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Low-temperature, low-pressure Cu-to-Cu direct bonding technology is a promising solution for next-generation high-density interconnects. Previous studies have shown that many properties of nanomaterials are determined by their structural characteristics. Therefore, the effect of the nanostructure (i.e., twin crystal and twin boundary, TB, sizes) on the bonding mechanism and mechanical response of the direct bonding of (111)-oriented nanotwinned Cu (NT-Cu) is studied using molecular dynamics simulations, where TB size means the TB layer thickness in terms of the number of atoms. The simulation results show that NT-Cu with extremely small twin crystals (e.g., 0.625 nm) have poor diffusivity. The number of dislocations induced by plastic deformation increases with increasing twin crystal size during stretching processes, degrading mechanical strength. The strain hardening of bonded NT-Cu with extremely small twin crystals (e.g., 0.625 nm) is dominated by the strong barrier created by a high density of TBs, whereas that with twin crystal sizes of 2.5–10 nm is dominated by dislocation–TB and dislocation–grain boundary interactions. Bonded NT-Cu with 2–6 atoms per TB layer exhibits softening at initial plastic deformation due to the onset of partial collapse of TBs; however, the strength then significantly increases with a further increase in strain due to strain hardening. [ABSTRACT FROM AUTHOR]

The microstructure evolution due to the tensile deformation of the equiatomic quinary high-entropy alloy Ho-Dy-Y-Gd-Tb (HEA-Fb) is assessed. HEA-Fb has extraordinarily similar alloying elements. It is one of the few hexagonal-close-packed single-phase representatives of HEA. HEA-Fb is compared to the equiatomic quaternary medium-entropy alloy (MEA) Ho-Dy-Gd-Tb with no Y (4-Y). For a hexagonal HEA, in contrast to the cubic HEA, little information on plastic deformation and underlying mechanisms is available. A detailed study using electron microscopy-based multi-scale characterization (SEM, S/TEM, and STEM-EDS) explains significant differences between the ductile behavior of the quaternary MEA 4-Y and the brittle behavior of the quinary HEA-Fb at room temperature. Twinning during plastic deformation is decisive for ductility, which challenges the widely discussed high-entropy effect on the mechanical behavior of the HEA. For the quaternary MEA 4-Y, a twinning-induced plasticity effect is found. In the latter, oxidized twins are present in the undeformed state. In both alloys, the twin orientations are indexed as [ 2 ¯ 201 ] , while the matrices have the perpendicular [ 11 2 ¯ 0 ] orientation. Additionally, the analysis of twin structures confirms the importance of twin boundaries as obstacles for dislocations and stacking fault mobilities. The results are discussed in the context of the existing knowledge gaps in the field of hexagonal MEAs and HEAs. [ABSTRACT FROM AUTHOR]

Understanding of dynamical responses and mechanical characteristics of metals and alloys at high strain rates holds significant importance in fundamental physics and optimizing the performance capabilities of materials. During high-speed impact scenarios, materials may be subjected to high pressure and plastic deformation, which have the potential to modulate their mechanical attributes. In this study, high-speed planar impact experiments were conducted to investigate the progressive alterations in the microstructures and mechanical properties in coarse-grain body-centered cubic (bcc) iron subjected to high-strain-rate (approximately 2.60–3.89 × 106 s−1) impact reaching approximately 15 GPa in a one-stage light-gas gun. The nanoindentation tests show that the nano-hardness of the post-shock iron improves 1.5 times from approximately 1.75–2.70 GPa. Microscopic analyses of the post-shock bcc-iron show no significant grain refinement but a noticeable increase in the twin boundaries (TBs) and low angle grain boundaries (LAGBs) proportion with increasing shock pressure. Therefore, the interaction between TBs, LAGBs, and dislocations in post-shock iron grains plays an important role in mediating its mechanical properties. Our findings serve as possible guidance for exploring the mechanical properties of single-crystalline and poly-crystalline iron-based materials, such as steel, with optimized mechanical performance. [ABSTRACT FROM AUTHOR]

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]

Manufacturing of metallic components using additive manufacturing technique is of great interest for the industrial applications. Here, the mechanical and microstructural responses of a 316 L stainless steel (316LSS) built by selective laser melting (SLM) with XOY and XOZ directions were revealed by performing in situ neutron diffraction tensile tests. The tensile strength of the XOY-printed samples reaches 700 MPa, while the tensile strength of the XOZ-printed samples is less than 600 MPa. The as-printed 316LSS exhibits anisotropy in tensile property due to the formation of different fractions of nano-sized dimples, twin boundaries, diffraction peak and lattice constants during tensile tests at room temperature. Therefore, choosing right printing direction plays a vital role in forming of metal parts using SLM for further application. [ABSTRACT FROM AUTHOR]

This study constructs a robust higher-order fitted operator finite difference method for a two-parameter singularly perturbed boundary value problem. The derivatives in the governing ordinary differential equation are substituted by second-order central finite difference approximations, after which the fitting parameter is introduced and determined. The resulting system of linear equations may then be solved using the Thomas method. The stability, consistency, and convergence of the current method have been thoroughly validated. To enhance accuracy and achieve a higher-order numerical solution, a post-processing technique was employed to upgrade the method from second-order to fourth-order convergence. Finally, three test examples were used to confirm the method's appropriateness. The numerical results demonstrate that the proposed technique is stable, consistent, and produces a higher-order numerical solution than the existing ones in the literature. [ABSTRACT FROM AUTHOR]

