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It is of great academic significance to understand the influence that the atomic-scale structure of interfaces and boundaries within materials has on magnetic coupling characteristics and promote the innovation of advanced magnetic devices. Here, we carried out a systematic investigation of the atomic and electronic structures of twin boundaries (TBs) in Li0.5Fe2.5O4 (LFO) thin films and determined their concurrent magnetic couplings using atomic-resolution transmission electron microscopy and first-principle calculations at the atomic scale. The results show that ferromagnetic or antiferromagnetic coupling can exist across the different TBs in LFO thin films, and electrical structures within a few atomic layers directly rely on the atom arrangement across the TB. Uncovering one-to-one relationships between the magnetic coupling properties of individual TBs and atomic-scale structures can clarify a thorough comprehension of numerous fascinating magnetic properties of commonly utilized magnetic materials, which will undoubtedly encourage the progress of sophisticated magnetic materials and devices. [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]

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]

In situ transmission electron microscopy was used to observe the electromigration-driven sliding behavior of twinned face-centered cubic-Co fillers sliding inside multi-walled carbon nanotubes with an inner-diameter step. Each filler contained a twin boundary located at the nanotube inner-diameter step. Under application of an electric current, the twinned Co fillers moved across the steps and changed their diameter, and the position of the twin boundary was maintained at the nanotube inner-diameter step. [ABSTRACT FROM AUTHOR]

A growing number of superconducting materials display evidence for spontaneous time-reversal symmetry breaking (TRSB) below their critical transition temperatures. Precisely what this implies for the nature of the superconducting ground state of such materials, however, is often not straightforward to infer. We review the experimental status and survey different theoretical mechanisms for the generation of TRSB in superconductors. In cases where a TRSB complex combination of two superconducting order parameter components is realized, defects, dislocations and sample edges may generate superflow patterns that can be picked up by magnetic probes. However, even single-component condensates that do not break time-reversal symmetry in their pure bulk phases can also support signatures of magnetism inside the superconducting state. This includes, for example, the generation of localized orbital current patterns or spin- polarization near atomic-scale impurities, twin boundaries and other defects. Signals of TRSB may also arise from a superconductivity-enhanced Ruderman- Kittel-Kasuya-Yosida exchange coupling between magnetic impurity moments present in the normal state. We discuss the relevance of these different mechanisms for TRSB in light of recent experiments on superconducting materials of current interest. [ABSTRACT FROM AUTHOR]

The present study investigated the dissolution and oxidation corrosion behaviors of Hastelloy exposed to static liquid lead‐bismuth eutectic (LBE) at 500°C with an oxygen concentration of 1 × 10−6 mass%. Hastelloy exhibited better LBE corrosion resistance than the Monel alloy. Both dissolution and oxidation corrosion were observed in Hastelloy, and the maximum LBE penetration depth and spinel layer thickness in the corroded sample after 4000 h of exposure reached 120 ± 36 and 21 ± 12 µm, respectively. Annealing twin boundaries provided favorable paths of accelerated LBE penetration into the matrix, resulting in selective leaching of Ni. Microstructural characterization revealed that the spinel layer formed between penetrated LBE and base metal slowed down the elemental interdiffusion, thereby retarding the dissolution rate. Volumetric changes induced by LBE penetration promoted the formation of stacking faults and dislocations, which could provide more channels for elemental diffusion, leading to the propagation of dissolution attack. [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]

The coarse β-grain structures typically found in titanium alloys like Ti–6Al–4V (wt pct, Ti64) and Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242), produced by high deposition rate additive manufacturing (AM) processes, are detrimental to mechanical performance. Certain modified processing conditions have been shown to lead to a more refined grain structure, which has generally been attributed to a change in the solidification conditions with respect to the experimental Hunt diagram proposed by Semiatin and Kobryn. It is shown that with Wire Arc AM (WAAM) increasing the wire feed speed (WFS) is effective in promoting a columnar-equiaxed transition (CET). Conversely, estimates of the dendrite-tip undercooling using the KGT model suggest that this will be too small for free nucleation without the addition of artificial nucleants, due to the very low solute partitioning in Ti alloys. It is also shown that it is difficult to promote a CET with plasma transferred arc WAAM as computational fluid dynamics (CFD) melt-pool simulations indicate that the solidification parameters remain within the columnar region on the Semiatin-Kobryn Hunt map, within the constraints of a stable process. However, a high fraction of twin boundaries was observed in the refined β-grain structures seen at high WFS. This has been attributed to departure of 001 β alignment from the direction of maximum thermal gradient, caused by the curvature of the fusion boundary, stimulating dendrite twinning during solidification. In addition, it is shown that increasing the WFS leads to a change in melt-pool geometry and a reduction of remelt depth, which promoted dendrite twinning and grain refinement. [ABSTRACT FROM AUTHOR]

