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The effects of grain size (GS) and distance between twin boundaries (d) on the tensile properties of nanocrystalline (NC) face-centered cubic Cu50Ni50 alloy are studied using the molecular dynamics simulations. The common neighbour analysis, dislocation extraction algorithm, shear strain, and von Mises stress configurations together with the total dislocation length, stress–strain relation, and tensile strength diagrams are presented to investigate the mechanical characteristics of the NC Cu50Ni50 specimens. The results exhibits that the twin boundaries significantly restrict the formation and propagation of the stacking faults. The integral deformation occurs under a combination of displacement, breakage, and self-destruction of the twin boundary along with the contraction and expansion of the grains. The tensile strength increases as the GS and the d increase, which agrees with the inverse Hall-Petch relation. The tensile strength of the conventional NC is higher than that of the twinned NC for each pair of specimens with the same GS. [ABSTRACT FROM AUTHOR]

Void growth and void coalescence in Cu-Ta metallic glasses (Cu 50 Ta 50) under the tensioning process at room temperature and a strain rate of 108 s−1. • The tensile strength of two-void specimen is higher than one-void specimen, however, it is faster destroyed. • The tensile strength decreases as the increasing size scale. • The tensile strength and g(r) value decrease as the increasing temperature. • The tensile strength significantly increases at a strain rate of 5 × 109 s−1 compared to 108 and 109 s−1. • Cu 20 Ta 80 MGs specimen seems to be relatively more crunchy and harder than other cases. In this study, molecular dynamics (MD) simulations were executed to investigate the deformation mechanisms and mechanical properties of Cu-Ta metallic glasses (MGs) nanofilms with one- and two-void defect under the tensioning process. The deformation behavior is evaluated through the void growth and void coalescence mechanisms of specimens. The influences of the specimen size scale, temperature, strain rate and component concentration in Cu x Ta 100−x MGs are assessed by stress-strain response and radial distribution function (g(r)) diagram. The results indicate that with the Cu 50 Ta 50 MGs specimens that possess the same number of atoms, the tensile strength of two-void specimen is higher than one-void specimen, however, it is faster destroyed. The tensile strength decreases as the increasing size scale and the tensile strength of one-void specimen is lower than the tensile strength of two-void specimen. As the increasing temperature, the tensile strength and g(r) value decrease. In the case of various strain rates, the tensile strength values slightly rise up at strain rates in the range from 108 to 109 s−1, however, it significantly increases at a strain rate of 5 × 109 s−1. The Cu 80 Ta 20 MGs specimen seems to be relatively softer and more flexible, while the Cu 20 Ta 80 MGs specimen seems to be relatively more crunchy and harder. [ABSTRACT FROM AUTHOR]

Abstract In this study, the incipient plasticity and voids nucleation of nanocrystalline gold were investigated using a molecular dynamics simulation. The effects of mean grain size and temperature were evaluated in terms of the material's stress-strain diagram, Young's modulus, yield strength, common-neighbor analysis, slip vectors, and deformation behaviors. From the stress-strain diagram, at 300 K, the maximum stress value corresponding to a grain size of 3.2 nm was much lower and the stress curve was clearly different from those corresponding to other grain sizes. Young's modulus increased with increasing mean grain size. The inverse Hall–Petch relation was observed. The slip was the main deformation behavior at a mean grain size of 3.2 nm. Moreover, the internal stress was more pronounced with increasing temperature. At 700 K, the main deformation area range was concentrated in the lattice at the middle of the samples, resulting in an almost force–induced structural transformation phenomenon in the middle. Void damage occurred at the junction of three–grain boundaries during the tensile process. With decreasing mean grain size, the less internal differential slip was generated under the same temperature and strain conditions. Graphical abstract The atomic motion and distance at the instant of stretching at an interval of 5 ps for a velocity field with GSs of 6.1 nm (a) and 12.4 nm (b) with conditions at temperatures of 300, 500 and 700 K, the strain of 0.13. Image 1 Highlights • The grain size of 3.2 nm has special properties compared to others. • The inverse Hall-Petch relation is observed at GSs of 7.6 nm and 10.2 nm. • The voids mainly occurred and expanded around the middle segment. • The rotating motion inside the lattices at a grain size of 6.1 nm. • The slip interface that mainly appeared along a 45° angle. [ABSTRACT FROM AUTHOR]

By using molecular dynamics simulations, the nanoimprinting process was performed to evaluate the mechanical properties and elastic recovery of the CuAgAu metallic glasses. The influences of cooling rate, stamp velocity, temperature, and percentage of the Cu-Ag-Au elements were considered in detail. By changing the imprint conditions, the mechanical responses of the nanocrystalline CuAgAu metallic glasses were mentioned and analyzed. Some important mechanical factors such as imprint force, shear strain, shear transformation zones, the fraction of atoms with high shear strain, and elastic recovery ratio were significantly influenced by changing the simulated conditions and deeply discussed. [ABSTRACT FROM AUTHOR]