The nanoprecipitates and nanotwins enable to improve the mechanical performance of NiCo-based alloys. In this work, the molecular dynamics (MD) simulations are performed to investigate the strengthening mechanisms of nanotwinned medium-entropy NiCoCr alloys with various distributions and volume fractions of nanoprecipitates. MD simulations reveal that mechanical performance for the precipitates located in twin boundaries is better than that located in the twin lamellae. The precipitate-induced strengthening makes the nanotwinned NiCoCr alloys to achieve the maximum flow stress during increasing the precipitate volume fraction. The influences of volume fraction and distribution of the precipitate on winding and cutting mechanisms are analyzed comprehensively. The dislocation winding behavior, hindered twin boundaries deformation, and the adjacent precipitates connection control the precipitate strengthening mechanisms. A dislocation-based theoretical model is developed to forecast the size-dependent flow stress of nanotwinned metals with nanoprecipitates, in which the Orowan bypass mechanism and the dislocation pile-up behaviors are involved. The relationship between the microstructural size and the flow stress of nanotwinned metallic materials with nanoprecipitates is explored. The predictions for the flow stresses varied with the precipitate volume fraction are agreeable well with the results of MD simulation. The predicted maximum flow stresses and the corresponding critical volume fractions of nanoprecipitates are sensitive to the microstructural sizes. [ABSTRACT FROM AUTHOR]

All-inorganic halide crystal CsPbBr3 has gained significant attention due to its outstanding high-energy ray resolution capability and excellent environmental adaptability. However, due to the presence of structural phase transitions and thermal stresses, stress is prone to arise during the growth process of large-sized CsPbBr3 crystals, leading to defects such as cracks on the crystal surface, subgrain boundaries and twin crystals. These defects have severely impact on the performance of CsPbBr3 crystals. Currently, large-sized high-quality CsPbBr3 still can’ t be mass-produced through effective means, restricting its further application. Hence, conducting research on the growth and performance of large-sized CsPbBr3 crystals holds great theoretical significance and practical value. This paper briefly summarizes the fundamental properties, crystal preparation methods and research progress of CsPbBr3 crystals, mainly discussing the influencing factors of the vertical Bridgman growth method, and proposing novel optimization ideas for the growth of high-quality CsPbBr3 crystals. [ABSTRACT FROM AUTHOR]

With the indenter scratches the single-crystal, polycrystalline and polycrystalline-twin structures CoCrFeNiCu, these characteristics in various crystal nanostructures were found. Single-crystal structure CoCrFeNiCu has the strongest strength, but its wear resistance is weakest in the three types for the generating of long-range and same direction hexagonal closest packings (HCPs), because the long-range HCPs will move the internal atoms, making single-crystal structure CoCrFeNiCu has the most serious abrasive wear. However, the multigrain boundaries can isolate the damage of scratching, playing a lubrication role. Twin-polycrystalline CoCrFeNiCu has the best wear resistance in the three structures because of the hardening effects of twin boundaries. Our relevant research results can not only deeper the understanding about the different structural effects on the wear resistance mechanism of high-entropy alloys, but also provide the guidance for the material structure applications. Practical Applications: The data in this paper can provide a theoretical support for further enhancing the wear resistance of CoCrFeNi-Cu from changing the structures such as polycrystalline or polycrystalline-twin. For industrial applications, this paper can provide a suggest that the single-crystal structure CoCrFeNiCu should be used as a load-bearing material, polycrystalline structure CoCrFeNiCu should be applied in wear-resistant parts, and polycrystalline-twin as a perfect material can be used simultaneously in load-bearing and wear conditions. For example, in the field of marine machinery, the single crystal structure of HEA can be used as a skeleton and substrate to enhance its strength, and at the same time, the outer surface can be covered with a polycrystalline structure to isolate the internal wear of the hull by its water current. In the field of petroleum machinery, high-entropy alloys can maintain high mechanical properties under the premise of corrosion prevention and high temperature resistance, and in the internal structure, the mechanical properties can be enhanced with a single crystal structure, and the microscopic grains of polycrystalline CoCrFeNiCu coating can be used on the exterior to reduce wear. [ABSTRACT FROM AUTHOR]

A three‐dimensional (3D) microstructural volume is reconstructed from a stack of two‐dimensional sections which was obtained by serial sectioning coupled with electron back scattering diffraction (EBSD) mapping of a 316L austenitic stainless steel. A new alignment algorithm named linear translation by minimising the indicator (LTMI) is proposed to reduce the translational misalignments between adjacent sections by referencing to coherent twin boundaries which are flat and lying on {111} planes. The angular difference between the measured orientation of a flat twin boundary and that of the {111} plane is used as an indicator of the accuracy of the alignment operations. This indicator is minimised through linear translations of the centroids of triangular facets, which constitute grain boundaries at a distance not restricted by the in‐plane step size of the EBSD maps. And hence the systematic trend in the translational misalignments can be effectively reduced. The LTMI alignment procedure proposed herein effectively corrects the misalignments remained by other methods on a 3D‐EBSD data prepared using serial sectioning methods. The accuracy in distinguishing between coherent and incoherent twin boundaries is significantly improved. LAY DESCRIPTION: Accurately reconstructing the three‐dimensional (3D) microscopic structure of metal materials is crucial for exploring the relationship between the structure and properties of materials. Researchers utilise electron backscatter diffraction (EBSD) technique to sequentially acquire two‐dimensional (2D) images layer by layer, which are then stacked to reconstruct the three‐dimensional (3D) microstructure of the material. However, misalignments during this stacking process can result in an incorrect alignment between the layers, leading to distortion of the entire 3D volume. Previous methods aligned layers by making adjacent layers as similar as possible, but this could introduce cumulative errors. This work has proposed a new alignment method, 'Linear translation by minimising the indicator' (LTMI), which utilises coherent twin boundaries as additional references to guide the stacking process and accurately find the correct position between layers. Coherent twin boundaries serve as references because of their characteristics: these boundaries are special structures within the material, having a flat morphology and lying on specific crystal planes. Layers are shifted repeatedly until all the coherent twin boundaries in the sample display these characteristics, signifying that the layers are properly aligned. The LTMI method offers a way to significantly enhance the accuracy of 3D microstructural analysis, which is essential for designing materials that are strong and durable, with profound implications for the materials field. [ABSTRACT FROM AUTHOR]