Fe–Mn–Cr–N austenitic stainless steel is widely used in engineering fields because of its good ductility, but its relatively low yield strength limits its application range. In this study, Fe–Mn–Cr–N steel was fabricated with different parameters by friction stir processing (FSP). To explain the effect of the rotation rate and feed speed on the microstructure evolution and mechanical properties of Fe–Mn–Cr–N steel, four sets of parameters were selected. The numerical simulation results reveal that the maximum temperature and strain at the tool-workpiece interface on the advancing side (AS) are 948.8 °C and 39.3 mm/mm, respectively. Under the action of severe strain and frictional heat production during processing, the original coarse columnar grains were refined into uniform equiaxed grains with an average grain size of approximately 10 μm in the stir zone (SZ). Moreover, under the experimental conditions, the δ-ferrites gradually transformed into austenite, and all the δ-ferrites disappeared in the SZ with the greatest strain. In addition, a large number of Σ3 twins formed in this region. Consequently, microstructure refinement is dominated by dynamic recrystallization (DRX), while nucleation is accelerated by dissolution and spheroidization of δ ferrites and evolution of Σ3 twin boundaries. The Fe–Mn–Cr–N steel fabricated at 600 rpm-50 mm/min had the best comprehensive mechanical properties, i.e., its YS, UTS and El changed to 400.9, 649.0 MPa and 60.7 pct from 211.4, 421.2 MPa and 62.4 pct of the original as-casted Fe–Mn–Cr–N steel, respectively. The improvement in the YS was mainly attributed to solution strengthening (σSS = 114.4 MPa) and boundary strengthening (σGB = 189.5–238.1 MPa). [ABSTRACT FROM AUTHOR]

We setup a dislocation dynamics finite element framework by bridging a dislocation dynamics program and an open source finite element program. As part of initial verification, deformation of single crystal micro-pillar having single and double glide activation is demonstrated. A case study of a twin boundary is presented wherein the dislocation pile-up at the grain boundary and formation of a residual dislocation are shown. For studying the dislocation interactions with other grain boundaries, model grain boundaries are considered. We consider three synthetic grain boundaries namely transparent, semi-transparent, and impenetrable. The model's transparent and semi-transparent grain boundaries contain no dislocations and very low density of dislocations in them, respectively, and thus low number of interactions with other dislocations. More junctions and cross-slip occurrences are recorded near the semi-transparent grain boundary. The most dislocation–dislocation interactions near grain boundaries result into glissile junctions. The current results are compared against literature data and it is observed that other than junction formation, cross-slip is very frequency observed near grain boundaries. [ABSTRACT FROM AUTHOR]

The effect of grain boundary retardation by annealing twins in pure copper has been experimentally and theoretically investigated. A model that describes the influence of annealing twins on the migration of grain boundaries in pure metals has been proposed. The retarding force from the twins has been demonstrated to be analogous to the Zener retarding force created by incoherent fine particles. An equation has been derived to calculate the retarding force induced by annealing twins. The force has been demonstrated to be inversely proportional to the size of the twins and directly proportional to their volume fraction. The simulation results have been compared with the experimental results. A satisfactory correlation between the theoretical and experimental results has been achieved. [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]

Twin boundary (TB) strengthening in nanotwinned metals experiences a breakdown below a critical spacing at which softening takes over. Here, we survey a range of nanotwinned materials that possess different stacking fault energies (SFEs) and understand the TB strengthening limit using atomistic simulations. Distinct from Cu and Al, the nanotwinned, ultralow SFE materials (Co, NiCoCr, and NiCoCrFeMn) intriguingly exhibit a continuous strengthening down to a twin thickness of 0.63 nm. Examining dislocation slip mode and deformation microstructure, we find the hard dislocation modes persist even when reducing the twin boundary spacing to a nanometer regime. Meanwhile, the soft dislocation mode, which causes detwinning in Cu and Al, results in phase transformation and lamellar structure formation in Co, NiCoCr, and NiCoCrFeMn. This study, providing an enhanced understanding of dislocation mechanism in nanotwinned materials, demonstrates the potential for controlling mechanical behavior and ultimate strength with broadly tunable composition and SFE, especially in multi-principal element alloys. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive first-principles density functional theory (DFT) study of solute segregation at { 10 1 ¯ 1 } and { 10 1 ¯ 2 } twin boundaries (TBs) in Mg. A total of 56 solute elements were investigated. For each solute element, the preferential segregation sites at two TBs were identified and the associated segregation energies were computed. A two-factor model that considers both lattice strain and electronegativity, representing the mechanical and chemical effects respectively, has been proposed to predict the solute segregation energy. The model prediction shows good agreement with the DFT calculation. It was found that the mechanical effect dominates the solute segregation energy. However, depending on the site of segregation, the chemical effect can become sizable to warrant consideration. The degree of solute segregation at TBs at different temperatures was then quantified by calculating the solute concentration at TBs at different temperatures. The effect of solutes in either strengthening or weakening the TB was also evaluated. The results provide a basis for selecting promising solutes in the development of new high-performance Mg alloys. [ABSTRACT FROM AUTHOR]

Twin and dislocation have critical influence on the mechanical properties of the widely used AZ80 magnesium alloy. In the present work, we designed room temperature multi-direction forging (MDF) at different strain amplitudes (3% and 6%) with a same strain, introduced twin and dislocation structures and improved the mechanical properties of the alloy. The results showed that the material reached the limit of deformation with a cumulative strain of 0.72. With the increase of strain, the grain size decreased and the dislocation density increased gradually. At low strain amplitude, the transformation of dislocations at twin boundaries (TBs) caused twinning expansion and detwinning. While at high strain amplitude, interactive twin structure hindered the over-expansion of twins. In addition, high-density dislocations accumulate at the twin boundaries, which stimulates the nucleation of twin variants and further refines the grains. In the process of plastic deformation, dislocation strengthening contributed the main yield strength, and fine twins provided a certain level of hardening ability. Through the interaction between the dislocations and twins, the strength and plasticity of the material were synergistically improved, and excellent mechanical properties with ultimate tensile strength of 486 MPa, yield strength of 385 MPa, and elongation of 8.1% were finally obtained.

