Effect of grain size on friction and sliding wear of oxide ceramics

Abstract

Microstructures of Al 2O 3 and 3mol.%Y 2O 3-ZrO 2 (TZP) with systematically varying average grain sizes were produced by sintering. The hardness and fracture toughness of the ceramics as well as the amount of tetragonal, cubic and monodinic phases of TZP-ZrO 2 were measured. Wear tests were carried out on the different self-mated microstructures in dry unidirectional and reciprocating sliding contact respectively, using block-on-ring geometries in air at ambient temperatures. The microstructures and worn surfaces were systematically analysed using scanning electron microscopy and X-ray diffraction techniques. Experimental results showed that plastic deformation, intercrystalline microfracture, grain fragmentation, surface layers and delamination fracture contributed to the friction and wear processes. The theoretical analysis of wear as a function of time or length of wear path revealed a sharp transition from a high to a low level of wear intensity with decreasing apparent surface pressure for both oxide ceramics. A transition in the wear intensity occurred also as a function of the average grain sizes. These effects were attributed to a change in wear mechanisms.