microstructure rather than refine the grains. For this purpose, fragmented precipitates decorating the boundaries of narrow twins and stable networks developed by two non-basal slip systems were achieved. With this novel microstructure, a highly improved yield strength of almost 120 MPa was realized with slightly decreased ductility. It is believed that this provides a novel orientation for rationally designing strength and ductility in age-hardenable Mg alloys by tailoring the precipitate scale and dislocation configuration. [ABSTRACT FROM AUTHOR]

Incoloy 800H alloy has excellent high-temperature mechanical properties and broad application prospects. However, the dynamic recrystallization (DRX) behavior of this alloy at different deformations has been little studied. The thermal deformation characteristics and DRX mechanisms of Incoloy 800H alloy are studied by thermal compression tests. Quantitative analysis of grain size, DRX fraction, misorientation distribution, and twin boundaries under different deformation degrees is conducted using electron-backscattered diffraction. Furthermore, the evolution characteristics of dislocations and grains are observed through transmission electron microscopy. It is found that the proportion of DRX improves with increasing deformation significantly. In the DRX process, discontinuous DRX (DDRX) is the main nucleation mechanism, while continuous DRX (CDRX) serves as an auxiliary nucleation mechanism. As the deformation increases, the CDRX þ DDRX mechanisms can also be observed simultaneously in the high-density dislocation region near the grain boundary. In addition, the ratio of Σ3 boundaries first decreases and then increases as the deformation increases. The initial twins gradually disappear due to the increase in deformation, and new twins are formed within the DRX grains. Twins can promote grain boundary bulging, provide more nucleation sites for DRX, and have a significant promoting effect on DRX. [ABSTRACT FROM AUTHOR]

• The importance of grain refinement in improving strength of Mg alloys has been demonstrated. • The DRX models and DRX mechanisms and the related grain refinement ability are summarized. • The mechanical property enhancement by grain refinement strategy of newly developed low-RE containing Mg alloy and the RE-free Mg alloys are reviewed. • The perspectives and outstanding issues concerning high-performance Mg wrought alloys are proposed. Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth (RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization (DRX) plays a crucial role in refining grain size of Mg wrought alloys. Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized, including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy, are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing. [ABSTRACT FROM AUTHOR]

Twinning-mediated plasticity has great potential for enhancing the strength and plasticity of Mg alloys, which is limited due to the lack of twin types. Here, we report a novel multistage twinning mode, i.e. the dominant twinning mode changes from single { 10 1 ¯ 2 } twins to the co-existence of { 10 1 ¯ 2 } and { 11 2 ¯ 6 } twins, in a deformed Mg-Al-Gd alloy. Introducing novel multistage twinning mode to accommodate strains appreciably along c-axes, combined with the interactions of high-density dislocations and dense twin boundaries, guarantees the high strain hardening of Mg alloys. These findings provide new insights into deformation mechanisms and mechanical properties of Mg-alloys. Introducing novel multistage twinning mode to accommodate strains appreciably along c-axes, combined with the interactions of high-density dislocations and dense twin boundaries, guarantees the high strain hardening of Mg alloys. [ABSTRACT FROM AUTHOR]

Using the molecular dynamics simulation method, nanoindentation simulation was carried out on a variety of nanotwin Cu-Ag alloys with different gradient distribution structures and twin spacing to study the mechanical properties and deformation mechanism of nanotwin Cu-Ag alloys with a grain size of 15 nm. The deformation, failure process, and microstructure evolution of the model during extrusion were defined and analyzed by means of common neighbor analysis (CNA) and dislocation analysis (DXA), and the micro-mechanism of twin spacing and solute atom gradient segregation structure affecting the mechanical properties of nanotwin Cu-Ag alloy was revealed. The results show that different solute atom gradient segregation structures and twin spacing have important effects on the mechanical properties of nanotwin Cu-Ag alloy. Dislocations and stacking faults are more likely to occur within grains with thicker solute concentrations and larger twin boundary spacing. [ABSTRACT FROM AUTHOR]