Rapid-thermal annealing (RTA) of InSb precursor films, deposited by sputtering using an Ar plasma at room temperature, has been investigated to achieve high carrier mobility on low-cost glass substrates. Although InSb films containing residual Ar (∼1%) were partially lost by evaporation during RTA, such evaporation during RTA is suppressed by reducing the residual Ar to ∼0.3%. The crystallinity of the films is significantly increased by RTA at temperatures above 400 °C. The electron mobilities of the films increase with increasing RTA temperature up to 490 °C, showing the maximum values (9000–10 000 cm2 V−1 s−1) at 490 °C, and then, the mobilities decrease at RTA temperatures above 490 °C. The mobilities of 9000–10 000 cm2 V−1 s−1 are obtained for films with a wide range of thickness (300–1000 nm) grown at 490 °C. Detailed analysis indicated that the high carrier mobilities are realized by preferentially (111)-oriented large crystal domains (diameter: >100 μm), obtained by the regrowth of randomly oriented small grains, together with a low barrier height (16 meV) at the sub-domain boundaries (twin boundaries) in the large domains. The RTA after the sputtering technique will facilitate high-performance InSb-based devices with low production costs. [ABSTRACT FROM AUTHOR]

Nanotwined (nt) copper is attractive in applications such as microbumps in the microelectronics industry because nt-copper presents sound mechanical and physical properties. To date, most studies of the mechanical properties of nt-copper have been performed at macroscales. However, different stories are told at micro/nanoscales, e.g., smaller size leads to higher strength. Understanding the mechanical properties of nt-copper at micro/nanoscales is crucial for improving the reliability and endurability of microdevices. In this paper, we fabricated nt-copper film with tailored microstructures, i.e., twin boundaries (TBs) with different spacings and orientations (parallel or slanted to loading direction). Then, we applied micro-compression testing, atomistic simulation, and theoretical analysis to investigate the influence of vertical twin-boundary spacing λ and orientation on the deformation behavior of nt-micropillars. Results show that the yield stress is increased with decreasing vertical λ. Micropillars with slanted λ = 15.5 nm TBs present the greatest strength, which may be attributed to a finer λ. The phenomenon, strength increasing with decreasing λ, was well explained by the Hall–Petch and confined layer slip models. Large-scale molecular dynamics simulations were used to uncover the atomistic and real-time deformation mechanisms. This microscale research on nt-micropillars may provide insights on designing advanced microelectronics. [ABSTRACT FROM AUTHOR]

The crystal structure and transformation path from austenite to 10M martensite in Ni–Mn–Ga single crystal are examined employing high‐energy synchrotron radiation, scanning, and transmission electron microscopy. Using temperature gradient, an austenite/twinned martensite interface is stabilized revealing the crystal structure and microstructure of both phases and the transformation sequence across the interface. Depending on the distance from the interface, three distinct types of martensite crystal lattice, namely simple tetragonal and two monoclinic modulated ones, that is, 10M′ and 10M are confirmed. In situ measurements show that lattice mismatch formed at the habit plane is compensated by the formation of micro‐twinned and branched martensite along with an elastic change in lattice parameters. It is shown that the characteristics for periodic shuffling twin boundaries, such as modulation twins or inverted stacking faults, are installed in later stages of transformation. In other words, large microstructure elements that most efficiently accommodate the strain are installed first, and then smaller elements are operable. Overall, the experimental results show that the crystal lattice does not adapt modulated phase at the habit plane and cannot be built up from simple non‐modulated tetragonal blocks but rather a specific sequence of phase transformations using shear/shuffling deformation takes place. [ABSTRACT FROM AUTHOR]

Commercial oxygen-free copper sheets were cold-rolled with reduction rates ranging from 20% to 87% and annealed at 400, 500 and 600 °C. The microstructure and texture evolution during the cold-rolling and annealing processes were studied using optical microscopy (OM), scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). The results show that the deformation textures of {123}<634> (S), {112}<111> (Copper) and {110}<112> (Brass) were continuously enhanced with the increase in cold-rolling reduction. The orientations along the α-oriented fiber converged towards Brass, and the orientation density of β fiber obviously increased when the rolling reduction exceeded 60%. The recrystallization texture was significantly affected by the cold-rolling reduction. After 60% cold-rolling reduction, Copper and S texture components gradually decreased, and the {011}<511> recrystallization texture component formed with the increase in annealing temperature. After 87% cold-rolling reduction, a strong Cube texture formed, and other textures were inhibited with the increase in annealing temperature. The strong Brass and S deformation texture was conducive to the formation of a strong Cube annealing texture. The density of the annealing twin boundary decreased with the increase in annealing temperature, and more annealing twin boundaries formed in the oxygen-free copper sheets with the increase in cold-rolling reduction. [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]

