DYNAMIC RECRYSTALLIZATION DURING THE SLIDING WEAR OF ALUMINA AT ELEVATED-TEMPERATURES

In previous studies, a very fine grain size surface layer of several m icrometer thickness has been consistently observed in the wear track o f alumina couples after wear at elevated temperatures, Detailed micros tructural observations have revealed that dynamic recrystallization is the most probable mechanism for the surface layer formation, In this study, grain size and thickness of the surface layer are reported for the samples tested under various wear conditions, Both the grain size and the thickness are dependent on the testing temperature, nominal co ntact pressure, and the sliding velocity, The strain rate and the loca l temperature of the wear surface are estimated taking frictional heat into account and the Zener-Hollomon parameter Z = epsilon exp(Q/RT) i s calculated, A logarithmic plot of the grain size and Z yields a good linear relationship, This linearity and the slope of -0.21, similar t o that previously reported for metals, further substantiate that dynam ic recrystallization occurring in the wear surface is responsible for the formation of the fine grain size surface layer.