THE TRANSITION FROM MILD TO SEVERE WEAR IN ALUMINA DURING SLIDING

The occurrence of a wear transition in alumina during sliding has been investigated experimentally. The results show that a transition from initially mild wear to severe wear occurs abruptly, but only after a defined period of initial wear. The time required for this transition increases with decreasing grain size and decreasing applied load. Examination of wear samples revealed that, during the initial stage, surface material is removed by a plastic grooving process and is accompanied by the accumulation of subsurface dislocations arrays and twins. With continued sliding, internal stresses associated with this accumulating damage eventually results in grain boundary cracking and grain pull-out, which leads to the onset of fracture dominated, severe wear.