Composition and Microstructural Design for Improved Wear Properties in Sialon Ceramics

The wear properties of a series of sialon ceramic materials have been studied under dry sliding conditions through block on ring wear tests. Compositional effects were studied by producing materials with different rare earth oxides as the stabilizing element in the a phase. The effects of microstructure on the wear properties were studied by producing two-phase a / β composite materials in which the β phase exists with an elongated grain morphology. Under high load wear conditions where wear occurred by fracture following intergranular microcracking, the microstructure plays a significant role in wear with the elongated microstructures of the composites producing lower wear volumes. However under low load conditions where tribochemical type wear is thought to be dominant, the improved chemical stability of the single-phase materials provided better wear resistance. Under these conditions there was a larger effect of rare earth species, with smaller, more refractory rare earths providing better wear resistance. These results showed a trade off type behaviour between materials suitable for high and low load wear conditions and resulted in a strategy of designing materials where the elongated microstructures required for high load wear resistance were developed in the a phase thus retaining the low load tribochemical wear resistance.