Friction anisotropy at Ni(100)/(100) interfaces: Molecular dynamics studies

Abstract

The friction of surfaces moving relative to each other must derive from the atomic interaction at interfaces. However, recent experiments bring into question the fundamental understanding of this phenomenon. The analytic theories predict that most perfect clean incommensurate interfaces would produce no static friction, whereas commensurate aligned surfaces would have very high friction. In contrast recent experiments show that the static friction coefficient between clean but 45°misoriented Ni͑001͒ surfaces is only a factor of 4 smaller than for the aligned surfaces ( ϳ0°) and clearly does not vanish ͑ is defined as the rotation angle between the relative crystallographic orientations of two parallel surfaces͒. To understand this friction anisotropy and the difference between analytic theory and experiment, we carried out a series of nonequilibrium molecular dynamics simulations at 300 K for sliding of Ni͑001͒/Ni͑001͒ interfaces under a constant shear force. Our molecular dynamics calculations on interfaces with the top layer roughed ͑and rms roughness of 0.8 Å͒ lead to the static frictional coefficients in good agreement with the corresponding experimental data. On the other hand, perfect smooth surfaces ͑rms roughness of 0 Å͒ lead to a factor of 34 -330 decreasing of static friction coefficients for misaligned surfaces, a result more consistent with the analytic theories. This shows that the major source of the discrepancy is that small amounts of roughness dramatically increase the friction on incommensurate surfaces, so that misaligned directions are comparable to aligned directions.

Origin of static friction and its relationship to adhesion at the atomic scale

“…Similar sliding behaviors were also noted in Ref. 15 at Ni/ Ni interfaces. Figure 1͑b͒ also shows the slab velocity under the applied force, ͑discussed in greater detail in Sec.…”

“…This observation is in agreement with previous MD simulations for Ni/ Ni friction. 15 The static friction must originate from the atomic interaction across the interface, which can be quantified by the interfacial energy. For the three interfaces with nonvanishing static friction, no discontinuous equilibrium positions were observed.…”

“…8 To explain the universal occurrence of static friction, recent theoretical models have attributed the origin of static friction to weakly adsorbed mobile molecules, 9-12 glassy interface films, 13 material transfer, elastic deformation, 14 and surface roughness. 15 However, the atomic-scale origin of static friction is still an open question. Furthermore, little attention has been paid to the relationship between static friction and adhesion at the atomic scale.…”

Size effects on the melting of nickel nanowires: a molecular dynamics study

“…Given the exponents (n, m), c is determined by the equilibrium lattice parameter, and e is determined by the total cohesive energy. The Q-SC potentials have already been used to study structural transitions between various phases of Ni, Cu and other facecentered-cubic (FCC) metals [23][24][25]. For the For the simulation of the bulk system, we applied a cubic single crystal with 2048 atoms of the perfect FCC structure, and periodic boundary conditions that replicate the cube infinitely in all three spatial directions.…”

The uniaxial tensile deformation of Ni nanowire: atomic-scale computer simulations

“…In the present paper, MD simulations have been performed with the quantum corrected SuttenChen (Q-SC) type many-body force field modified by Kimura et al [24] in which the parameters were optimized to describe the lattice parameter, cohesive energy, bulk modulus, elastic constants, phonon dispersion, vacancy formation energy, and surface energy, leading to an accurate description of many properties of metals and their alloys [25][26][27]. We have simulated the tensile process of Ni nanowire at room temperature.…”