Atomic simulations of kinetic friction and its velocity dependence at Al/Al and -Al2O3/ -Al2O3 interfaces

Kinetic friction during dry sliding along atomistic-scale Al 001 /Al 001 and -Al2O3 0001 / -Al2O3 0001 interfaces has been investigated using molecular dynamics MD with recently developed Reactive Force Fields ReaxFF . It is of interest to determine if kinetic friction variations predicted with MD follow the macroscopic-scale friction laws known as Coulomb’s law for dry sliding and Stokes’ friction law for lubricated sliding over a wide range of sliding velocities. The effects of interfacial commensuration and roughness on kinetic friction have been studied. It is found that kinetic friction during sliding at commensurate -Al2O3 0001 / -Al2O3 0001 interfaces exceeds that due to sliding at an incommensurate -Al2O3 0001 / -Al2O3 0001 interface. For both interfaces, kinetic friction at lower sliding velocities deviates minimally from Coulombic friction, whereas at higher sliding velocities, kinetic friction follows a viscous behavior with sliding damped by thermal phonons. For atomically smooth Al 001 /Al 001 , only viscous friction is observed. Surface roughness tends to increase kinetic friction, and adhesive transfer causes kinetic friction to increase more rapidly at higher sliding velocities.