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Fe35Ni35Cr20Mn10 high-entropy alloy wire with a diameter of 0.45 mm, prepared by continuous cold-drawing from a rod with a diameter of 6.34 mm, was subjected to high-temperature annealing at 600, 700, 800, 900, and 1000 °C for 1 h. The microstructure and mechanical properties in different states were investigated by microscopy observations and tensile testing. The wire in the as-drawn state exhibited the highest strength but the lowest elongation because of its fine multilayer structure and high dislocation density. Annealing, particularly at higher temperatures, considerably reduced the yield strength and caused significant recovery in both the elongation and strain-hardening exponent. Increasing the annealing temperature significantly decreased the dislocation density, notably coarsened the recrystallized grains, and significantly increased the fraction of twin boundaries and mean widths of annealing twins. The yield strength was found to be positively related to the dislocation density, and the elongation exhibited a negative relationship. In addition to the decrease in dislocation density, the formation of annealing twins played an important role in enhancing the elongation. [ABSTRACT FROM AUTHOR]

Na‐ion batteries (NIBs) have received considerable attention as promising alternatives to lithium‐ion batteries, particularly for low‐speed electric vehicles and large‐scale energy storage applications. Currently, layered oxide compounds are considered the most important cathode materials for NIBs. However, they suffer from reduced capacity and a shortened lifespan when exposed to water vapor during storage or battery assembly. This article elaborates on the structural and chemical evolution of NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode at the atomic scale in a pure water vapor environment. The Na+/H+ exchange induces the formation of a spinel‐like phase via a multi‐site nucleation mechanism. This transition preferentially occurs either at the cathode surface or along planar defects such as twin boundaries and grain boundaries. Additionally, numerous microcracks perpendicular to <003> direction appear inside NFM grains, further exacerbating the structural deterioration. Upon prolonged exposure to water vapor, NFM grains decompose into a mixture of Na2O and transition metal oxide nanoparticles (FeO, NiO, and MnO), accompanied by the generation of oxygen gas. This research provides a comprehensive atomic‐scale insight into the water vapor instability mechanism of layered oxide cathodes, offering guidance for the design and manufacture of the next generation of water vapor‐tolerant layered oxide cathodes in NIBs. [ABSTRACT FROM AUTHOR]

LiNiO2 remains a target for layered oxide Li‐ion cathode development as it can theoretically deliver the highest energy density of this materials class. In practice, LiNiO2 suffers from poor capacity retention due to electrochemically‐induced structural changes. While the impact of Ni off‐stoichiometry on the electrochemical performance has been extensively studied, that of planar defects present in the as‐synthesized cathode is not well understood. Advanced ex situ and operando structure probes are used to identify and quantify point and planar defects present in as‐synthesized Li1‐yNi1+yO2 cathodes and monitor their evolution during the first cycle. Specifically, a 7Li nuclear magnetic resonance (NMR) signature characteristic of Li environments near twin boundaries is identified; an assignment supported by first‐principles calculations and scanning transmission electron microscopy (STEM) images of twin boundary defects. The NMR results suggest that the concentration of twin boundaries depends on the amount of Ni excess. Moreover, operando magnetometry and ex situ synchrotron X‐ray diffraction and NMR demonstrate that these planar defects impede Li reinsertion into the bulk cathode at reasonable discharge rates and contribute to the first cycle irreversible capacity. These findings provide new design rules for Li1‐yNi1+yO2 cathodes, whereby a reduced concentration of twin boundaries in the pristine material leads to reduced kinetic limitations and improved cathode utilization. [ABSTRACT FROM AUTHOR]

Herein, the hot deformation behavior and microstructure evolution of N06625 superalloy are studied. Hot deformation behavior at 950–1200 °C and strain rate 0.1–10 s−1 are carried out by Gleeble‐3800 thermal simulator machine. The activation energy (Q) of the alloy is calculated by the change of stress–strain curve. The microstructure of the experimental material is characterized by electron backscatter diffraction, and it is found that the recrystallization fraction rate increases with the increase of temperature, but decreases first and then increases with the increase of strain rate. Discontinuous dynamic recrystallization is the main nucleation mechanism of N06625 superalloy. Continuous dynamic recrystallization (CDRX) is the auxiliary nucleation mechanism; CDRX gradually decreases with the increase of temperature. In addition, it is found that the evolution of special boundaries is closely related to the strain rate. The longer deformation time is beneficial to the interaction of grain boundaries, which leads to the special boundary fraction, and the increase of special boundary fraction can effectively weaken the preferred orientation caused by recrystallization growth. [ABSTRACT FROM AUTHOR]

LiNiO2 remains a target for layered oxide Li‐ion cathode development as it can theoretically deliver the highest energy density of this materials class. In practice, LiNiO2 suffers from poor capacity retention due to electrochemically‐induced structural changes. While the impact of Ni off‐stoichiometry on the electrochemical performance has been extensively studied, that of planar defects present in the as‐synthesized cathode is not well understood. Advanced ex situ and operando structure probes are used to identify and quantify point and planar defects present in as‐synthesized Li1‐yNi1+yO2 cathodes and monitor their evolution during the first cycle. Specifically, a 7Li nuclear magnetic resonance (NMR) signature characteristic of Li environments near twin boundaries is identified; an assignment supported by first‐principles calculations and scanning transmission electron microscopy (STEM) images of twin boundary defects. The NMR results suggest that the concentration of twin boundaries depends on the amount of Ni excess. Moreover, operando magnetometry and ex situ synchrotron X‐ray diffraction and NMR demonstrate that these planar defects impede Li reinsertion into the bulk cathode at reasonable discharge rates and contribute to the first cycle irreversible capacity. These findings provide new design rules for Li1‐yNi1+yO2 cathodes, whereby a reduced concentration of twin boundaries in the pristine material leads to reduced kinetic limitations and improved cathode utilization. [ABSTRACT FROM AUTHOR]

