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Abstract In this article, the friction and scratch characteristics of textured and rough surfaces of pure aluminum were studied using the quasi-continuum method. The surface profile of pure aluminum was altered with regular arrangements (bumps) and irregular arrangements (random surface roughness) along two orientations x[110] and y[001]. The surface smoothness and the internal strain of the material were studied through the scratching process. The effects of the ratio of the bump width to the bump pitch (W/P), scratching depth, average surface roughness (Ra) and indenter radius were examined. The results indicated that the surface smoothness was affected by the W/P ratio. Upon increasing the W/P ratio, the internal strain of the material became more intense. The greater Ra value the more severe impact. The coefficient of friction was found to be proportional to the scratching depth and indenter radius values. A scratching depth of 15 Å is suggested for optimal surface smoothness. Graphical abstract The surface effect and the internal strain on the scratching diagram with the same scratch depth of 15 Å for the four different W/P values. Image 1 Highlights • The friction and scratch characteristics of textured and rough surfaces of pure Al were studied using the QC method. • With the W/P = 100%, the material showed more dramatic changes. The smoothness was superior at the depth of 15 Å. • The friction coefficient increased proportionally to the scratching depth values. • With a greater indenter radius, the surface profiles are more arced and inclined after the scratching. [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]

• 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]

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]