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In this paper, molecular dynamics method was used to design the grain boundary (GB) segregation structure of solute atom Mo in nanocrystalline nickel, and the effect of the segregation structure on the migration and deformation mechanism of nanocrystalline Ni–Mo alloy boundaries was studied. The results indicate that the addition of solute atom Mo can cause segregation at GBs, and the yield strength and tensile strength of nanocrystalline Ni are significantly increased through solid solution strengthening. Mo atoms segregation result in an increase of the GB thickness and stability of the GB. In addition, by labeling GB atoms and tracking their diffusion trajectories, it was found that after adding Mo atoms, the probability of atomic diffusion at GBs decreased. This indicates that Mo atoms reduce GB energy and improve GB stability. Meanwhile, as the Mo content increases, the degree of atomic disorder increases, and the probability of GB migration decreases. This leads to the inability of grains to merge and inhibit their growth, effectively improving the mechanical properties of the material. As the strain increases, the number and length of dislocations increase, and a large amount of entanglement occurs at GBs. With the increase of Mo content, the number of dislocations decreases sharply, with Shockley dislocations having the highest number. Shockley dislocations interact with other dislocations and hinder their generation and movement, forming a more stable dislocation system structure and increasing the strength of the alloy. Our work focuses on observing the influence of GB segregation structure on the mechanical properties and deformation mechanism of nanocrystalline polycrystalline Ni–Mo alloys, establishing the mechanism of the influence of segregation structure on the stability and coarsening of nanocrystalline metal GBs, examining the influence of segregation structure on dislocation motion and GB migration process during deformation, and proposing positive research and development ideas and theoretical basis for designing nanocrystalline metal materials with excellent performance. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were utilized to investigate the mechanical properties of the Al–Co–Cr–Fe–Ni high-entropy alloy and observe atomic microstructure and internal dislocation line changes under different parameter conditions. The findings demonstrate that the mechanical properties of the AlCoCrFeNi3 high-entropy alloy are significantly superior to those of conventional alloys in ambient temperature. During the tensile process, the face-centered structure undergoes interconversion with other structure types, while the internal dislocation lines gradually increase. The presence of grain boundaries impedes dislocation movement, resulting in lower deformation capacity and tensile strength in polycrystals compared to single crystals. Enhancing Ni content, increasing strain rate, and decreasing temperature during tensile process contributes to the enhancement of the mechanical properties of material. Among these factors, the Ni content exerts the most significant influence on the mechanical properties of the material. [ABSTRACT FROM AUTHOR]

This study investigates the impact of initial temperature on the microstructure and mechanical properties of welded components, using molecular dynamics (MD). The stress–strain curves of the welded components, following various initial temperature treatments, revealed a double yielding phenomenon. Notably, there was a significant strain difference of 19.7% between the two yields. When the strain was loaded to the point of doubling yielding, stacking faults and twins covered the aluminum component part, while no such observations were made in the nickel component part. Additionally, tensile cracking occurred in the aluminum component part. The results indicate that treatment at varying initial temperatures alters the internal structure of the welded components. After the material yielded the first time, a significant number of disordered atoms and Shockley partial dislocations emerge, resulting in a substantial buildup of dislocation tangles and reduced dislocation migration rates. Consequently, the material exhibits a phenomenon of double yielding, with dislocation slip and deformation serving as the primary mechanisms. The optimal mechanical properties of the welded components achieved an initial temperature of 200 K. Additionally, the effect of tensile temperature on the mechanical properties of the welded components were analyzed, and similar observations of double yielding were made. The significant number of dislocation tangles served as a barrier to dislocation slip, effectively enhancing the material's mechanical properties. The simulation results provide theoretical support for the development of aluminum–nickel multilayer film self-propagation welding process. [ABSTRACT FROM AUTHOR]

Nanotwinned exist in crystals as coherent interfaces with low interfacial energy, which can not only improve the strength of metal materials, but also increase the ductility. In this manuscript, we have performed molecular dynamics simulations of the mechanical properties of a nano-columnar crystalline Cu-Ni alloy with different twin boundary spacing. It is found that the model without twin has a stacking fault tetrahedron composed of stair-rod dislocations, which results in a small change in dislocation density at the later stage of deformation, and the average stress after yielding is lower than that of the model with twin. During the deformation process, with the increase of Other atoms, the dislocation slip barrier is enhanced, the tensile strength is increased, and the yield phenomenon is delayed, which is more obvious with the decrease of twin boundary spacing. The dislocation density decreases with the decrease of the spacing of the twin boundary, and the dislocation segments become shorter. When the twin boundary spacing is 0.625 nm, the tensile strength is increased by about 71% compared with the model without twin structure. [ABSTRACT FROM AUTHOR]