Refractory high‐entropy alloys (RHEAs) inspire the development of novel high‐temperature structural materials due to their outstanding resistance to softening and phase stability at elevated temperatures. However, they struggle to simultaneously achieve high‐temperature strength and room‐temperature ductility, while exhibiting insufficient room‐temperature strain hardening capability. Heterogeneous structure strengthening possesses a unique plastic self‐coordinated ability, which can effectively maintain strain hardening rate to achieve an excellent combination of strength and ductility. Benefiting from slow atomic diffusion, severe lattice distortion, and broad compositional design space, RHEAs with heterogeneous structures can be prepared from both chemical composition and interface structure perspectives. Chemical composition heterogeneity primarily focuses on fluctuations of alloying elements at the nanoscale, along with the formation of heterogeneous precipitates and unique lamellar eutectic structures. While, interface structure heterogeneity manifests in the activation of phase transformation and twin boundaries within grains, along with the formation of grains of vastly different sizes. The trend in RHEAs development is toward structural‐functional integration. Heterogeneous structures can also optimize functional properties, such as irradiation resistance, biomedical properties, and high‐temperature softening resistance of RHEAs. Finally, a brief outlook is provided on the future development direction of heterogeneous structure RHEAs. [ABSTRACT FROM AUTHOR]

Pb growth on a clean vicinal Si(557) surface at room temperature was studied using Scanning Tunneling Microscopy. The Pb film growth occurred in accordance with the Stranski-Krastanov scenario. The anisotropic wedge-shaped Pb-islands were observed on the top of a wetting layer. DFT simulations revealed the electron energy oscillations as a function of the island thickness agrees with the electronic growth model. The out-of-plane (111) Pb island consisted of stacked 2 nm thick layers. Based on the DFT simulations and proposed one-dimensional model, it was shown that the layers were separated by the twin boundaries. The energy of formation of twin boundary between the 2 nm layers exceeded the energy gain due to the quantum confinement effect. However, the electron standing wave at the Fermi level in the 2 nm layer made the hcp position of the Pb adatom on the Pb(111) surface favorable. The seed of the twin boundary formation was realized via occupation of the hcp position by the Pb adatom and dimers of adatoms on the Pb(111) surface. The adatom separation in dimers was controlled by an indirect interaction through conductive electrons at the Fermi level of the 2 nm layer of Pb. The completion of the Pb(111) atomic layer growth was achieved by an unusual collective superdiffusive mechanism in the wetting layer and on the top of the Pb nanoisland surface. A new mechanism of twinning boundary formation based on quantum effects in a system of conducive electrons was proposed. [ABSTRACT FROM AUTHOR]

Fractional calculus is an important mathematical tool that is widely used in control systems. It is established in the literature that fractional order models are more accurate and more effective in system modelling. In this study, an alternative and novel technique is proposed to identify the fractional order time-delayed model of an unknown system. The method is based on obtaining the approximate stability boundary locus (SBL) curve of the unknown system by applying three different experimental tests. Three points on the SBL curve are determined by the experimental tests and then the parameters of the fractional order time-delayed model are computed by solving the nonlinear systems of equation. The system model with double fractional order element plus a time delay is obtained using the proposed method. The proposed method is explained through simulations on a twin rotor system. The proposed method is also used in model order reduction calculation of the higher order transfer functions. [ABSTRACT FROM AUTHOR]

High entropy alloys have the potential to be processed at low temperatures and can be used at relatively high temperatures. However, there are some concerns regarding segregation of constituent elements and homogenization. In this regard, the study focuses on studying the significance of combining cryo-rolling and annealing in the context of grain boundary segregation. Furthermore, the study also focuses on the impact of cryo-rolling on the formation of micro-scale defect structures and evolution of recrystallized structure on annealing. Cryo-rolling induced a high density of slip bands and consequently high stored energy, which accelerated the kinetics of recrystallization, together with the formation of annealing twins of different morphology. The high degree of strain (defect structures) provided diffusion paths for atoms during annealing such that the micro-scale grain boundary segregation was not observed. [ABSTRACT FROM AUTHOR]

• Molecular dynamics simulation of interfacial defects on { 10 1 ¯ 1 } twin boundaries in magnesium. • Stabilities of single-atomic-layer-height disconnections connected with stacking faults. • Interactions between { 10 1 ¯ 1 } twin boundaries and basal mixed dislocations in the matrix. Single-atomic-layer-height disconnections that connect with I 1 stacking faults are produced on { 10 1 ¯ 1 } twin boundaries in pure magnesium through transmutation of basal 〈 a 〉 mixed dislocations across the twin boundaries, and their stabilities are examined using molecular dynamics simulations. The stable configuration for a single-atomic-layer-height disconnection is a pyramidal-basal (PyB) disconnection connecting an I 1 fault associated with a stacking sequence change of AB A CA, or a basal-pyramidal (BPy) disconnection connecting an I 1 fault associated with a stacking sequence change of BA B CB. A stable single-atomic-layer-height disconnection can transform to a less stable single-atomic-layer-height disconnection when its step orientation changes solely. A stable single-atomic-layer-height disconnection can also transform to another stable single-atomic-layer-height disconnection, when the step orientation of the disconnection and the type of the I 1 fault that connects with the disconnection change synchronously, and this process is accompanied with the emission of a Shockley partial dislocation from the twin boundary. [Display omitted] [ABSTRACT FROM AUTHOR]

