High temperature phase transformations under fretting conditions

Different and sometimes contradictory assessments of the importance of thermal and mechanical effects on tribochemical reactions in fretting have been reported in the literature. In our study of fretting wear between steel and silicon nitride ceramics, tribochemical reactions were determined to play the critical role under both non-lubricated and oil-lubricated conditions. Various possible effects on the resulting tribological interfaces are discussed based on the experimental evidence of microstructural changes, phase transformations, various thermodynamic and flash temperature calculations, and interaction couple experiments in which chemical wear was isolated by controlled mechanical and thermal parameters. It is shown here that a very high temperature must be considered as the most important factor influencing in tribochemical reactions and various phase transformations, even under conditions which are usually considered to be low speed–low temperature conditions.