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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]

Nanoindentation process is performed by molecular dynamics simulations to investigate the plastic deformation phenomena and mechanical properties of the polycrystalline tantalum (Ta) substrate. The comparison of mechanical behaviors between the single crystal and polycrystalline Ta is analyzed. The effects of grain size, indenter radius, indentation velocity, and temperature are deeply investigated. Further, the important factors of mechanical property such as the plastic deformation, dislocation, amorphization process, indentation force, yield pressure, and von Mises stress are evaluated. The results show that the phase transformations and dislocations almost absent in the grains. Instead, the dislocations densely occur in the grain boundaries, the amorphization regions are formed around the indentation areas and develop along the grain boundaries. The high von Mises stresses are mainly distributed around the indentation areas and in the grain boundaries. The single crystal tantalum shows better mechanical characteristics than the polycrystalline tantalum such as harder to deform, higher yield pressure, and lower dislocation. • The mechanical properties and plastic deformation phenomena of the polycrystalline Ta are investigated by MD simulations. • The dislocations densely occur in the grain boundaries. • The amorphization regions are formed around the indentation areas and develop along the grain boundaries. • The high von Mises stresses are mainly distributed around the indentation areas and in the grain boundaries. • The single crystal Ta shows the better mechanical characteristics than the polycrystalline Ta. [ABSTRACT FROM AUTHOR]

• Stacking faults are formed and the 〈1 1 2〉 dislocation occurs in the Cu layers. • The FCC structures are mainly transformed into the HCP structures in the Cu layers. • The ESBs are generated at the intersections of interfaces and stacking faults. • The tensile strength presents an agreement with the H-P relation as w 1 reduces. • The Cu/Cu 60 Ta 40 shows the best, while the Cu/Cu 40 Ta 60 shows the least plasticity. In this study, molecular dynamics method is used to investigate the plastic deformation phenomena and the mechanical properties of the crystalline/amorphous Cu/Cu x Ta 100-x nanomultilayers (CANMs) through the tension process. The effects of the layer numbers, layer width, components percentages, and cooling rate (CR) in the Cu-Ta metallic glasses (MGs) of the Cu/Cu x Ta 100-x CANMs are considered. The results exposethat in all cases, the deformation occurring in the Cu layers is more catastrophic than that in the Cu-Ta MGs layers. The embryonic shear bands (ESBs) are primarily generated at the intersections between the interfaces and stacking faults, then develop and expand within the Cu-Ta MGs layers to form the shear transformation zones (STZs). The constriction initiations appear at the junctions of the free surfaces and the interfaces in adjacent layers. For the Cu/Cu x Ta 100-x CANMs with different layer numbers, the wider Cu layer better restricts the shear bands (SBs) propagation in the Cu-Ta MGs layers. Moreover, the tensile strength presents an agreement with the Hall-Petch relationship as the layer number reduces. For the cases of the various layer widths , the plastic deformation increases with the decrease in the width of the Cu-Ta MGs layers (w 1). The tensile strength shows an agreement with the inverse Hall-Petch relationship as the w 1 reduces. For the cases of the various component percentages in the Cu-Ta MGs layers, the Cu/Cu 60 Ta 40 CANMs provides the best plasticity while the Cu/Cu 40 Ta 60 CANMs supplies the least plasticity. The tensile strength is higher with the larger Ta component percentages in the Cu-Ta MGs layers. The structure of the Cu 50 Ta 50 MGs is more stable, leading to the tensile strength of the Cu/Cu 50 Ta 50 CANMs increases as the cooling rate decreases. [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 simulations are used to investigate the plastic deformation behavior of Cu 50 Zr 50 /Cu amorphous/crystalline (A/C) multilayered nanofilms with different interface directions, number of layers and temperatures under the imprinting process. The results show that the loading force of multilayered nanofilms grows with increasing thickness of layers and decreasing temperature. Specifically, the maximum stress is larger with increasing layer thickness, this shows an inverse Hall-Petch relationship between the stress and the layer thickness. The local stress is focused around the stamp and rises up as increasing imprinting depth. The plastic deformation behaviors are realized by dislocations or stacking faults in crystalline layers and shear transformation zones (STZs) or shear bands in amorphous layers. Additionally, the propagation of shear bands or spatial correlation of STZs in an amorphous layer can be disrupted at the amorphous/crystalline interfaces (ACIs). The centrosymmetry parameter (CSP) and dislocation analysis (DXA) reveal the nucleation of stacking faults at the ACIs and the Shockley partial dislocation account for 80% in the total dislocations in all cases. The affected region extends and displacement of atoms becomes more irregular as increasing temperature. Besides, the radial distribution function (RDF) reveals the structure of the material is more stable at low temperature. The transverse interface specimens and thinner layer thickness, and high temperature are facilitated to material formability. The figure shows the CSP analysis and displacement vector of amorphous Cu 50 Zr 50 /crystalline Cu atoms under the imprinting process for different interface directions. Image 1 • The stress-layer thickness diagram is indicated in the inverse Hall-Petch relationship. • The shear band propagation depends on the different interface directions. • The nucleation of the stacking fault and dislocation mainly occur at the ACIs. • The Cu crystalline layers act as a barrier to the propagation of the STZs at the ACIs. • The direction of the interface affects greatly the displacement vector of the atoms. [ABSTRACT FROM AUTHOR]