• The STZs are mainly formed around the indentation region in the Cu x Ta 100-x layers. • The peak force for the 4-layer ACNLs is much higher than that for the 10-layer ACNLs. • The f 0.05 at the v = 100 m/s is remarkably higher than that in the other cases. • The damage degree of the CuTa/Cu ACNLs increase as the t increases. • As increasing Cu component percentage in the CuTa MGs, the recovery ratio increase. Through molecular dynamics simulations, the nanoindentation with the cylindrical indenter is carried out on the amorphous Cu x Ta 100-x /Cu crystalline nanolaminates (ACNLs). With changing the number of layers, penetration speed, experiment temperature, and composition distribution in the Cu x Ta 100-x layers, the nanoindentation characteristics and recovery capacity of the ACNLs are studied. By inserting the Cu crystal phases into the Cu x Ta 100-x bulk metallic glasses, the formation and development of the shear transformation zones are inhibited, resulting in the plasticity of the Cu x Ta 100-x is enhanced. The typical mechanical factors such as shear strain, von Mises stress, recovery ratio, indentation force, and dislocations of the ACNLs are significantly affected by changing the experiment conditions and profoundly discussed. [ABSTRACT FROM AUTHOR]

• The phase transition from FCC to HCP occurs in the Cu layers. • The atoms with high shear strain concentrate into the diagonal strips that create with the horizontal direction a angle of 45°. • The Cu/CuTa CANMs with more layers are more easily damaged. • As the percentage of Cu element increases, the sample becomes more flexible and softer. • The sample is harder and more brittle as the percentage of Cu element decreases. Through the tensioning process using molecular dynamics simulation method, the mechanistic properties of the Cu/CuTa crystalline/amorphous nanomultilayers (CANMs) are explored. In the Cu layers, the phase transition from FCC to HCP occurs. The embryonic shear bands (ESBs) essentially appear from the crossing positions of the stacking faults and interfaces, after that, grow to establish the shear transformation zones (STZs). The great shear strain atoms concentrate into the diagonal strips that create with the horizontal direction an angle of 45°. The Cu/CuTa CANMs with more layers are more easily damaged. For the cases with the different w 2 values, the f 0.3 value reduces with the increase of the w 2 value. The tensile strength increases with the w 2 increases and the inverse Hall-Petch relation is observed. For the Cu/Cu 10 Ta 90 , Cu/Cu 25 Ta 75 , and Cu/Cu 90 Ta 10 CANMs, the shrinkages are explicit, the formation of the STZs is more obvious than that in the Cu/Cu 50 Ta 50 , Cu/Cu 75 Ta 25 specimen. [ABSTRACT FROM AUTHOR]

Nanoindentation process is performed by molecular dynamics simulations to study the plastic deformation phenomena and mechanical properties of the amorphous/nanocrystalline Cu x Ta 100-x /Cu nanolaminates. The influences of the number of Cu layers, indenter velocity, temperature, and percentage of the Cu–Ta component are systematically assessed. By introducing the Cu nanocrystalline layer and controlling its thickness, the shear bands propagation and the expansion of plastic deformation are restricted. Further, the important factors of mechanical property such as indentation force, hardness, recovery ratio, von Mises stress are significantly affected by adding Cu nanocrystalline layers and changing the working conditions. Based on simulation results, dominant deformation mechanisms and phenomena of the amorphous/nanocrystalline Cu x Ta 100-x /Cu nanolaminates are propounded and deeply discussed. Image 1 • The mechanical phenomena of the CuTa/Cu nanolaminates are studied by MD method. • The plastic deformation zone increases as the number of layers increases. • The hardness and the average von Mises increases at a higher velocity. • The recovery ratio and the average von Mises increase as the temperature rises. • The Cu 75 Ta 25 /Cu is more flexible, while the Cu 25 Ta 75 /Cu is more crunchy and harder. [ABSTRACT FROM AUTHOR]

• The 〈1 1 2〉 and 〈1 1 0〉 dislocations are mostly formed in the Cu layers. • The defects occur in the interface and then extend towards the Cu layers. • For the horizontal layers specimens, the defects also appear in the Ta layers. The deformation behavior, the fracture mechanism, and the mechanical properties of the Cu/Ta nanoscale metallic multilayers (NMMs) with the vertical and horizontal layers under the tension process are meticulously studied using molecular dynamics (MD) simulations. The influences of the various temperatures, strain rates and modulation periods (λ) are evaluated in detail through the dynamic responses, the stress-strain relationships, and the dislocation density diagrams of the Cu/Ta NMMs. The results reveal that the phase transitions from the FCC structures into the HCP, BCC, and amorphous structures mainly occur in the Cu layers. Only a small amount of the BCC structures transforms into the amorphous structures in the Ta layers. In the Cu layers, the 〈1 1 2〉 and 〈1 1 0〉 dislocations are mostly formed, while the 〈1 1 1〉 dislocations are mostly found in the Ta layers. The defects occur in the interface and then extend towards the Cu layers for the vertical layers specimens. For the horizontal layers specimens, the defects appear both in the Ta layers and in the interface. The tensile strength of the vertical layers specimens is lower than that of the horizontal layers specimens under the same testing conditions. As increasing temperature, the tensile strength and the dislocation density reduce. However, the tensile strength and the dislocation density increase with an increase in strain rate. The tensile strength slightly changes with the different λ. The dislocation density is higher with a larger λ. [ABSTRACT FROM AUTHOR]