The manufacturing process for wrought Ti alloys with the hexagonal close-packed (HCP) structure introduces a complicated microstructure with abundant intra- and inter-grain boundaries, which greatly influence performance. In the hexagonal close-packed (HCP) structure, two types of grain boundaries are commonly observed between grains with ~90° misorientation: the basal/prismatic boundary (BPB) and the coherent twin boundary (CTB). The mechanical response of the BPB and CTB under external loading was studied through molecular dynamic simulations of HCP-Ti. The results revealed that CTB undergoes transformation into BPB through the accumulation of twin boundary (TB) steps and subsequent emission of Shockley partial dislocations. When the total mismatch vector is close to the Burgers vector of a Shockley partial dislocation, BPB emits partial dislocations and further grows along the stacking faults. When a pair of CTBs are close to each other, severe boundary distortion occurs, facilitating the emission and absorption of partial dislocations, which further assists the CTB-BPB transformation. The present results thus help to explain the frequent observation of coexisting CTB and BPB in HCP alloys and further contribute to the understanding of their microstructure and property regulation. [ABSTRACT FROM AUTHOR]

The synergic effects of scanning pattern types and subsequent heat treatment on the room- and elevated-temperature tensile properties of powder bed fusion-laser beam additively manufactured Hastelloy X Ni-based superalloy are investigated. The samples were built via bi-directional and chessboard scanning patterns. The as-built microstructures comprised dislocation and solidification cells embedded within the columnar grains. After applying heat treatment at 1175 °C for various soaking times, the as-built microstructures were gradually modified via recrystallization resulting from the residual stresses. The recrystallization kinetics equations for both bi-directional and chessboard samples were derived. It was found that the recrystallization occurred via the twinning-assisted nucleation mechanism and was promoted through bulging. The chessboard and bi-directional samples had similar driving forces; however, the recrystallization fraction in the chessboard sample was higher than that of the bi-directional sample due to differences in the grain's micro-texture. It was observed that the heat treatment cycle had no significant influence on the room- and high-temperature strength; by contrast, it interestingly improved the room- and high-temperature ductility due to reduced dislocation density and formation of twin boundaries. In addition, the heat-treated chessboard sample displayed superior hot tensile ductility than the bi-directional ones, owing to more promotion in recrystallization. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations, we study the roles of geometry, boundary conditions, and nanotwinned structure on the mechanical response of Cu ⟨ 110 ⟩ cylindrical nanopillars under tensile loading. Specifically, we investigate the stress–strain responses, deformation mechanisms, and defect evolution in nanopillars of varying height-to-diameter ( H / D ) ratios, capped with rigid layers to resemble hard coatings, and with microstructures consisting of columnar grains with and without nanoscale coherent twin boundaries (CTBs). Our results indicate that the disk-shaped nanopillars (DPs) with low H / D ratios exhibit high yield strength, significant triaxial tension stress, and pronounced plastic deformation. This deformation is accompanied by high defect density near the Cu/rigid layer interfaces, driven by dislocation pile up from multiple activated slip systems. Conversely, the deformed rod-shaped nanopillars of large ratios exhibit localized plastic deformation characterized by necking phenomena. Our results reveal the dominant role of Shockley type dislocations in plastic deformation, particularly in DPs, which display higher dislocation densities due to reduced dislocation annihilation events at free surfaces and pile up at interfaces. Notably, deformed DPs exhibit a unique vacancy-induced nanovoid nucleation mechanism at interfaces, resulting from the coalescence of vacancies generated during shearing of jogs. Additionally, the results demonstrate that dislocations glide between CTBs forming wide stacking faults, or traverse CTBs in a zigzag pattern as perfect dislocations, confirming a recently hypothesized cross-slip-like transmission in a recent experimental observation. Our simulations indicate that nanometer-spaced CTBs in Cu ⟨ 110 ⟩ nanopillars act as weak barriers to dislocation motion during tensile loading, leading to only a marginal enhancement of mechanical properties. [ABSTRACT FROM AUTHOR]

