Metal surface layer structure formation under sliding friction

Changes in the surface layer structure of low carbon steel during sliding contact under reciprocating motion were investigated. A cellular structure with considerable disorientation between neighbouring cells forms in the subsurface layers of the metal owing to plastic deformation. The formation of a fully developed fragmented structure causes an increase in the metal flow limit and the presence of this structure determines the existence of mild or severe wear under frictional contact. The surface layers of the metal were examined by transmission electron microscopy and the wear mechanism during sliding was elucidated using fatigue theory; the form and size of the wear particles was predicted. The size of the wear particles was comparable with that of the cells formed by sliding contact. Cell boundaries oriented normal to the sliding direction near the surface become stress concentrators and initiate wear-particle formation.