Scratch Deformation Behaviour of Alumina under a Sharp Indenter

To understand the roles of grain size and a small amount of glassy phase in the abrasive wear mechanisms of brittle ceramics, controlled single-pass scratch experiments were conducted with a Vickers diamond indenter on a range of pure, polycrystalline aluminas of varying grain size (1-25 μm) as well as on a commercial, 10 vol% glass containing alumina (AD90). These tests were made at a constant speed of 0.36 m min ¹ under a wide range of normal loads, P (≅ 0.05-20 N). The tangential frictional force, width and depth (and hence wear volume) of the groove all increased with the normal load. The wear volume of 1 μm alumina was about an order of magnitude smaller than those of 5-25 μm grain size pure, polycrystalline aluminas. However, at P >10 N the wear volume of AD90 was the smallest of all aluminas examined. These observations of a strong grain size effect and considerable influence of glassy phase in the abrasive wear behaviour of alumina are discussed in terms of residual stress intensity factor and scanning electron microscopic evidence of a wear mechanism controlled predominantly by grain boundary microfracture.