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

Molecular dynamics was used to study the uniaxial tensile process of Ni–Co alloy with gradient nanotwin structure, and the microstructure and deformation mechanism of mechanical properties of gradient nanotwin Ni–Co alloy were studied from the micro perspectives of dislocation, twin layer and grain boundary movement. The results show that when the twin structure Ni–Co alloy is uniaxial stretched along the gradient direction and perpendicular to the gradient direction, the twin layer has different strengthening effects on the structure and strengthening mechanism, the stretching in different directions has greater influence on the dislocation movement and stacking fault nucleation of the nanogradient twin structure. The yield strength of Ni–Co alloy is 11.3 Gpa and 5.5 Gpa, respectively, after stretching along gradient and vertical gradient directions, Young's modulus reaches 221.16 Gpa and 127.90 Gpa. It is found that the gradient twin structure stretched along gradient direction has greater strength and the twin layer breaks into fragments and distributes in the system during the process of strain increase. At different temperatures, it was found that the strength and plasticity of the material decreased sharply with the increase of temperature, the dislocation density in the system also decreased with the increase of temperature, resulting in poor performance of the material. [ABSTRACT FROM AUTHOR]

The effects of gradient grain size and temperature on the mechanical properties of nanocrystalline nickel were studied by the molecular dynamics method, and the microstructure change process of size gradient nanocrystalline nickel under tensile load was characterized by Common Neighbor Analysis (CNA). The research results show that dislocations tend to generate stress concentration in small-sized grains during stretching, so the plastic deformation of the material always occurs in small-sized grains first. At the same time, through Dislocation Analysis (DXA), it was found that Shockley dislocation is the main factor affecting its mechanical properties, and the interaction between dislocations provides a certain contribution to the strength of the metal. In addition, yield strength, maximum tensile stress, and Young's modulus all decrease with increasing temperature, and the grain boundary atomic content and the degree of disorder are greatly increased. During the stretching process, the number of dislocations is greatly reduced, which leads to a reduction of their interactions, which is the reason for the reduction of the mechanical properties of the material. The above research results have positive meaning for the design of gradient nanocrystalline materials, and provide reference and help for the improvement of nanomaterial properties. [ABSTRACT FROM AUTHOR]

Herein, the effects of different Co content and temperature factors on the shear mechanical properties of nano‐polycrystalline nickel–cobalt alloy are analyzed by molecular dynamics (MD) simulations. It is found in the work that the highest shear modulus of 63.03 GPa is obtained when the Co content is 10%, attributed to the lattice distortion caused by the difference in the lattice parameters between two elements. During the shearing process, the multilevel twins are present with intensification of the deformation process, resulting in excellent dynamic shear performance. Shockley dislocations will drive the stacking faults and other partial dislocations to constitute a tetrahedral edge, and finally forms a tetrahedral structure. In addition, as the temperature of the shear environment increases, the highest strain and stress decrease. The grain boundary atoms increase significantly, and the atoms inside the grains decrease accordingly. As the degree of atomic disorder increases, the grain boundaries will melt gradually. The decrease of partial dislocation density can weaken the entanglement effect caused by dislocations. The previous conclusions promote the product development and application of nano‐polycrystalline alloys in the future, and provide important guidance significant for the engineering application of nickel–cobalt alloys. [ABSTRACT FROM AUTHOR]

This work utilizes in situ transmission electron microscopy–based nanopillar compression to investigate the effect of electrochemical cycling on the mechanical properties of LiCoO2. The ultimate strength of LiCoO2 in the pristine state, and after 1 and 11 cycles are 5.62 ± 0.22 GPa, 3.91 ± 1.22 GPa, and 2.27 ± 1.07 GPa, respectively. The reduced average yield strengths and the large standard deviations of cycled samples, relative to the pristine powder, are hypothesized to result from nonuniform accumulation of Li+ site‐point defects during cycling; either H+ or Li+ vacancies. Density functional theory calculations support our hypothesized link between a nonuniform Li site‐point defect distribution in the cathode and reduction in the materials cohesive strength. Cycling lithium cobalt oxide reduces its strength as a result of point defect accumulation. [ABSTRACT FROM AUTHOR]

This work utilizes in situ transmission electron microscopy–based nanopillar compression to investigate the effect of electrochemical cycling on the mechanical properties of LiCoO2. The ultimate strength of LiCoO2 in the pristine state, and after 1 and 11 cycles are 5.62 ± 0.22 GPa, 3.91 ± 1.22 GPa, and 2.27 ± 1.07 GPa, respectively. The reduced average yield strengths and the large standard deviations of cycled samples, relative to the pristine powder, are hypothesized to result from nonuniform accumulation of Li+ site‐point defects during cycling; either H+ or Li+ vacancies. Density functional theory calculations support our hypothesized link between a nonuniform Li site‐point defect distribution in the cathode and reduction in the materials cohesive strength. Cycling lithium cobalt oxide reduces its strength as a result of point defect accumulation. [ABSTRACT FROM AUTHOR]