The raw materials for extruded preparing magnesium alloy tubes were electromagnetic stirring (EMS) AZ31 magnesium alloy billets and conventional casting (CC) AZ31 magnesium alloy billets. According to the findings, the mechanical properties of the EMS extrusion tubes were far superior to those of the CC extrusion tubes. The key explanation was that the samples of EMS billet had variable initial grain sizes and twin boundaries, which provide additional nucleation sites for DRX nucleation during the extrusion process. With the increase of extrusion temperature and extrusion ratio, the elongation of the tube is further improved. During the extrusion process, the recrystallization mechanism changed from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX). [ABSTRACT FROM AUTHOR]

Grain boundary engineering is an effective and feasible metal strengthening strategy to enhance the properties of nanopolycrystalline alloys by changing the number, configuration, and connectivity of different types of grain boundaries, especially for the twin boundaries. In the present contribution, the effect of twin spacing and loading mode on the deformation behavior and mechanism of NiCoAl columnar polycrystalline alloy is investigated. The results show that the nanotwins can not only increase the bearing capacity of dislocations but also emit many dislocations, resulting in the coupling effect of dislocation strengthening and twin strengthening. When the twin spacing is large, intrinsic stacking faults occur and gradually transform into deformation twins. In this stage, Shockley partial dislocation controls plastic deformation. When the twin spacing is small, the high‐density twin layers and stacking faults are more likely to interweave, showing a combination action of Shockley partial dislocation and stair‐rod dislocation. With the loading changing to Z axis, the yield strength decreases due to reduced resistance to the dislocation and a weakened number of Shockley partial dislocations of the emission, leading to less strengthening of the twins. The insights provide a solid theoretical foundation for the further application of NiCoAl in industrial production. [ABSTRACT FROM AUTHOR]

The dynamic spheroidization mechanism and its orientation dependence in Ti-6Al-2Mo-2V-1Fe alloys during subtransus hot deformation were studied in this work. For this purpose, hot compression tests were carried out at temperatures of 780–880 °C, with strain rates of 0.001–0.1 s−1. Based on SEM, EBSD and TEM characterization, the results showed that the aspect ratio of the α phase decreased with increasing deformation temperatures and decreasing strain rates. At 880 °C/0.001 s−1, the aspect ratio of the α phase was the smallest at 2.05. The proportion of HAGBs decreased with increasing temperatures and strain rates, which was different from the trend of the spheroidization; this indicated that the formation of HAGBs was not necessary for the spheroidization process. Furthermore, the formation of the α/α interface was related to the evolution of dislocations and twin boundaries at high (880 °C) and low temperatures (780 °C), respectively. Moreover, the dependence of lamellar spheroidization on the crystallographic orientation tilt from the compression direction (θ) was clarified: when θ was between 45° and 60°, both the prism slip and basal slip systems were activated together, which was more favorable for spheroidization. This study could provide guidance for titanium alloy process designs and microstructure regulation. [ABSTRACT FROM AUTHOR]

This study investigates the variations in the microstructural characteristics of a pre-twinned Mg alloy with the temperature of the subsequent annealing treatment. To this end, a rolled AZ31 alloy is compressed to 3% plastic strain along the rolling direction (RD) to activate {10-12} twinning and is subsequently annealed at 200, 250, 300, 350, and 400 °C. Numerous {10-12} twins are formed throughout the compressed material, leading to the formation of a RD-oriented texture. At an annealing temperature of 200 °C, no microstructural variations occur during annealing. As the annealing temperature increases from 250 to 400 °C, the residual strain energy and remaining twin boundaries of the annealed material decrease owing to the promoted static recovery and the increased area fraction of twin-free grown grains. Consequently, an increase in the annealing temperature results in a gradual microstructural transition from a fully twinned grain structure to a completely twin-free grain structure. The microstructural evolution during annealing is predominantly governed by the movement of high-angle grain boundaries via a strain-induced boundary migration mechanism, and a few twin boundaries migrate above 350 °C because of their lower boundary energy. The boundary migration behavior and resultant microstructural evolution are discussed in detail based on the variations in boundary mobility and driving force for boundary migration with annealing temperature. [ABSTRACT FROM AUTHOR]

