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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]

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]

Gradient nanostructured metals have become one of the research hotspots in the field of materials science due to their excellent mechanical properties and unique deformation behavior. In our contributions, the nanotwin gradient was introduced into the nanocrystalline Ni–Co alloy, and the influence of the gradient structure on the shear properties and microscopic deformation behavior was studied in order to reveal the strengthening mechanism. The gradient nanotwin Ni–Co alloy has elastic deformation and work hardening at the initial shear stage. The stress decreases after reaching the stress limit, and the uniform plastic deformation is maintained at the later stage. The excellent stability of fine twin layer and its effective hindrance to dislocation nucleation and movement can improve the strength of the material. In addition, the yield and work hardening of nanotwin gradient Ni–Co alloy are easy to occur at low temperature, and the stress–strain curve fluctuates obviously. At high temperature, the alloy is prone to plastic deformation, and the strength is reduced macroscopically. The higher the temperature is, the more difficult it is to yield. The results provide a solid theoretical basis for the design of Ni‐based alloys. [ABSTRACT FROM AUTHOR]

This paper constructs a single O and S functionalized Zr2N model for surface levelling and at the same time a series of bifunctional models with different functional group ratios and distributions. The influence of these functional groups on the electrochemical and lithium storage properties of Zr2N materials has been systematically investigated in terms of lithium atom adsorption, migration and lithium storage capacity. Among them, the theoretical lithium storage capacities of Zr2NO2 and Zr2NS2 with a low migration barrier are more than 755.02 and 678.30 mA h g−1, respectively. The results show that the O and S-functionalized Zr2N materials are all metallic and capable of adsorbing a certain number of lithium atoms. By controlling the ratio and distribution of the O and S functional groups, the adsorption position and adsorption energy of the lithium atoms can be influenced to a certain extent. Especially, the aim of improving the lithium storage performance of the material can be achieved in this way. [ABSTRACT FROM AUTHOR]

Using first principles calculations, we have confirmed the electronic and optical properties of 2D kagomes graphene doped with IVA elements (Si, Ge, Sn, Pb). The results show that Si-doped system has higher structural stability. The doping system increases the band gap of single-layer kagomes graphene, with Sn doping system being the most pronounced, and therefore can be considered as an attractive material for optoelectronic devices. The difference charge density and bonding population verify that the covalence of doping atoms and C atoms decreases, and that the degree of covalence diminution increases with increasing atomic number. The undoped kagomes graphene exhibits a strong light absorption capacity in the ultraviolet region, and the absorption peaks value decreases after doping, indicating that the element doping has a great weakening effect on the light absorption capacity, which has a certain potential significance for this material to be used as the antireflection film and wave permeable material of solar cells. In addition, the Pb and Sn-doped models possess the highest and lowest static dielectric constants, respectively. The peak value of electron energy loss is lower in the range of ultraviolet and visible wavelengths. These characteristics demonstrate that kagomes graphene offers substantial potential in the areas of optoelectronic and microelectronic devices. [ABSTRACT FROM AUTHOR]

Gradient induced unusual strain hardening achieves the equilibrium of the strength and plasticity of alloys, and is an important strategy for the optimization of the mechanical properties of metals and alloys. The segregation of solute elements can greatly improve the grain boundary stability, inhibit grain coarsening and promote the mechanical strength of the alloy. In our efforts, the segregation structure of the solute element Co was designed and added to the gradient nano Ni–Co alloy, and the two strengthening strategies were applied simultaneously in one structure. The mechanical strength of the alloy achieved a second increase based on the unique combination of gradient induced strain hardening and high plasticity, especially the yield strength of alloy increase amplitude reach to 42%. This provides a positive direction for the alloy strengthening strategy. In the process of secondary strengthening, the micro-mechanism is divided into two stages: in the first stage, the gradient strain provides the alloy with geometrically necessary dislocations and a multi-axial stress state, and the existence of large numbers of geometrically necessary dislocations creates good conditions for the second stage strengthening. In the second stage, the solute segregation induced stable grain boundaries produce a strong pinning effect on the geometrically necessary dislocation, which realizes the coupling of grain boundary strengthening and dislocation strengthening. This provides a new strengthening strategy and positive theoretical guidance for the experimental preparation of advanced alloys with excellent properties. [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]

