Dry friction and wear of toughened zirconias and toughened aluminas against steel

The unlubricated friction and wear behavior of toughened zirconias and toughened aluminas against hardened steel was studied using the Falex ring-and-block technique. Three experimental ZrO₂-Y₂O₃ ceramics, two commercial ZrO₂-MgO ceramics and two commercial Al₂O₃-ZrO₂ ceramics were investigated. Each ceramic was tested at 500 rev min^?1 (92 cm s^?1) and 2000 rev min^?1 (367 cm s^?1) at normal loads in the range 2.3–40.8 kgf. The materials characteristics of the ceramics before test, the features of the tested samples, and the friction and wear data are presented and related. Under mild wear conditions, all the ceramics exhibited low wear, with the ZrO₂-Y₂O₃ samples having the lowest. The wear of the toughened zirconias exhibited a strong sensitivity to sliding speed, while the toughened aluminas did not. Also, the lower toughness ceramics were susceptible to macroscale structural damage (cracking and chipping) even when the overall wear was low. Micro structural examination of a tested friction pair (ring, ceramic block and wear debris) has shown that the wear process is very complex, encompassing many mechanisms which are described. A generalized wear equation relating wear to load, sliding speed and sliding time is proposed.