The effects of pre-twinning on the microstructure and dynamic compression properties of non-aged and artificially aged Mg–Y–Nd–Gd–Zr alloys were investigated in this study. Previous studies have shown that in the pre-deformed T3 alloy, precompression along the extrusion direction (ED) generates high-density < a > and < c + a > dislocations and deformation twins, such as the 10 1 ¯ 2 < 10 1 ¯ 1 ¯ > extension, the 10 1 ¯ 1 - 10 1 ¯ 2 double, and 10 1 ¯ 1 < 10 1 ¯ 2 ¯ > compression twins at 86°, 38°, and 56°, respectively. In the pre-deformed T8 alloy artificially aged at 200 °C for 12 h, the dislocation density was found to decrease, with β″ (Mg3Y0.85Nd0.15) and β′ (Mg12NdY) precipitates appearing at both ends of the twin boundary. Subsequently, the precipitates extended toward [0001]Mg and [0001]T in the matrix region and the twin, respectively. The orientation relationships (ORs) between the β″ and β′ precipitates and the matrix/twin were determined to be 01 1 ¯ 0 β ″ / / 0001 Mg / T , 2 1 ¯ 1 ¯ 0 β ″ / / 2 1 ¯ 1 ¯ 0 Mg / T and (001)β′//(0001)Mg/T, 2 1 ¯ 1 ¯ 0 β ′ / / 2 1 ¯ 1 ¯ 0 Mg / T , respectively, in contrast to the counterpart ORs between the β″ and β′ precipitates and the matrix/twin in the non-deformed T61 alloy. Evaluation of the dynamic compression properties showed that compared with the compressive yield strength (CYS) of the T61 alloy, that of the T8 alloy considerably increased from 220 to 339 MPa. However, their ultimate compressive strengths (UCSs) of 363 and 360 MPa, respectively, were similar owing to the synergistic effect between the dislocations, the twin boundaries, and the precipitates. These results suggest that the pre-twinning approach should be adopted to improve the strengths of magnesium alloys. [ABSTRACT FROM AUTHOR]

In this paper, we report an in situ study regarding the microstructural evolution of a nickel-based alloy with high proportional twin boundaries by using electron backscatter diffraction techniques combined with the uniaxial tensile test. The study mainly focuses on the evolution of substructure, geometrically necessary dislocation, multiple types of grain boundaries (especially twin boundaries), and grain orientation. The results show that the Cr20Ni80 alloy can be obtained with up to 73% twin boundaries by annealing at 1100 °C for 30 min. During this deformation, dislocations preferentially accumulate near the twin boundary, and the strain also localizes at the twin boundary. With the increasing strain, dislocation interaction with grain boundaries leads to a decreasing trend of twin boundaries. However, when the strain is 0.024, the twin boundary is found to increase slightly. Meanwhile, the grain orientation gradually rotates to a stable direction and forms a Copper, S texture, and α-fiber <110>. Above all, during this deformation process, the alloy is deformed mainly by two deformation mechanisms: mechanical twinning and dislocation slip. [ABSTRACT FROM AUTHOR]

