Thermal kinetics of protective oxide layer formation in the dry sliding of metallic tribo-specimens

This article investigates the kinetics of friction-induced-heat flux within the contact layers of a rubbing solid. It is shown that nominally isotropic solids may exhibit anisotropic thermal behavior due to the mechanical dilatation exhibited during sliding. Depending on the degree of anisotropy the local flow of the thermal flux may be congested. This leads to the accumulation of thermal energy within the mechanically affected zone (MAZ) of the solid and may contribute toward a thermal environment that is conducive to protective layer formation. Depending on the evolution of mechanical dilatation, and the associated congestion of thermal flow, lateral accumulation of heat may take place. This, in turn, under favorable conditions causes the formation of a soft zone of low resistance to shear, thus leading to a transition in the mechanism of wear (e.g. from oxidative to delaminating). These effects are studied within the context of the sliding of a mild steel couple, and the results are subsequently applied to investigate the transition in the wear regime of a titanium (Ti–6Al–4V)–tool steel (AISI M2) sliding pair.