The role of apparent contact pressure in the sliding wear of polycrystalline alumina in conformal contacts

Wear resistance of alumina and other structural ceramics is generally correlated with load due to the difficulties in estimating the contact pressure between the sliding surfaces having poor conformity. In the present work, wear and friction characteristics of high-density high-purity alumina have been studied with a flat-on-flat test configuration using a pin-on-disc type unidirectional wear testing machine, and efforts have been made to correlate the results with apparent contact pressure. The tests were conducted over a sliding distance of up to 6 km with normal loads ranging from 30 N to 50 N to obtain a nominal contact pressure of between 2.5 MPa and 8.5 MPa at the interface. Both wear and friction were found to be higher as the apparent contact pressure increased from 2.5MPa to 6MPa. At 8.5MPa, wear and friction levels were lower. Even under a constant load, the change in contact pressure exhibited different wear values, which is indicative of different wear mechanisms. Up to a contact pressure of 6 MPa, abrasive ploughing and occasional grain pull-out were the dominant features whereas at higher contact pressure (8.5 MPa), compaction of wear debris on the sliding surfaces was observed. © 2008 DVS Verlag GmbH.