{ 10 1 ¯ 2 } twins were introduced into the magnesium (Mg) plate AZ31 via pre-rolling along its transverse direction. The plates, both with and without the pre-induced { 10 1 ¯ 2 } twins, were subjected to uniaxial tension along different directions. Using crystal plasticity modeling, we found that the strengthening effect of the pre-induced { 10 1 ¯ 2 } twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries, rather than the orientation hardening due to the twinning reorientation (although the latter did make its contribution in some specific loading directions). Besides, the pre-existing { 10 1 ¯ 2 } twins were found, by both experiments and simulation, to promote the activity of prismatic 〈a〉 and pyramidal in the parent matrix of the material. Further analysis showed that the enhanced non-basal slip activity is related to the { 10 1 ¯ 2 } twin boundaries' low micro Hall-Petch slope ratios of non-basal slips to basal slip. With the critical resolved shear stress (CRSS) obtained from crystal plasticity modeling and the orientation data from EBSD, a probability-based slip transfer model was proposed. The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at { 10 1 ¯ 2 } twin boundaries than that at grain boundaries, which agrees with the experimental observation that the strain localization was primarily associated with the latter. The present findings are helpful scientifically, in deepening our understanding of how the pre-induced { 10 1 ¯ 2 } twins affect the strength and slip activity of Mg alloys, and technologically, in guiding the design of the pre-strain protocol of Mg alloys. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys are essential for industrial applications but poorly understood from a mechanistic perspective, while a comprehensive understanding of their mechanical behavior can guarantee a more efficient alloy design as well as a greater application potential. As one of the key deformation mechanisms in Mg and Mg alloys, twinning is investigated in this work. Molecular dynamics simulations are used to perform a systematic study of the effect of alloying elements and solute compositions on twin embryo growth in nine Mg alloys. The alloying elements include Al, Zn, Li, Ca, Pb, Nd, Ce, Sn, and Y, covering a wide range of element properties such as lattice constant, bulk/shear modulus, and cohesive energy. We demonstrate a faster migration of the dark side than the bright side of twin embryos in both pure Mg and Mg alloys. All solute atoms tested in this work exhibit a pinning effect on the motion of twin facets on the dark side. The motion of facets on the bright side, particularly twin boundaries, can be accelerated by solutes. Therefore, the majority of solutes can reduce the velocity difference between the dark side and the bright side of the twin. The overall twin embryo growth is restricted in most alloys except Mg–Y, Mg–Li and Mg–Nd with certain solute concentrations. Our results present important insight for tailoring twin structures and hence the mechanical properties of Mg alloys. [ABSTRACT FROM AUTHOR]

Heterogenous precipitation of the γ′ phase on different types of interfacial defects on {10 1 ¯ 2} twin boundaries in a Mg-Gd-Zn-Zr alloy has been systematically investigated using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, molecular dynamics simulations and first-principles calculations. Prior to precipitation, twin boundaries comprise a coherent twin boundary and various basal-prismatic/prismatic-basal interfacial defects. These defects include those associated with an I 1 stacking fault, dislocations with an extra half atomic plane oriented either normal or parallel to the interface, and defects without stacking faults or dislocations. During ageing, Gd and Zn atoms segregate to the I 1 stacking fault, the coherent twin boundary, interfacial defects lacking stacking faults or dislocations, and interfacial defects with stacking faults. Heterogeneous precipitation of the γ′ phase occurs specifically at the interfacial defects associated with dislocations. This preference arises from two factors: the easy emission of Shockley partial dislocations from these interfaces, which facilitate the formation of the γ′ structure, and elemental segregation, which creates a favourable chemical environment for γ′ precipitation. During the lengthening of γ′, its compositional transformation closely follows its structural transition due to the attraction of Gd and Zn atoms into the γ′ structure. The γ′ phase form as either variant I or II, depending on the extra half atomic plane of the associated dislocation is normal or parallel to the interface. This variant selection is influenced by the type of partial dislocations emitted from the interfacial defects. [Display omitted] [ABSTRACT FROM AUTHOR]

