A tentative explanation for the tribochemical effects in fretting wear

In many fretting investigations, tribochemical reactions have been reported to critically determine the wear and friction behavior, however, different and contradictory assessments of the importance of mechanical and thermal effects on these reactions have been suggested. Since fretting is character ized by relatively slow sliding speeds, high temperatures are not generated over the entire nominal contact area. However, evidence for phase transfor mations, which are typical of high temperatures, have been observed many ti mes in fretting experiments. In other words, there exists a discrepancy bet ween the macro- and micro-scale observations. In our previous experimental and theoretical work, the tribochemical transformations of steel and cerami cs were extensively investigated and the presence of very high flash contac t temperatures under gross slip fretting was confirmed. In th is paper we p resent a tentative explanation of the mechanism for the observed tribochemi cal changes under selected fretting conditions, which can also explain the discrepancy in the results from macro- and micro-scale studies. The propose d wear mechanism considers the tribochemical transformations at the asperit y spot-to-spot contacts due to high flash temperatures, while the heat gene ration and dissipation at apparent contact area remain significantly lower. The observed overall wear transition occurs due to gradual accumulation of the transformed material, which in "closed" fretting contacts remains in g reat part within the contact. (C) 2001 Elsevier Science B.V. All rights res erved.