On the influence of tribo-induced superheating on protective layer formation in dry sliding of metallic pairs

This paper studies the effects of the heat diffusion ability of a rubbing material on wear resistance at high temperatures. These effects are studied with a special focus on the dilution of thermal energy in sliding. The results suggest a correlation between wear transition and the change in the heat transfer limit of a rubbing material. The nature of change in the thermal properties before and after the transition influences the thermal environment within the contacting layers. This controls the kinetics of oxide formation and thereby controls wear. Thermal dilution is a super position of three functions which represent the competing effects of the room temperature thermal properties and their respective variation with temperature. Hence, the change in the thermal properties bears on dilution. The possible relation between thermal dilution and protective oxide formation is studied by examining fretting wear data for two alloys: a Ni-based alloy and a Go-based alloy. Results indicate a strong correlation between the formation of protective oxides and the change in the dilution of thermal energy of the examined alloys with temperature. Moreover, examination of the wear data suggests that a critical ratio between the effects of the conductivity and those of the diffusivity has to be established for favorable wear resistance. This ratio reflects on the intrinsic ability of the material to sustain an oxidative reaction of a controlled rate in which protective glaze oxide layers are formed in a rate that is approximately equal to the rate of oxide layer break down. Therefore, continuous compensation for the removed oxide layer (self-repairing oxides) is established in such a case. (C) 2001 Editions scientifiques et medicales Elsevier SAS.