Previous work has shown that the shape memory effect (SME) exhibited a strong negative dependence on the density of annealing twin boundaries (ATBs) in Fe-Mn-Si-based alloys. Reducing the density of ATBs has thus been an effective way to improve the SME of Fe-Mn-Si-based alloys. This study investigated the effects of trace B doping on the density of ATBs and the resultant SME in solution-treated Fe-Mn-Si-based alloys. Results indicated that doping 89 ppm B effectively reduced the density of ATBs in the solution-treated Fe-Mn-Si-based alloy. Consequently, its SME was remarkably improved. The maximum shape recovery strain reached 2.7 % in the B-doped alloy, 1.3 % higher than in the alloy without B doping. This work demonstrates a new avenue to improve the SME by doping trace B, which is of significance for the fabrication of Fe-Mn-Si-based shape memory alloys in a more cost-effective manner. [Display omitted] • Effects of trace B doping on grain boundary characters and shape memory effect (SME) of Fe-Mn-Si-based alloys were studied. • Doping of 89 ppm B atoms effectively reduced the density of annealing twin boundaries (ATBs), thus improving SME. • B doping promoted both the thermal- and stress-induced ε martensitic transformation. • The segregation of B atoms at grain boundaries reduced the density of ATBs and slightly refined grain size. [ABSTRACT FROM AUTHOR]

Nanotwinned metals have exhibited many enhanced physical and mechanical properties. Twin boundaries have recently been introduced into sputtered Al alloys in spite of their high stacking fault energy. These twinned Al alloys possess unique microstructures composed of vertically aligned Σ3(112) incoherent twin boundaries (ITBs) and have demonstrated remarkable mechanical strengths and thermal stability. However, their strain rate sensitivity has not been fully assessed. A modified nanoindentation method has been employed here to accurately determine the strain rate sensitivity of nanotwinned Al–Zr alloys. The hardness of these alloys reaches 4.2 GPa while simultaneously exhibiting an improved strain rate sensitivity. The nanotwinned Al–Zr alloys have shown grain size-dependent strain rate sensitivity, consistent with previous findings in the literature. This work provides insight into a previously unstudied aspect of nanotwinned Al alloys. [ABSTRACT FROM AUTHOR]

In this study, the role of twin-twin interactions on the distributions of local defects (e.g., dislocations) and stress fields in a magnesium alloy is investigated. A co-zone (10 1 ¯ 2) - (1 ¯ 012) tensile twin junction in a deformed Mg-3wt.%Y alloy is analyzed using transmission electron microscopy (TEM). The results show that the morphology of the impinging (1 ¯ 012) twin is asymmetric, and the non-interacting boundary of the recipient (10 1 ¯ 2) twin is irregular. Detailed analysis of TEM images reveals that type-II pyramidal [ 1 ¯ 2 1 ¯ 3 ] (1 2 ¯ 12) dislocations concentrate in the vicinity of the twin-twin junction site. The same 〈c + a〉 dislocations are also observed inside the interacting twin domains along with a few 〈a〉 dislocations. The 〈c + a〉 dislocations emanating from the impinging (1 ¯ 012) twin boundary have edge character and are extended with faults parallel to the basal plane. In contrast, the 〈c + a〉 dislocations connected to the recipient (10 1 ¯ 2) twin are predominantly screw orientation and compact. Elasto-viscoplastic fast Fourier transform based crystal plasticity calculations are performed to rationalize the observed twin morphology and local dislocation distribution. The model calculations suggest that the local stress fields generated at the junction site where the two twins meet are responsible for the experimentally observed concentration of 〈c + a〉 dislocations. The calculated stress fields are asymmetric with respect to the junction site, explaining the observed asymmetric morphology of the impinging twin. Overall, these findings show strong effects of twin-twin interactions on the distribution of dislocations as well as the evolution of the twinned microstructure and as such, can help advance understanding of twinning in Mg alloys and their effect on mechanical behavior. [ABSTRACT FROM AUTHOR]