In concentration gradient (CG) nano-polycrystalline Ni-Co alloy, the deformation mechanism of each region is different with the increase of Co content. It is found that in the Co-free region, grain boundary diffusion and dislocation slip mechanisms are dominant, while in other regions, there is a synergistic effect of solid solution strengthening. Moreover, the formation of new small grains by the migration of GB atoms will assist in the deformation of large grains, and the alloy exhibits gentle and stable stress–strain curve pattern. Meantime, although the dislocation density of each region is different, the dislocation density still changes stably before and after shearing. Compared with the uniform structure, the flow stress fluctuation is small when the CG structure is plastically deformed, which proves that this kind of structure is more stable. Moreover, it is found that at different temperatures, the CG alloy also shows stable dislocation density and coordination of various mechanisms, which ensures the strength stability. It is revealed that the CG structure has important properties that make the material strength more stable. This work demonstrates the excellent properties of CG alloy and has positive guiding significance for the development of low-cost, high-performance materials in terms of theoretical and practical applications. [ABSTRACT FROM AUTHOR]

The electronic structure and photocatalytic performance of GaSe/MoSSe and Ga2SSe/MoS2 heterojunctions are systematically investigated by means of first-principles calculations. The outcomes demonstrate that the IV and II stacking patterns feature the lowest binding energies and the shortest interlayer spacing, wherein the A stacking configurations show typical type-II band alignment characteristics which are conducive to fulfill effective separation of electron–hole pairs in space. The electrostatic potential and the CDD indicate the generation of built-in electric fields from MoSSe to GaSe layers and from Ga2SSe to MoS2 layers, respectively, in the interfacial domain, providing a theoretical basis for the examination of the photocatalytic mechanism. The two heterojunctions are more preferable for the photocatalytic decomposition of water under acidic and neutral atmospheres at dissimilar pH levels. For the GaSe/MoSSe heterojunction, the band gap follows a monotonic decreasing tendency when the tensile strain increases from 0% to 6%, while in the case of compressive strain, the band gap increases and then decreases, and the heterojunction cannot undertake the water oxidation process when the tensile strain surpasses 2%. Meanwhile, when a compressive strain of 0% to 3% is imposed, the heterojunction redox potential always traverses the redox potential of water, wherein the photocatalytic performance is sustained. For the Ga2SSe/MoS2 system, the band gap value decreases monotonically with the exertion of both tensile and compressive strains. Moreover, it is applicable to photocatalytic water decomposition in the strain range of −6% to 6%. The absorption coefficients reveal that the two heterojunction system has a higher peak in the visible range than the corresponding monolayer, indicating a higher light absorption intensity. Furthermore, the electron mobility of heterojunctions along both directions is significantly higher than that of MoS2 and WSe2 monolayers, and GaSe/HfS2 and K2Se/Cs2S heterojunctions. These findings propose that both GaSe/MoSSe and Ga2SSe/MoS2 heterojunctions can be utilized as potentially better catalysts for the photocatalytic decomposition of water. [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]

In this paper, the effects of rare earth elements on the bonding strength and stability of TiC/fcc-Fe interface are explored by using the first-principles method based on density functional theory. The results show that the Ti terminal is more stable than the C terminal in the process of forming the interface. The alloying elements tend to segregate at position 2 on the side of fcc-Fe. The segregation of Mo, Nb, Cr and Ce alloying elements increases the interatomic electron cloud enrichment and consumption between the interfaces and enhances the Fe–Ti interactions. The d orbitals of Mo, Nb, Cr and Ce and f orbitals of Ce have strong hybridization with Fe-d orbitals and Ti-d orbitals electrons near the Fermi energy level, indicating an increase in bonding strength and stability of the interfaces. When Fe atoms are replaced by W, Ni and Al atoms, the covalent bond strength between interfacial atoms is reduced, thus weakening the interfacial bonding strength. This provides solid theoretical foundation with regard to further application in austenitic heat-resistant steel fields. [ABSTRACT FROM AUTHOR]