Effect of temperature on the strain induced γ → ɛ phase transformation in Stellite 21 during wear test

The aim of the present work was to elucidate the influence of temperature on the wear properties, strain induced phase transformation of Stellite 21 at the temperature range of RT to 550 °C. In this purpose, a high temperature pin-on-disk tribotester equipped with a coefficient of friction data collector was used. The worn surfaces were investigated by XRD and SEM. The results showed that the coefficient of friction is minimum and has less fluctuation at room temperature. It is maxima at 200 °C and then decreases as the temperature increases. Structural analysis revealed that γ(fcc) → ɛ(hcp) strain induced phase transformation (SIT) occurs at the studied temperatures which lead to the orientation of (0 0 0 1) basal planes parallel to worn tracks. This transformation and the formation of a glaze layer (compact oxidized wear debris layer) at elevated temperatures cause lower weight-loss, minor coefficient of friction and fluctuation.