• A high volume-fraction of nano-sized QLPSO phases has been achieved in Mg alloy. • The { 10 1 ¯ 2 } tension twin presents in high density QLPSO phase. • The strengthening role is mainly associated with the ∠86.3o QLPSO-TB. • The enhanced ductility is attributed to the ∠3.7o QLPSO-TB. Magnesium alloys with high strength in combination of good ductility are especially desirable for applications in transportation, aerospace and bio-implants owing to their high stiffness, abundant raw materials, and environmental friendliness. However, the majority of traditional strengthening approaches including grain refining and precipitate strengthening can usually prohibit dislocation movement at the expense of ductility invariably. Herein, we report an effective strategy for simultaneously enhancing yield strength (205 MPa, 2.41 times) and elongation (23%, 1.54 times) in a Mg-0.2Zn-0.6Y (at.%) alloy at room temperature, based on the formation of a nanosized quasi-long period stacking order unit (QLPSO)-twin structure by ultrahigh-pressure treatment followed by annealing. The formation reason and strong-ductile mechanism of the unique QLPSO-twin structure have been clarified by transmission electron microscopy observations and molecule dynamics simulations. The improved strength is mainly associated with the presence of nanosized QLPSO and the modified ∠86.3o QLPSO-twin boundary (TB) interface, effectively pinning dislocation movement. Comparatively, the enhanced ductility is related to the ∠3.7o QLPSO-TB interface and micro-kinks of nanoscale QLPSO, providing some paths for plastic deformation. This strategy on the QLPSO-twin structure might provide an alternative perspective for designing innovative hexagonal close-packed structural materials with superior mechanical properties. [ABSTRACT FROM AUTHOR]

The hot compression of the as-cast Fe-21Mn-0.7C–0.1Si twinning induced plasticity (TWIP) steel was investigated at the deformation temperature range of 950–1100 °C and strain rates of 0.01–5 s−1, using a GleebleTM thermo-mechanical simulator, to determine the hot deformation behaviour and analyse the recrystallisation mechanism. The results showed that the flow curves were characterised by yield-point-elongation (YPE) and dynamic recrystallisation (DRX) as the principal restoration mechanisms. The activation energy (Q) was calculated to be 394.975 KJ mol−1, which implies that the recrystallisation is sluggish in the whole range of the deformation conditions. Furthermore, the processing maps were generated according to the dynamic material model (DMM). The processing map was subdivided into different domains for the microstructural observations. The ideal hot deformation parameters of as-cast high Mn TWIP steel were obtained in the deformation condition range of 1087–1098 °C/10−1.2-10−0.17 s−1. Moreover, the microstructure analysis revealed that the DRX grains were twinned and nucleated through the bulging mechanism at the serrated grain boundaries, accompanied by twin boundaries migration created in the DRX grains by growth accidents, which contributed significantly to the growth of the DRX. [ABSTRACT FROM AUTHOR]

By tailoring different microstructural features, this study verifies that the laser powder bed fusion (LPBF)-fabricated Ti-6Al-4V titanium alloy with a fully α/β lamellar structure exhibits excellent ductility at liquid nitrogen temperature. HT-800 was obtained by holding at 800 °C for two hours and then furnace-cooled, resulting in a microstructure consisting of residual martensitic α' phase, lamellar α phase, and particulate β phase. The HT-900 was obtained by holding at 900 °C for two hours and then furnace-cooled, completely eliminating the multi-level martensitic α' phase generated during the LPBF process and resulting in an α/β lamellar structure. HT-900 achieved an elongation of 11% at liquid nitrogen temperature, a 47% improvement over the HT-800. After low-temperature strain fracture, the proportions of 61.38°<11–20> twin boundaries in the HT-800 and HT-900 were 21.4% and 26.4%, respectively, indicating that a substantial amount of deformation twinning is activated at liquid nitrogen temperature. Twinning induces the activation of slip systems by altering the orientation of surrounding grains. The coordinated plastic deformation of twinning and slip enhances the ductility of the HT-900 at 77 K. The results show that the LPBF-TC4 titanium alloy with a fully α/β lamellar structure exhibits superior, coordinated plastic deformation capabilities at 77 K, maintaining high strength while achieving greater ductility and fracture toughness. [ABSTRACT FROM AUTHOR]

To further investigate interaction and competition among various deformation modes in magnesium, a crystal plasticity model incorporating slip, twin, and secondary slip and twin systems is established. This study extends recent molecular dynamics findings to the crystal plasticity framework, introducing a new slip hardening model that incorporates twin boundaries. The proposed unified twin hardening model suitable for both tensile and compressive twins, considers twin stages of nucleation, propagation and growth, thereby simulating twin saturation and coexistence of multiple twin variants. Initially applied to single crystal magnesium, the numerical results agree with experimental findings by Kelley and Hosford, demonstrating twin saturation. We observe that plastic contributions from secondary slip and twin are smaller than those from slip and twins in the parent phase. Furthermore, the plastic contribution from pyramidal I slip is preferred to pyramidal II slip. Next, to study the serious influence of voids on the stress–strain response of ductile solids during manufacturing, the proposed model is then applied to single crystal magnesium containing a void along c -axis tension and compression. Both simulations confirm the validity of our crystal plasticity model and its potential to analyze future experimental and molecular dynamic findings. [ABSTRACT FROM AUTHOR]

In recent years, gradient nanotwinned copper, which features dual gradients in twin boundary spacing (TBS) and grain size (GS), has become a focal point of research in the materials science field. This structure has been proven to be an excellent nanotwinned system with a highly controllable microstructural gradient. In this study, a new inverse gradient nanotwinned (IGNT) copper structure model is constructed, where TBS and GS exhibit opposite trends. Molecular dynamics simulations are employed to explore the effect of the TBS gradient on the deformation behavior of this nanomaterial. In this study, it is found that the strength of IGNT copper increases with a larger TBS gradient. By analyzing the microstructural characteristics, it is observed that as the TBS gradient increases, the dislocation density gradually decreases and the fraction of hexagonal close‐packed atoms increases, leading to enhanced material strength. Additionally, with a higher TBS gradient, the appearance of hexagonal close‐packed atomic lines traversing the grains effectively hinders dislocation motion, further improving the material's strength. In this research, new insights are offered into the design of gradient nanotwinned copper structures and important theoretical support and guidance are provided for enhancing the mechanical properties of gradient nanotwinned copper. [ABSTRACT FROM AUTHOR]