Comprehending the mechanical response of materials on an atomic level is pivotal in the optimisation of advanced materials with superior mechanical properties. This research article utilises the atomistic-scale based molecular dynamics simulations to report the uniaxial tensile behaviour of bicrystalline Ni-6Cu (Nickel – 94% and Copper – 6%) alloy incorporated with pre-existing faceted Σ3 [111] 60° {11 8 5} grain boundaries. The primary aim of this investigation is to comprehend the performance of bicrystalline Ni-6Cu alloy under varying thermodynamic conditions and to assess the influence of pre-existing faceted grain boundaries on its tensile behaviour. This work encompasses a range of strain rates (108 to 1010 1/s) and temperatures (spanning from 100 to 900 K) for the uniaxial tensile deformation simulations. The outcomes unveil that the Young's modulus of Ni-6Cu alloy (with pre-existing faceted grain boundaries embedded in its domain) was inversely proportional to temperature and constant with respect to strain rate. For the same configuration, yield stress was inversely and directly proportional to temperature and strain rate, respectively. Interestingly, incipient plasticity in the tensile stress–strain response was observed at lower temperature and lower strain rate. From the microstructural point of view, at lower temperatures, the incoherent twin boundary served as a source for the nucleation of stacking faults; however, as the temperature increased, both the incoherent twin boundary and the tips of coherent twin boundary function as the source for stacking faults formation. Our simulations also verified the GB's anti-thermal (or non-Arrhenius) migration behaviour even under tensile load. [ABSTRACT FROM AUTHOR]

This paper provided an effective method to further improve the mechanical properties of the AZ80+0.4%Ce magnesium alloy wheel spoke. The effect of high strength and ductility was obtained with a yield strength of 295.36 MPa, an elongation of 10%, by the combination of pre-deformation (7% deformation) and two-stage aging treatment (120 °C/9 h + 175 °C/24 h). The evolution of the microstructure and properties of the alloy was explored under the coupling conditions of different pre-deformation degrees and multi-stage aging. The results show that, pre-deformation introduced a large number of (10 1 ¯ 2) tensile twinning and dislocations, which greatly promoted the probability of continuous precipitates (CPs) appearing. On the contrary, the discontinuous precipitates (DPs) were limited by the vertical and horizontal twin structure. As a result, the pre-nucleation method of two-stage aging increased the proportion of CPs by 34%-38%. Owing to the DPs was effectively suppressed, the alloy's yield strength has been greatly improved. Besides, under multi-stage aging, the twin boundaries induce protruding nucleation to form static recrystallization by hindering the migration of dislocations, and the matrix swallows the twins, then the texture gradually tilts from the two poles to the basal plane. As an important supplement, the grain refinement and oblique texture promoted the improvement of the yield strength of the component. [ABSTRACT FROM AUTHOR]

Serrated flow phenomenon has been widely observed among different metals due to the potential influence on their applications. Uniaxial tensile tests of nickel-based superalloy GH536 were carried out at loading rates of 0.06, 0.60, 3.60, and 36.00 mm·min−1 at room temperature, respectively. The tensile stress–strain curves demonstrate repetitive and discontinuous yielding behavior, namely serrated flow. It is observed that the stress–strain curves were dominated by type B serration, and original annealing twin boundaries (TBs) were distorted to various degrees under comparatively different lower tensile rates. In contrast, the TBs almost disappear, and the type B serrations become smoother and regular under the higher loading rates. This phenomenon can be attributed to the interactions between TBs and dislocations during tensile deformation. Coupled effects of the mobile and immobile dislocations illustrate the unsteady amplitude of serrations observed in stress–strain curves. Transmission electron microscope images of tested pieces reveal the interaction of dislocation and TB, with dislocation tangling around the TBs. [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]

One-unit-cell FeSe films on SrTiO3 substrates are of great interest owing to significantly enlarged pairing gaps characterized by two coherence peaks at ±10 meV and ±20 meV. In-situ transport measurement is desired to reveal novel properties. Here, we performed in-situ microscale electrical transport and combined scanning tunneling microscopy measurements on continuous one-unit-cell FeSe films with twin boundaries. We observed two spatially coexisting superconducting phases in domains and on boundaries, characterized by distinct superconducting gaps ( Δ 1 ~15 meV vs. Δ 2 ~10 meV) and pairing temperatures (Tp1~52.0 K vs. Tp2~37.3 K), and correspondingly two-step nonlinear V ~ I α behavior but a concurrent Berezinskii–Kosterlitz–Thouless (BKT)-like transition occurring at T BKT ~28.7 K. Moreover, the onset transition temperature T c onset ~54 K and zero-resistivity temperature T c zero ~31 K are consistent with Tp1 and T BKT , respectively. Our results indicate the broadened superconducting transition in FeSe/SrTiO3 is related to intrinsic electronic inhomogeneity due to distinct two-gap features and phase fluctuations of two-dimensional superconductivity. The authors study monolayer FeSe via scanning tunneling microscopy and simultaneous micron-scale-probe-based transport. They observe distinct superconducting phases in domains and on boundaries between domains, with different superconducting gaps and pairing temperatures. [ABSTRACT FROM AUTHOR]

Defective rock-salt (R) Ti1-xO → rutile (r) TiO2-x transformation twinning occurred in a thin film with preferred shape and crystallographic orientation when deposited on silica glass substrates, with or without a coating of fluorine-doped tin oxide, using pulsed laser ablation of a rutile polycrystal under specific pulse energies in the range of 200 to 800 mJ per pulse in vacuum. The films were characterized by X-ray diffraction and electron microscopy and shown to contain nanocrystallites of R, r, and minor hightemperature- stabilized hexagonal Ti1-xO all with preferred orientations adopted by close-packed planes. The R + r intimate intergrowth was found to form a butterfly twin following the optimum crystallographic orientation relationship [101]R//[111]r with close-packed (111)R and (011)r planes as the twin boundary and phase interface with a fair 2-D coincidence site lattice in accordance with the dense (111)R-specific R → r transformation route. The R + r predominant film with aliovalent point defects and paracrystalline distribution of defect clusters showed characteristic white light absorbance, violet + green double emission, and fine photoelectron chemical properties for potential photovoltaic, photocatalytic, and optoelectronic applications, in particular for multiple temperature- and oxygen-fugacity sensors in terms of the R → r transformation. [ABSTRACT FROM AUTHOR]