Short-range order (SRO) plays an important role in improving the mechanical properties of Mg alloys. In this study, we performed first-principle calculations to quantify the effects of SRO on solid solution strengthening (SSS) and grain boundary (GB) in Mg alloys. The SRO has a positive effect on decreasing the stacking fault (SF) energy. It is also identified that the SRO structure prefers to segregate in the twin boundaries (TB) than the SF due to lower segregation energies of the SRO on the TB than it is on the SF. In order to quantitatively correlate the SRO strengthening with the SSS, critical resolved shear stress (CRSS) is proposed based on the volume and chemical misfits. The newly formulated strengthening model predicts the tensile strength of binary Mg–Y alloy accurately, proving that the ab initio calculations can evaluate alloy properties quantitatively from atomistic scale. [ABSTRACT FROM AUTHOR]

For the sake of comprehending the mechanical mechanisms of nano‐twinned (NT) Cu–Ag alloys with grain boundary affect zone (GBAZ) segregation, molecular dynamics (MD) simulations were used to observe its behaviours during the nano‐indentation progress. The effect of grain size, alloying atoms (Ag) content as well as twin boundary spacing (TBS) on the deformation behaviours are considered in this investigation. The open visualization tool OVITO is used to directly observe the deformation progress of nanocrystals during nano‐indentation. The reaction between lattice dislocations and twin boundaries is recorded and analyzed in detail as the indentation deepens. The simulation results demonstrate a positive correlation between the twin boundary spacing and the occurrence of dislocations. The dislocation rings will appear more effortlessly as the TBSs increase. Meanwhile, it is frequently observed that the face centre cubic (FCC) atoms are transformed into body centre cubic (BCC) atoms. This work will help to seek for novel metal materials with high strength, high ductility and great electrical conductivity. [ABSTRACT FROM AUTHOR]

Electron backscatter diffraction (EBSD) coupled with in-situ tensile loading is powerful for investigating the microstructural evolution of alloys. Thermo-mechanically treated f.c.c. medium-entropy alloys (MEAs) typically have high densities of annealing twin boundaries (ATBs), which can not only strengthen but also toughen the MEA via interacting with dislocations. However, the evolution of ATBs and other substructures in plastically-deformed MEA has not yet been revealed. Plastic deformation involving dislocation evolution, active slip systems, lattice rotation, boundary transformation, and grain subdivision in a polycrystalline MEA Ni 41.4 Co 23.3 Cr 23.3 Al 3 Ti 3 V 6 was studied using in-situ EBSD. The slip was accompanied by heterogeneous lattice rotation among grains and within grains, where inhomogeneous plasticity was accommodated by geometrically-necessary dislocations (GNDs). Both GND and low-angled boundaries (LABs) densities substantially increased with progressive strain, which was mainly concentrated in sites approaching ATBs or grain boundaries (GBs). Located stress, lattice rotation, or curvature caused a loss in the coherence of ATBs, which resulted in integrity loss with increasing strain and promoted a decrease in density by 60 %. Further, lattice rotation incompatibility due to constraints from neighboring grains leads to grain fragmentation into various misorientated volumes, which were separated by LABs or high-angle boundaries (HABs). The grain orientation angle increased with progressive strain and crystallographic 〈111〉 orientation gradually spread toward a tensile direction. Slip systems with maximum Schmid factor were activated first at ε ≥ 3.9 %, which is almost the same with experimental slip traces. Both single slip and double slip occurred during plasticity, where straight slip traces tend to curve due to lattice curvature. Slip transfers are not only controlled by geometric compatibility factor, which can occur between some neighboring grains with low geometric compatibility factor but high Schmid factor. • Increased dislocations were mainly concentrated near ATBs or GBs owing to pile-ups by those planar obstacles. • Lattice rotation and located stress are responsible for annealing twin boundary degradation with progressive strain. • Lattice rotation incompatibility due to constraints from neighboring grains leads to grain fragmentation separated by HABs. • Grain orientation angle increased with progressive strain and < 111> orientation gradually spread toward tensile direction. • Slip transfer between adjacent grains is controlled by geometric compatibility factor or high Schmid factor. [ABSTRACT FROM AUTHOR]