To prevent porous Si 3 N 4 ceramics from absorbing moisture in practical application, a dense SiC NWs/α-Si 3 N 4 composite coating was fabricated using the two-step technology involving slurry and liquid infiltration method. The results revealed that the SiC NWs not only can promote densification sintering of the coating but also can reduce thickness of the coating effectively due to the block effect of the SiC NWs. Furthermore, the SiC NWs in the coating had a good interfacial bonding with α-Si 3 N 4 matrix, meanwhile the toughening effects of the SiC NWs involving crack deflection, crack branching, SiC NWs bridging and pullout, also presented during mechanical damage. The strengthening and toughening mechanisms of the SiC NWs not only enhanced mechanical properties of the coating but also raised significantly critical crack size (L), thereby which made the coating have a good ability for thermal shock resistance. After thermal shock at ΔT = 1000 °C for 15 times, water absorption of the coated porous Si 3 N 4 ceramics increased only to 7.21% from 4.54%, and its residual strength ratio was up to 83.4%. More importantly, the coating exhibited an ability for crack healing during thermal shock testing. All those above results indicated that as-prepared SiC NWs/α-Si 3 N 4 composite coating can meet the applied requirements in long-term extreme conditions. [ABSTRACT FROM AUTHOR]

Abstract: Nano-eutectic bulk 1080 carbon steel was prepared on glass and copper substrates by an aluminothermic reaction casting. The microstructure of the steel was analyzed by an optical microscope, transmission electron microscopy, an electron probe micro-analyzer, a scanning electron microscope and X-ray diffraction. Results show that the microstructure of the steel consisted of a little cementite and lamellar eutectic pearlite. Average lamellar spacing of the pearlite prepared on copper and glass substrates was about 230nm and 219nm, respectively. Volume fraction of the pearlite of the two steels was about 95%. Hardness of the steel was about 229 and 270HV. Tensile strength was about 610 and 641MPa and tensile elongation was about 15% and 8%. Compressive strength was about 1043 and 1144MPa. Compared with the steel prepared on copper substrate, the steel prepared on glass substrate had smaller lamellar spacing of the pearlite phase and higher strength, and low ductility due to the smaller spacing. [Copyright &y& Elsevier]

Abstract: Microstructure and mechanical properties of bulk nanocrystalline Fe3Al based alloy with 5wt.% Cu prepared by aluminothermic reaction before and after annealed at 873, 1073 and 1273K for 8h were investigated. Microstructures of the alloy before and after the annealing consisted of a Fe–Al–Cu matrix, a little Al2O3 sphere and Fe3AlC x fiber phases. The matrix of the alloy before the annealing was composed a nanocrystalline phase with disordered bcc crystal structure and a little amorphous phase. The amorphous phase disappeared after the annealing and Fe3Al phase with ordered DO3 structure appeared in the alloy after annealed at 1073 and 1273K in the matrix of the alloy. Size of the Fe3AlC x fiber phase increased with the annealing temperature. The alloy after the annealing had better plasticity, higher yield strength than that of the alloy before the annealing, and the alloy after annealed at 1273K had the highest yield strength. [Copyright &y& Elsevier]

The thermodynamic stability and mechanical strength of grain boundaries (GBs) govern many key properties of nanocrystalline or polycrystalline metals. In order to design novel Cu-based alloys with extraordinary properties and broaden the application scopes of Cu alloys, it is essential to clarify the effects of GB structure and composition on the stability and cohesion of Cu GBs. Firstly, the GB energies and works of separation of 12 Cu symmetrical tilt GBs with various GB orientations were figured out by using first-principles calculations, to link the GB properties with structures. Our results shown that the GB energies and works of separation of 12 Cu GBs are notably anisotropic. The GB energies for these GBs have an inverted and linear relationship with their works of separation. As to GB composition, the segregation tendencies of 8 alloying elements (Mg, Ca, Cr, Ni, Zn, Zr, Ag and Sn) in the Cu Σ5 [001](210) symmetrical tilt GB and their cohesive and embrittling effects on the GB were studied. It was found that all considered solutes excluding the element Ni can segregate to the Cu GB and thus play stabilizing roles into the Cu GB. Among 8 solutes, only the Zr and Cr segregations can improve the thermodynamic stability and fracture strength of Cu GB simultaneously. The GB strengthening effects of Zr and Cr segregations was attributed to their significant chemical contributions to the embrittling potencies, i.e., the presence of covalent-like bonding features in newly-formed Cu–Zr/Cr bonds. The reduction/increase of anti-bonding/bonding states below the Fermi level in Cu–Zr/Cr atomic pairs should be responsible for the GB stabilizing effects of Zr and Cr segregations. [Display omitted] • Zr and Cr segregation can strengthen Cu Σ5 [001](210) symmetrical tilt grain boundary. • Zr and Cr segregation can stabilize Cu Σ5 [001](210) symmetrical tilt grain boundary. • Grain boundary energy present inverted linear relationship with work of separation. [ABSTRACT FROM AUTHOR]