Grain boundary diffusion in severely plastically deformed (SPD) CoCrFeMnNi high entropy alloy (HEA) has been studied by applying the tracer diffusion technique. After two passes of equal channel angular pressing (ECAP), three untra-fast diffusion paths in ECAP-processed CoCrFeMnNi HEA were distinguished, which were identified with twin boundaries, high-angle grain boundaries and porosity defects. The enhanced diffusivity is induced by a high strain localization in the vicinity of interfaces in a deformation-induced non-equilibrium state that is correlated with the pronounced deformation twinning due to the low stacking fault energy of the material. [ABSTRACT FROM AUTHOR]

A fundamental understanding of the morphological stability and microstructural characteristics of gold nanoparticles (Au NPs) is crucial for their diverse applications. In this study, spiky Au NPs are prepared by a seed‐mediated approach using citrate‐capped Au nanospheres as seeds. The morphological and microstructural characteristics of the spiky Au NPs are studied using 3D tomography transmission electron microscopy (TEM) analysis. Twin boundaries in all spikes of the Au NPs are identified by straight lines in the TEM images and specific crystallographic orientations. In addition, the analysis reveals that a careful approach is required when evaluating the morphological characteristics of spiky Au NPs using 2D images. A series of spiky Au NPs with sizes ranging from 62 to 323 nm is prepared by precisely controlling the amount of seed solution and first growth solution added during seed‐mediated growth. To elucidate the morphological and microstructural characteristics of the spiky Au NPs, a mechanism for the formation and evolution of the spikes is proposed based on the TEM results. [ABSTRACT FROM AUTHOR]

In the two-phase crystal EuRbFe4As4/EuFe2As2 (1144/122), a linear ordering of Abrikosov vortices, uncharacteristic for superconducting pnictides, has been found using the method of decorating with magnetic nanoparticles. The observed chains of vortices directed along crystallographic 〈110〉 axes of the orthorhombic EuFe2As2 phase are explained by pinning of vortices in the superconducting phase 1144 on linear defects associated with the twin boundaries of the non-superconducting 122 phase. [ABSTRACT FROM AUTHOR]

Tensile-compression fatigue deformation tests were conducted on AZ31 magnesium alloy at room temperature. Electron backscatter diffraction (EBSD) scanning electron microscopy was used to scan the microstructure near the fatigue fracture surface. It was found that lamellar {10-11}-{10-12} secondary twins (STs) appeared inside primary {10-11} contraction twins (CTs), with a morphology similar to the previously discovered {10-12}-{10-12} STs. However, through detailed misorientation calibration, it was determined that this type of secondary twin is {10-11}-{10-12} ST. Through calculation and analysis, it was found that the matrix was under compressive stress in the normal direction (ND) during fatigue deformation, which was beneficial for the activation of primary {10-11} CTs. The local strain accommodation was evaluated based on the geometric compatibility parameter (m') combined with the Schmid factor (SF) of the slip system, leading us to propose and discuss the possible formation mechanism of this secondary twin. The analysis results indicate that when the local strain caused by basal slip at the twin boundaries cannot be well transmitted, {10-11}-{10-12} STs are activated to coordinate the strain, and different loading directions lead to different formation mechanisms. Moreover, from the microstructure characterization near the entire fracture surface, we surmise that the presence of such secondary twins is not common. [ABSTRACT FROM AUTHOR]

It has been a common method to improve the mechanical properties of metals by manipulating their microstructures via static recrystallization, i.e., through heat treatment. Therefore, the knowledge of recrystallization and grain growth is critical to the success of the technique. In the present work, by using in-situ high temperature EBSD, the mechanisms that control recrystallization and grain growth of an extruded pure Mg were studied. The experimental results revealed that the grains of priority for dynamic recrystallization exhibit fading competitiveness under static recrystallization. It is also found that grain boundary movement or grain growth is likely to show an inverse energy gradient effect, i.e., low energy grains tend to swallow or grow into high energy grains, and grain boundaries of close to 30° exhibit superior growth advantage to others. Another finding is that {10–12} tensile twin boundaries are sites of hardly observed for recrystallization, and are finally swallowed by adjacent recrystallized grains. The above findings may give comprehensive insights of static recrystallization and grain growth of Mg, and may guide the design of advanced materials processing in microstructural engineering. [ABSTRACT FROM AUTHOR]