The machinability of hard brittle nanocrystalline cubic silicon carbide (3C-SiC) is strongly dependent on internal microstructure and its adapted machining response. Here, we conducted molecular dynamic simulations to explore the machinability of nanotwinned 3C-SiC with a large number of twin boundaries in diamond cutting. The effect of the introduction of twin boundaries on the diamond cutting of nanocrystalline 3C-SiC, particular for its contribution to suppressing brittle fracture and improving ductile-mode cutting, was investigated in-depth. Our simulation results revealed that twin boundaries exerted a significant impact on the deformation mechanism and subsequent surface integrity of nanocrystalline 3C-SiC. Specifically, intergranular fracture was significantly suppressed by the introduction of twin boundaries. In addition, various deformation behaviors such as phase transformation, crack propagation, dislocation activity, and twin boundary-associated deformation mechanisms were operated in cutting process of nanotwinned 3C-SiC. Furthermore, the influence of twin boundary spacing on the diamond cutting characteristics of nanotwinned 3C-SiC was also addressed. [ABSTRACT FROM AUTHOR]

Sphalerite (ZnS) is a sulfide found in a large variety of ore deposits and is frequently hosted in metamorphic terranes that have undergone deformation and related recrystallization. However, the deformation mechanisms of sphalerite are still poorly understood because recrystallization evidence is barely visible under an optical microscope and may reflect complex and frequently multistage mechanisms. Furthermore, sphalerite may host up to a few thousands of parts per million of critical metals such as gallium (Ga), germanium (Ge), and indium (In). Metamorphic conditions and dynamic recrystallization may have induced local or total redistribution of these elements. Modern techniques such as electron backscattered diffraction analyses (EBSD) and laser-induced breakdown spectroscopy (LIBS) applied on sphalerite allow for the examination of grain boundaries, crystal-plastic deformation, and internal chemical diffusion, which classically reflect active deformation mechanisms. In this study, a microstructural and in situ chemical comparison between four sphalerite types (types 1, 2, 3, and 4) has been made for the first time. The four sphalerite types present different deformation imprints, although they are hosted in a similar geological setting: the Pyrenean Axial Zone and the Montagne Noire Variscan massifs (France). Based on EBSD and LIBS mapping, we describe two regional sphalerite growth stages composed of dark red crystals with polygonal shape (type 1, Bentaillou-Liat deposit) and light- to dark-brown euhedral crystals (type 3, Saint Salvy deposit). New investigation at microscale on sphalerite grains from the Saint-Salvy deposit shows late Cu-Ge-Ga enrichment not only in specific sector zonings but also along grain boundaries, growing crystal edges, and in low-angle misorientations or twin boundaries. Following a deformation event that probably occurred during the Pyrenean-Alpine orogeny, these two sphalerite mineralizations have both endured plastic deformation in a dislocation creep regime and dynamically recovered by subgrain rotation (SGR) mechanism. Two mechanisms of Cu-Ga-Ge spatial redistribution are observed and are key processes for the crystallization of Cu-Ga-Ge-rich minerals in sphalerite veins. The first mechanism involved the in situ redistribution of Cu-Ga-Ge contents from a pre-existing concentration in the sphalerite lattice (type 3, Arre deposit), creating Ge-sulfides (briartite), probably during Pyrenean-Alpine orogeny. Formation of this type of Ge-mineral may be related to solid-state diffusion processes. The second mechanism is associated with the circulation of a Cu-Ga-Ge-rich fluid in surrounding rocks. In the pre-existing polygonal sphalerite from Late-Variscan veins (type 2, Pale Bidau deposit), millimeter-size bands of small (<50 μm), recrystallized sphalerite grains are locally observed. Those domains contain inclusions of Cu (chalcopyrite) and Ga and Ge minerals (brunogeierite, carboirite). Fluid-induced diffusion in the polygonal sphalerite aggregates may occur with superimposed dynamic recrystallization, such as the Late-Variscan veins (type 2, Pale Bidau-type). During post-Variscan time, this fluid enriched in Cu-Ga-Ge largely circulated in the upper-crust of this Variscan terrane. This study highlights the key importance of coupled textural (EBSD) and in situ chemical analyses (LIBS) of diverse sphalerite types at a regional scale to indirectly unravel the origin of vein mineralization, and their related critical metal distribution. [ABSTRACT FROM AUTHOR]

Depending on whether the experiments are quasi-static or fast dynamics, the measured twin boundary velocity values range from zero to the material's sound speed. The twin boundary velocity is not yet predicted theoretically in the continuum mechanics framework. The extension of continual description is provided in the paper by means of internal variables. It is shown that a diffusional slow motion of twin boundaries can be represented using a single internal variable. The dual internal variable technique is employed for the description of the fast dynamics of twin boundaries. [ABSTRACT FROM AUTHOR]

An experimental setup has been developed that allows generating local bipolar electric and magnetic fields in a superconducting sample to study its magnetic, electronic, and crystalline microstates in one cycle. It is shown that the application of a damped oscillating local magnetic field to a superconducting sample induces an exponentially damped travelling magnetic wave. With decreasing wavelength and increasing wave energy, as more of the oscillations of the mentioned local field incident on the sample and twins, the induced travelling wave covers more and more twin boundaries and interacts with the L, C, R loops formed on them. This, in turn, leads to a gradual increase in the magnetic flux density in the trap and the residual resonant frequency of the oscillating circuit. [ABSTRACT FROM AUTHOR]

