Nature and origin of sliding-wear debris from steels

The mechanism of wear-particle formation during unlubricated sliding wear of several carbon and alloy steels has been investigated by scanning (SEM) and transmission electron microscopy (TEM). Individual debris particles are plate-like and typically 200 to 400 nm in thickness. The thinner particles are generally iron oxides except at low temperatures or in inert atmospheres when predominantly metallic particles result. The mean debris-particle width was 1 to 2 ..mu..m. TEM revealed a fine dislocation cell structure typical of large strain deformation to a depth of 10 to 50 ..mu..m. The subsurface cell dimensions and bending of pearlite colonies indicate that the shear strain near to the surface is at least 5. In many instances, a 200 to 300 nm wide zone of lower dislocation density, indicative of recovery, we noted immediately below the surface. Some cracks formed along dislocation cell walls at the boundary of the recovered zone; others were associated with decohesion of particle interfaces of subgrain triple points. Some oxidation then occurs during separation of the platelet from the parent material as a consequence of the highly pyrophoric nature of thin metal flakes. The sequence of the dry sliding wear process is discussed. 16 figures.