Hot torsion tests for AZ80 magnesium alloy were carried out in the temperature range of 380 °C-260 °C, with a constant decreasing temperature rate of 10 °C/s in order to weaken the basal texture and refine the grains. The results indicated that the average grain sizes were refined forming gradient structure with increasing specimen radial position from center (12.2–5.4 μm), and that the initial basal texture intensity of the extruded magnesium alloy was weakened from 46.2 to 8.3. Furthermore, the extension twins (ETs) could be disintegrated from the twins forming separated twins with smaller sizes. Interestingly, ETs with the same twin variant intersecting with each other could be coalesced forming grains with similar orientation, while ETs with different twin variants were separated by twins boundaries contributing to grain refinement. Moreover, in addition to the conventional continuous dynamic recrystallized (CDRX) grains with 30˚ orientation rotated around C-axis of the parent grains, CDRXed grains with 30˚ rotation around a-axis and random rotation axis were also discerned. Besides, the CDRX evolution induced twins were also elaborated, exhibiting the complex competition between CDRX and twining. Hot torsion deformation with constant decreasing temperatures rate is an effective way of grain refinement and texture modification. [ABSTRACT FROM AUTHOR]

Twinning, on par with dislocations, is critically required in plastic deformation of hexagonal close-packed crystals at low temperatures. In contrast to that in cubic-structured crystals, twinning in hexagonal close-packed crystals requires atomic shuffles in addition to shear. Though the twinning shear that is carried by twinning dislocations has been captured for decades, direct experimental observation of the atomic shuffles, especially when the shuffling mode is not unique and does not confine to the plane of shear, remains a formidable challenge to date. Here, by using in-situ transmission electron microscopy, we directly capture the atomic mechanism of the 11 2 ¯ 1 twinning in hexagonal close packed rhenium nanocrystals. Results show that the 11 2 ¯ 1 twinning is dominated by the (b1/2, h1/2) twinning disconnections. In contrast to conventional expectations, the atomic shuffles accompanying the twinning disconnections proceed on alternative basal planes along 1/6 1 1 ¯ 00 , which may be attributed to the free surface in nanocrystal samples, leading to a lack of mirror symmetry across the 11 2 ¯ 1 twin boundary. Atomic shuffles are important phenomena accompanying the twinning in hexagonal close-packed crystals, but the direct experimental observation on it is lacking. Here, the authors show the shuffling mechanism of {112 ̅1} twinning in rhenium nanocrystals by in situ transmission electron microscopy. [ABSTRACT FROM AUTHOR]

In the two-phase crystal EuRbFe4As4/EuFe2As2 (1144/122), a linear ordering of Abrikosov vortices, uncharacteristic for superconducting pnictides, has been found using the method of decorating with magnetic nanoparticles. The observed chains of vortices directed along crystallographic 〈110〉 axes of the orthorhombic EuFe2As2 phase are explained by pinning of vortices in the superconducting phase 1144 on linear defects associated with the twin boundaries of the non-superconducting 122 phase. [ABSTRACT FROM AUTHOR]

High-nitrogen austenitic steel (HNS) cold-rolled with a reduction rate of 25% was subjected to an investigation of the effect of annealing temperature on microstructural evolution, tensile properties and the variation in fracture surface morphology. In cold-rolled HNS, matrix recovery occurred at an annealing temperature of 600 °C, and recrystallization was locally initiated at an annealing temperature of 800 °C. The 0.2% offset yield strength (0.2% YS) and ultimate tensile strength (UTS) were almost constant up to an annealing temperature of 500 °C, and these values gradually decreased above the annealing temperature of 600 °C, while a sharp reduction in the percentage reduction in area (RA) occurred at the annealing temperatures of 600 and 700 °C due to Cr2N precipitation along the grain and twin boundaries. The ratio of 0.2% offset yield strength to ultimate tensile strength (0.2% YS/UTS) remained constant until matrix recovery took place; however, once recrystallization occurred, the ratio decreased significantly. Furthermore, the variation in the morphology of Cr2N along the grain boundaries in the annealing temperature range from 600 to 800 °C influenced the intergranular fracture morphology, resulting in a transition from dimple to ledge and back to dimple. [ABSTRACT FROM AUTHOR]

We construct and analyze a second-order parameter uniform numerical method for parabolic singularly perturbed space-delay problems with interior turning point. The considered problem's solution possesses an interior layer in addition to twin boundary layers due to the presence of delay. Some theoretical estimates on derivatives of the analytical solution, which are useful for conducting the error analysis, are given. The proposed technique employs an upwind scheme on a fitted Bakhvalov–Shishkin mesh in the spatial variable and implicit-Euler scheme on a uniform mesh in the time variable. This discretization of the problem is shown to be uniformly convergent of O (Δ τ + − 1) , where Δ τ is the step size in the temporal direction and K denotes the number of mesh-intervals in the spatial direction. Further, to improve the accuracy, we make use of Richardson extrapolation and establish parameter-uniform convergence of O ((Δ τ) 2 + − 2) for the resulting scheme. Numerical experiments are performed over two test problems for validation of the theoretical predictions. [ABSTRACT FROM AUTHOR]