Nano‐twinned Cu pillar is fabricated on an as‐electroplated nano‐twinned Cu film, which preferentially grew in the {111} plane family. With a nano‐indentation device (Picoindenter), a vertical ultrahigh pressure of 5100 MPa is applied to the nano‐twinned Cu pillar. The twin lamellar grain is greatly deformed under that ultrahigh external stress. Consequently, the top surface plane is pressed into the lattice beneath to continuously form edge dislocations. Those dislocations are driven along the possible slip systems toward the outer surface of the first matrix lamella, corresponding to the plastic deformation. A dislocation‐mediated mechanism is proposed to explain the plastic deformation of the nano‐twinned Cu pillar. Three types of slip systems are identified for the created dislocations, each resulting in either the displacement on the first matrix lamellar grain or cross‐slip on the twin boundary. At the ultrahigh external pressure, as the dislocations slide through the twin boundary, they would dissociate to Shockley partial dislocations and alter the stacking sequence in the twin boundary, creating stacking faults. The resultant stacking faults in the twin boundary are observed in the transmission electro microscopy (TEM) lattice images. [ABSTRACT FROM AUTHOR]

Wide bandgap orthorhombic polymorph of gallium oxide (κ‐Ga2O3) possessing a high spontaneous polarization grown on wurtzite‐type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such κ‐Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual “suspended” thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR‐TEM) including cathodoluminescence (CL‐SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron–hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity. [ABSTRACT FROM AUTHOR]

The twin boundaries and inherent lattice strain of five-fold twin (5-FT) structures offer a promising and innovative approach to tune nanocrystal configurations and properties, enriching nanomaterial performance. However, a comprehensive understanding of the nonclassical growth models governing 5-FT nanocrystals remains elusive, largely due to the constraints of their small thermodynamically stable size and complex twin configurations. Here, we conducted in situ investigations to elucidate the atomic-scale mechanisms driving size-dependent and twin configuration-related aggregation phenomena between 5-FT and other nanoparticles at the atomic scale. Our results reveal that surface diffusion significantly shapes the morphology of aggregated nanoparticles, promoting the symmetrical formation of 5-FT, especially in smaller nanoparticles. Moreover, the inherent structural characteristics of 5-FT mitigate the dominance of surface diffusion in its morphological evolution, retarding the aggregation evolution process and fostering intricate twin structures. These findings contribute to advancing our capacity to manipulate the configuration of twinned particles, enabling more predictable synthesis of functional nanomaterials for advanced engineering applications. The mechanisms underlying the nonclassical growth of penta-twinned gold nanocrystals remain unclear. Here, the authors elucidate the atomic-level processes that drive size-dependent and twin configuration-related aggregation phenomena. [ABSTRACT FROM AUTHOR]

1D grain boundaries in transition metal dichalcogenides (TMDs) are ideal for investigating the collective electron behavior in confined systems. However, clear identification of atomic structures at the grain boundaries, as well as precise characterization of the electronic ground states, have largely been elusive. Here, direct evidence for the confined electronic states and the charge density modulations at mirror twin boundaries (MTBs) of monolayer NbSe2, a representative charge‐density‐wave (CDW) metal, is provided. The scanning tunneling microscopy (STM) measurements, accompanied by the first‐principles calculations, reveal that there are two types of MTBs in monolayer NbSe2, both of which exhibit band bending effect and 1D boundary states. Moreover, the intrinsic CDW signatures of monolayer NbSe2 are dramatically suppressed as approaching an isolated MTB but can be either enhanced or suppressed in the MTB‐constituted confined wedges. Such a phenomenon can be well explained by the MTB‐CDW interference interactions. The results reveal the underlying physics of the confined electrons at MTBs of CDW metals, paving the way for the grain boundary engineering of the functionality. [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]

The paper presents transmission and scanning electron microscopy investigations of the microstructure, dispersed particle precipitation and mechanical properties of the high-nitrogen austenitic steel VNS-53-Sh after 700 °C annealing for 10 h. It is shown that dispersed particles of Cr2N chromium nitrides and M23C6 carbides precipitate after annealing. The volume fraction of each particle type does not exceed 1%. Nitrides precipitate near the grain boundaries via discontinuous precipitation of austenite with the cell formation. Carbides precipitate at the grain boundaries and incoherent twin boundaries coherently with the austenite matrix. The dislocation density decreases by about an order of magnitude relative to the quenched state. Yield and tensile strength decrease respectively by ≈1.2 and ≈1.1 times relative to the initial state. Elongation to fracture increases by 1.6 times. It is found that the dislocation substructure recovery and precipitation of dispersed particles affect strength and plastic properties of the VNS-53-Sh. [ABSTRACT FROM AUTHOR]

High-entropy alloy (HEA) is a type of alloy that exhibits high hardness, strength, good wear resistance, corrosion resistance, and versatility. Molecular dynamics simulations were conducted to illustrate the microscopic evolution of FeNiCrCoCu HEAs under varying twin boundary spacing (TBS). Compression revealed dislocation migration, variations in the quantity and radius of nanovoids, as well as grain boundary diffusion. With increasing strain, high-energy regions expand on the surface of the crystal, transitioning from an initially smooth state to uniform deformation accompanied by grain boundary diffusion, while dislocations occur within the crystal. The number and radius of observed nanovoids within the crystal increase. The mechanical characteristics of FeNiCrCoCu HEAs are influenced by the TBS size. The alloy demonstrates better mechanical properties when the TBS is 1.22 nm. FeNiCrCoCu HEAs with a constant TBS showed improved mechanical characteristics when a greater number of grains (N) were present. According to the excellent mechanical properties of FeNiCrCoCu HEA, we established the original model and the effect of different grain number and twin spacing on its mechanical properties, and finally drew a series of conclusions. The above figure only intercepts the results of CNA, Atom Strain and Construct Surface Mesh for the case of TBS = 1.22 nm. [ABSTRACT FROM AUTHOR]

