The significance of near surface microstructure in the wear process

The wear process in which flake-like debris is developed and removed from the surface of metals in sliding contact is the direct result of heavy plastic deformation of a thin surface layer. The repeated ploughing of asperity contacts over a mating surface can produce high dislocation densities and eventual change in the microstructure to a cell-type structure found in heavily deformed metals. Cell sizes depend on material characteristics such as stacking fault energy, the applied stress and the temperature. It is shown that a cell structure can present many suitable pathways for subsurface crack generation and the release of thin wear flakes without the benefit of asperity cold welding and shear. Depth of crack formation and severity of wear can be associated with stacking fault energy. Changes in the microstructure caused by frictional heating or change in strain rate can cause abrupt changes in wear mode.