• Friction efficiency is significantly dependent on layer thickness and surface layer property. • Local deformation is hindered by the interface, resulting in very few plastic defects below the interface. • Surface layer property or interface controls the plastic deformation of the layer thickness variation. • Friction coefficient is related to the thermal softening and strain rate hardening of the material for different scratch rates. The tribological performance of CuTa/CuTa amorphous/amorphous nanomultilayers is investigated through molecular dynamics simulation in the present work. There is a significant effect of layer thickness and surface layer properties on scratching force, which results in reduced friction efficiency with small layer thickness for Cu 80 Ta 20 /Cu 20 Ta 80 specimen, while the frictional performance between the two models of Cu 80 Ta 20 /Cu 20 Ta 80 and Cu 20 Ta 80 /Cu 80 Ta 20 exhibits the opposite at the critical layer thickness of 1.5 nm. It is found that the surface layer property controls plastic deformation for specimens with great layer thicknesses, while the interface plays a significant role in plastic deformation with small layer thickness. For the increase in scratching speed, the friction coefficient tends to gently decrease for a cutting depth of 1.0 nm, and it increases slightly for machining depths of 2.0 nm and 2.5 nm in relation to the thermal softening and strain rate hardening of the material. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations have been employed to simulate the deposition process of Cu and Ni atoms on the Ni (001) substrate with the different compositions in the Cu x Ni 100-x film. Then, the mechanical characteristics of Cu x Ni 100-x /Ni substrate are investigated during the nanoindentation process. The deformation behavior in the nanoindentation process is also investigated when the parameter for velocity, temperature changes. The lattice constant of CuNi alloy increases as Cu content in CuNi alloy rising. In the case of different contents of Cu atoms, the force, hardness of the Cu x Ni 100-x /Ni substrate reduce as increasing the content of Cu. The shear strain and von Mises stress region increase as increasing the temperature and the loading velocity after the loading process. The plastic and elastic deformation of the Cu x Ni 100-x /Ni substrate formed during nanoindentation. The force and hardness of the Cu x Ni 100-x /Ni substrate reduce as increasing the temperature. In addition, with the higher loading speed, the force and hardness values become larger. The dislocation density increases as increasing the indentation depth after the loading process. The specimen of the deposition Cu x Ni 100-x on Ni(001), the specimen Cu x Ni 100-x /Ni substrate and shear strain in the nanoindentation process. Image 1 • As Cu content in Cu x Ni 100-x film rises the lattice constant of deposited CuNi film increases. • The high-shear strain area of the Cu x Ni 100-x /Ni substrate propagates to interface in the indentation process. • The force, hardness of Cu x Ni 100-x /Ni substrate decreases as increasing the content Cu and temperature. • The force, hardness of Cu 40 Ni 60 /Ni substrate increases as increasing the loading velocity. • The dislocations density increases as increasing the temperature and the loading velocity. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation is used to simulate the deposition and annealing process of Cu atoms on the Ni (001) trench. The results indicate that the curvature of profile and surface roughness of the Cu layer film decrease as increasing the substrate temperature and/or incident energy. The surface roughness of the deposition Cu film is variability as increasing the incident angle from 0° to 30°. In the growth process, the intermixing occurs at the interface between Cu atoms and Ni trench, and the length increases as the increasing of substrate temperature and/or incident energy. These phenomena may be attributed to the enhanced atomic mobility for higher incident energy and thermal annealing. The peak-to-peak distances of g(r) clearly indicate that the crystal structure of Cu–Ni atoms after the annealing process is improved, and still FCC structure. The dislocation is formed during the deposition process and affected by the substrate temperature, as well as the incident energy. The annealing treatment reduces the residual stress in the deposited Cu layer. The formation of the vacancies appears during the deposition process. After the annealing process, the Cu–Ni atoms become more orderly in the crystal lattice, many vacancies and voids are destroyed. In addition, the surface of the Cu film layer becomes smoother. The morphology, surface monolayer of the deposition copper on nickel trench by molecular dynamics simulation with the deposition parameters of 0°; 300 K, 700 K; 0.5, 2 eV. Image 105 • The surface roughness of the Cu film decreases with increasing the substrate temperature and/or incident energy. • The Cu film after annealing becomes smoother and more ordered. • The length of the Cu-Ni atoms intermixing increases as increasing substrate temperature and/or incident energy. • The 〈112〉, 〈100〉 and 〈110〉 dislocation is formed during the deposition process. • The deposition of the Cu atoms on the Ni trench is more difficultly performed as of ratio Depth/Width equals or larger than 2. [ABSTRACT FROM AUTHOR]