Ti48Al2Cr2Nb high-temperature alloy consisting of γ and α 2 phases, whose room-temperature brittleness limits its use in other lower temperature ranges, has been laser shocked to improve its surface properties. The study of the shock response and plastic deformation behaviour of material then provides further insight into the laser shock peening mechanism. In this paper, the molecular dynamics method and piston impact method are used to simulate laser shock peening of lamellar two-phase TiAl alloys to study the shock response and plastic deformation of material at different shock velocities, as well as the effects of shock velocity and two-phase interface on them. The results show that, in terms of shock response, the location of elastic–plastic wave separation as well as the atomic velocity and stress magnitude are affected by the shock velocity, elastic strain energy and interfacial energy, and some of stresses change significantly at the semi-coherent interface. At lower shock velocities, it is mainly stacking faults and twin boundaries in γ phase that initiate phase transitions across the interface to the α 2 phase, whereas at higher velocities, in addition to earlier α 2 phase transitions, clustered amorphous atoms and intermediate phases are also observed. The dislocations at the semi-coherent interfaces are affected by both interface type and shock velocity. The mechanical properties of lamellar two-phase TiAl are improved by the effect of laser shock at different shock velocities. These results provide experimental and theoretical guidance for improving the room-temperature properties of two-phase TiAl alloys. [ABSTRACT FROM AUTHOR]

The lattice mismatch between γ-CuI and Al2O3 (sapphire) is as large as 27.1% due to differences in crystal systems and lattice constants. To achieve epitaxial growth on the initial surface of the substrate, lattice mismatch can be minimized through domain matching. In this work, the γ-CuI film was epitaxially grown on the Al2O3(001) substrate by employing the physical vapor transport technology. The morphology, structure, and rotation domain matching of the films were investigated via SEM, XRD, electron backscatter diffraction, and STEM/TEM. The results revealed that the film grew preferentially along the (111) plane, and the full width at half maximum of the (111) diffraction peak in the rocking curve was 0.45°, which indicated the high degree of crystallinity of the film. The surface of the γ-CuI film exhibited two kinds of triangular crystal domains with a relative rotation angle of ∼60°. The interior of the crystal domains possessed a step-like structure. The two types of triangular crystal domains in the film were attributed to different rotation domains, and the interface was ascribed to the ⟨111⟩ 60° twin boundaries. The epitaxial matching mode was found to be CuI ⟨11 2 ̄ ⟩ (111)//Al2O3 [ 1 ̄ 1 ̄ 0] (001), resulting in ∼4.6% lattice mismatch between γ-CuI and Al2O3 along the Al2O3 ⟨ 1 ̄ 10 ⟩ direction, which is significantly lower than previously reported data. [ABSTRACT FROM AUTHOR]

Through the experiments of indium phosphide (InP) crystal growth, it was found that InP crystals with twin-free or low twinning probability can be grown repeatedly in the range of 0-90° growth angles at a high temperature gradient and low growth rate. Based on the experimental phenomena, it is inferred that twin formation is mainly related to undercooling at the growth interface. A kinetic model for twin nucleation based on the morphologies of the triple junction (tri-junction) region has been proposed from the point of view of the nucleation kinetics of crystal growth. It is found that when the undercooling of facets exceeds a critical value, the probability of twin nucleation increases with the increase of undercooling. When the twin boundary energy is 0.5 mJ m-2, this critical value approaches 0.2 K. Based on this model, the comprehensive influence of interface morphologies, temperature gradients, and growth rates on twin nucleation was analyzed. In addition, the effects of temperature fluctuations, constitutional supercooling, impurities and dopants have also been well explained. By controlling the morphologies of the growth interface under low undercooling, InP single crystals with a diameter of 170 mm were prepared using a flat shoulder method. [ABSTRACT FROM AUTHOR]

The microstructure–texture–tensile property relationships in a Ni‐containing medium‐Mn steel (Ni‐MMS), subjected to limited thermomechanical processing steps (i.e., hot forging and hot rolling), have been established in this study. The microstructure of the specimens hot rolled (HR) at 1173 (HR‐1173K) and 1373 K (HR‐1373K) exhibits ferrite and austenite phases. The austenite phase fraction in the HR‐1173K specimen is found to be higher than the HR‐1373K condition. The volume fraction of austenite to martensite transformation during tensile testing is also observed to be higher in the HR‐1173K specimen (≈13%) than the HR‐1373K condition (≈2%). This suggests the occurrence of more efficient transformation‐induced plasticity effect in the HR‐1173K specimen in comparison to the HR‐1373K condition, resulting in improved strength–ductility synergy in the former specimen. The smaller grain size of both the phases and higher fraction of twin boundaries as well the evolution of higher intensity γ‐fiber <111>//ND in the HR‐1173K specimen leads to better tensile properties. In addition, the overall activation of the primary slip systems (combination of face‐centered cubic and body‐centered cubic phases slip system), estimated through visco‐plastic self‐consistent simulation, is higher in HR‐1173K specimens, resulting in improved strain hardening response as compared to HR‐1373K one. [ABSTRACT FROM AUTHOR]

Developing non‐platinum group metal catalysts for the sluggish hydrogen oxidation reaction (HOR) is critical for alkaline fuel cells. To date, Ni‐based materials are the most promising candidates but still suffer from insufficient performance. Herein, we report an unconventional hcp/fcc Ni (u‐hcp/fcc Ni) heteronanocrystal with multiple epitaxial hcp/fcc heterointerfaces and coherent twin boundaries, generating rugged surfaces with plenty of asymmetric convex sites. Systematic analyses discover that such convex sites enable the adsorption of *H in unusual bridge positions with weakened binding energy, circumventing the over‐strong *H adsorption on traditional hollow positions, and simultaneously stabilizing interfacial *H2O. It thus synergistically optimizes the HOR thermodynamic process as well as reduces the kinetic barrier of the rate‐determining Volmer step. Consequently, the developed u‐hcp/fcc Ni exhibits the top‐rank alkaline HOR activity with a mass activity of 40.6 mA mgNi−1 (6.3 times higher than fcc Ni control) together with superior stability and high CO‐tolerance. These results provide a paradigm for designing high‐performance catalysts by shifting the adsorption state of intermediates through configuring surface sites. [ABSTRACT FROM AUTHOR]