INTERPLAY BETWEEN STICK-SLIP MOTION AND STRUCTURAL PHASE-TRANSITIONS IN DRY SLIDING FRICTION

Simulations of dry sliding friction between a metal asperity and an in commensurate metal surface reveal unusual atomic processes. The latera l force exhibits a quasiperiodic variation with the displacement of an asperity; each period consists of two different stick-slip processes involving structural transitions. While one layer of asperity changes and matches the substrate lattice in the first slip, two asperity lave rs merge into a new one through a structural transition during the sec ond slip. This leads to wear. The lateral force decreases abruptly dur ing these slip stages, but it increases between two consecutive slips and resists the relative motion. The analysis of the order suggests th at each structural transition is associated with a first-order phase t ransition. Nonadiabatic atomic rearrangements during these phase trans itions involve a new kind of mechanism of energy dissipation in the dr y sliding friction.