Understanding the origin and mechanisms of magnetic damping in complex oxide materials is crucial for optimizing spin dynamics and tailoring their properties for specific spintronic applications. Ferromagnetic resonance spectroscopy (FMR) technique has been used to investigate the magnetic damping of multiple La2/3Sr1/3MnO3 (LSMO) epitaxial thin films with similar thickness and identical DC magnetic properties. However, the dynamic magnetic properties exhibit noticeable variations among samples. Microstructural analyses using X-ray diffraction (XRD) and atomic force microscopy (AFM), confirm that the samples are structurally identical, except for minute differences in the miscut angles of the substrates. Nevertheless, when examining the samples using backscattered electron (BSE) images in scanning electron microscopy (SEM), significant disparities in the twin distribution are observed. These variations in the twin distribution directly correlate with the observed differences in the damping values. A careful image analysis of BSE images allows to demonstrate that the increase of damping is due to the pinning of the magnetization in the twin boundaries. [ABSTRACT FROM AUTHOR]

[Display omitted] The microstructure of Au metal cocatalyst has been shown to significantly influence its optical and electronic properties. However, the impact of Au defect engineering on photocatalytic activity remains underexplored. In this study, we synthesize different Au-TiO 2 composites by in-situ hybridizing face-centered cubic (F-Au) and twin boundary defect Au (T -Au) nanoparticles (NPs) onto the surface of TiO 2. We find that T -Au NPs with twin defects serve as highly efficient cocatalysts for converting alcohols into their corresponding aldehydes while also generating H 2. The optimized T -Au/TiO 2 composite yields an H 2 evolution rate of 6850 µmol h−1 g−1 and a BAD formation rate of 6830 µmol h−1 g−1, about 38 times higher than that of blank TiO 2. Compared to F-Au/TiO 2 , the T -Au/TiO 2 composite enhances charge separation, extends the lifetime of electrons, and provides more active sites for H 2 reduction. The twin defect also improves alcohol reactant adsorption, boosting overall photocatalytic performance. This research paves the way for more studies on defect engineering in metal cocatalysts for enhanced catalytic activities in organic synthesis and H 2 evolution. [ABSTRACT FROM AUTHOR]

For decades, SrTiO3 has been in the focus of research with seemingly never-ending new insights regarding its ground state properties, application potentials, its surface and interface properties, the superconducting state, the twin boundaries, domain functionalities, etc. Here, we focus on the already well-investigated lattice dynamics of STO and show that four different temperature regimes can be identified which dominate the elastic properties, the thermal conductivity, and the birefringence. These regimes are a low-temperature quantum fluctuation-dominated one, followed by an intermediate regime, a region of structural phase transition at ~105 K and its vicinity, and at high temperatures, a regime characterized by precursor and saturation effects. They can all be elucidated by lattice dynamical aspects. The relevant temperature dependences of the soft modes are discussed and their relationship to lattice polarizability is emphasized. [ABSTRACT FROM AUTHOR]

This paper deals with the performance of sintered nano-silver bonds used as wide-bandgap power module die attachment technology. The paper specifically explores the fine-scale microstructures of highly porous sintered attachments under power cycling to provide a deeper understanding of the significance of porosity as a reliability-related microstructural parameter. Attachments prepared at 220°C using a pressure of 6 MPa for 1 s (parameters known to generate approximately 50% porosity from previous work) and subsequently subjected to 650,000 power cycles between 50°C and 200°C are assessed. A correlative workflow integrating x-ray computed tomography, focused ion beam (FIB) and electron backscatter diffraction (EBSD) data is applied to merge meso- and nanoscale microstructural features to illuminate the degradation mechanisms. The as-sintered Ag layer has a high volume of heterogeneously distributed pores, and consists of randomly oriented equiaxed grains whose sizes vary depending on the local density of the region sampled. Power cycling promotes grain growth and the loss of twin boundaries, and these changes are more pronounced within more dense regions of the Ag attachment. In contrast, the copper substrate appears to undergo some grain refinement, with deformation twins visible within finer-grained zones during power cycling. Cracks, which appear to start off within the Ag layer, propagate across the Ag-Cu boundary and transgranularly through fine-grained regions within the copper with little tortuosity. These observations are discussed within the context of reliability behaviour. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to investigate the influence of deformation degree on the microstructure and properties of a Ni-based superalloy. An upsetting experiment was conducted using a free-forging hammer to achieve a deformation degree ranging from 60% to 80%. The impact of the forging deformation degree on the hardness and high-temperature erosion performance was evaluated using the Rockwell hardness tester (HRC) and high-temperature erosion tester, respectively. The experimental results indicate that as the deformation degree increased, the hardness of the forged material progressively increased while the rate of high-temperature erosion gradually decreased. In order to comprehensively study the mechanism behind the variations in forging performance, optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were employed. The findings reveal that as the deformation degree increased, the presence of small-angle grain boundaries and an increase in grain boundary area contributed to enhanced hardness in the alloy forgings. Furthermore, it was discovered that grain boundaries with twin orientation promoted dynamic recrystallization during deformation, specifically through a discontinuous dynamic recrystallization mechanism. Additionally, the precipitated γ′ phase in the alloy exhibited particle sizes ranging from 40 to 100 nm. This particle size range resulted in a higher critical shear stress value and a more pronounced strengthening effect on the alloy. [ABSTRACT FROM AUTHOR]