testing environment at room temperature played a minor role where the averaged steady state friction coefficient in ambient air was slightly lower ( "' 0.45) compared to Ar ( "' 0.67), although the wear rates listed in Table 2 were slightly lower in Ar. During both ambient tests, the Co-base alloy pin exhibited wear loss (Fig. 5a) while there was correspond- ing volume gain on the Ta–W flat (Fig. 5b)