Numerical simulations of atomic-scale disordering processes at impact between two rough crystalline surfaces

Numerical calculations have been used to throw light on the mechanical deformation and the atomic mixing processes taking place when two different metallic systems collide at low temperature. To this end, two semicrystals terminating with a free surface were pushed each against the other at a given relative velocity. Surfaces of different roughness were considered under different impact conditions. Simple mechanical loads on plane surfaces did not induce any significant mixing of atomic species at the interface, observed instead in collisions involving either rough surfaces or plane surfaces undergoing a relative sliding. In the case of rough surfaces, the local contact between the semicrystals is initially sustained by surface asperities. The atoms there located experience thus sudden mechanical loads and an unusual localization of kinetic energy, which enhance their mobility and favor the mixing process. A diffuse interfacial region with a disordered structure correspondingly appears. Its structural features were not significantly modified by the thermal relaxation processes occurring after the compressive load removal.