Incoloy825 alloy is a Ni–Fe–Cr corrosion resistant alloy, which is widely used in oil and gas pipelines, heat exchangers, chemical plants and boiler pipelines. In the application environment of high-temperature and high-pressure sulfur-containing and chlorine containing steam pipelines, the pipeline surface is easy to deposit salt film, resulting in high-temperature hot corrosion, which requires the alloy to have excellent sulfur and chlorine corrosion resistance. The hot corrosion behavior of Incoloy825 alloy was investigated by using Na2SO4 + NaCl molten salt at 950 °C. The results show that the hot corrosion products mainly include (Cr,Fe)2O3, NiO, NiCr2O4, FeCr2O4, NiFe2O4 and (Fe,Ni)S2. Sulfur and chlorine elements in molten salt act as catalysts in vulcanization and chlorination reactions. The hot corrosion path penetrates along the random high-angle grain boundary, and the special grain boundary can block the penetration path of hot corrosion. Chromium mainly precipitates along the random high-angle grain boundary. The special grain boundary can inhibit the precipitation of chromium, so as to reduce the combination probability of sulfur and chlorine with chromium. Σ11 boundary, Σ5 boundary and incoherent Σ3 twin boundary do not block the corrosion path, and coherent Σ3 twin boundary plays a key role in blocking the corrosion path. For alloys with low stacking fault energy, taking advantage of the characteristics that their microstructure contains a large number of annealing twins, increasing the proportion of special grain boundaries is an effective means to improve their hot corrosion resistance. [ABSTRACT FROM AUTHOR]

CoCrNi medium-entropy alloy has superior cryogenic properties with simultaneous growth of strength and plasticity at low temperatures. In order to observe the microstructure and deformation behavior of the alloy at the atomic scale, its mechanical properties and deformation mechanism at different temperatures and strain rates were investigated using molecular dynamics. It is indicated that the alloy's strength was enhanced at low temperatures and high strain rates due to the production of high dislocation density. The introduction of grain boundaries significantly decreased the dislocation density during the alloy's deformation and correspondingly reduced the crystal strength. However, the introduction of twin boundaries in polycrystalline grains obviously enhanced the strength of the polycrystal, especially at the twin boundary spacing of 3.08 nm. The strength's enhancement was attributed to the increasing dislocation density produced by the interaction between twin boundaries and dislocations during deformation. [ABSTRACT FROM AUTHOR]

Two different types of shear bands generate in ultrafine-grained (UFG) CoCrFeMnNi high-entropy alloys deformed at 77 K, i.e. commonly-observed low angle grain boundary (LAGB) type and unusual twin-coupled type. Twin-coupled shear bands exhibit a misorientation of 56–67° with the matrix, in contrast to the LAGB shear band with a misorientation of 6–12°. Both annealing twins and deformation twins can act as precursor for twin-coupled shear bands, where dislocation accumulation along twin boundaries can tune the orientation of twin lamella. These observations suggest that twin-coupled shear bands can act as an important plastic carrier in materials deformed under extreme conditions. Atomic structure of twin-coupled shear band is unveiled in an UFG CoCrFeMnNi HEA deformed at 77 K, which involves in dislocation-twin boundary coupled mechanism, based on delicate structural characterization via high resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Bi2Te3 based thermoelectric alloys have been commercialized in solid-state refrigeration, but the poor mechanical properties restrict their further application. Nanotwins have been theoretically proven to effectively strengthen these alloys and could be sometimes constructed by strong deformation during synthesis. However, the obscure underlying formation mechanism restricts the feasibility of twin boundary engineering on Bi2Te3 based materials. Herein, thorough microstructure characterizations are employed on a series of Bi0.4Sb1.6Te3+δ alloys to systematically investigate the twins' formation mechanism. The results show that the twins belong to the annealing type formed in the sintering process, which is sensitive to Te deficiency, rather than the deformation one. The Te deficiency combined with mechanical deformation is prerequisite for constructing dense nanotwins. By reducing the δ below -0.01 and undergoing strong deformation, samples with a high density of nanotwins are obtained and exhibit an ultrahigh compressive strength over 250 MPa, nearly twice as strong as the previous record reported in hierarchical nanostructured (Bi, Sb)2Te3 alloy. Moreover, benefitting from the suppressed intrinsic excitation, the average zT value of this robust material could reach near 1.1 within 30-250 °C. This work opens a new pathway to design high-performance and mechanically stable Bi2Te3 based alloys for miniature device development. [ABSTRACT FROM AUTHOR]

An obvious strengthening phenomenon has been observed in the Mg-6Al-1Zn (AZ61) alloy after simultaneous loading and aging at 170 °C. Being different to aging after pre-strain, the simultaneous loading and aging can obviously increase the yield stress of the alloy. Microstructural analysis shows that a larger quantity of the Al12Mg17 can be obtained by simultaneous loading and aging in a relatively short aging time, compared with aging after pre-strain. It is speculated that the loading during aging is more beneficial for nucleation of the precipitates. In the same aging time, it is found that the sample subjected to simultaneous loading and aging shows a higher yield stress than the sample aged after pre-strain. To extend aging time, a large quantity of Al12Mg17 can be obtained in the pre-strained sample. However, it is demonstrated that the yield stress of the sample subjected to aging after pre-strain is lower than that of the sample subjected to simultaneous loading and aging, despite these two samples containing the same quantity of precipitates. It is speculated that the occurrence of the precipitates plays a role in preventing dislocation gliding and twin expanding, thus leading to a strengthening effect. Additionally, atoms segregated in twin boundaries may partly strengthen the material. It is found that a large quantity of precipitates can be obtained in a relatively short aging time by using the simultaneous loading and aging, reducing the softening effect caused by aging. The observed phenomenon may provide a new strategy for strengthening magnesium alloys. [ABSTRACT FROM AUTHOR]

Twinning is a critical deformation mode in Mg alloys. Understanding deformation twinning (DT) is essential to improving mechanical properties of Mg alloys. To address the experimentally observed conspicuous hardening effects in Mg-1.8Zn-0.2Ca alloys, interactions between the {10–12} twin boundaries (TBs) and solute clusters in Mg-Zn-Ca alloys were examined via molecular dynamics (MD) simulations. We find that the Zn/Ca-containing clusters show different hindering effects on TBs and an increment in the applied shear stress of 100 MPa is required to accomplish the interaction between the boundary and the cluster with Ca content > 50 at%. The cluster hardening effects on twinning are positively correlated to the Ca content and the size of the clusters in Mg-Zn-Ca alloys. [ABSTRACT FROM AUTHOR]

The influence mechanism of twin boundary in Ni–Co alloys is responsible for their deformation and technological applications. Herein, the uniaxial tensile loading of the Ni–Co single crystal nanopillars with twin boundaries is carried out by simulation. When the number of twin boundaries exceeds two layers, the effect of twinning boundary on dislocation is obvious, and the migration and reaction of twin boundaries lead to an increase in the number of dislocations accommodated inside, which is conducive to increasing the strength of the nanopillars. At low temperature, the dislocations are easy to penetrate and expand the twin grain boundary, while at high temperature, due to the aggravation of thermal motion, the resulting dislocations decrease. Meantime, the reaction between dislocations and twin boundaries leads to the disappearance of some original twin grain boundaries. As the strain rate increases, the main deformation mode of the nanopillar changes from the reaction of dislocation and twin boundary to twin boundaries migration. When the volume ratio of grain boundary void is less than 2.3%, the plastic deformation fluctuation is relatively stable. Nevertheless, when the volume ratio is greater than or equal to 2.3%, the fluctuation of the plastic deformation stage decreases rapidly. [ABSTRACT FROM AUTHOR]