Wear mechanisms of silicon nitride bearing materials under contact fatigue stresses

The objective of this research was to investigate wear mechanisms of silicon nitride as bearing elements. The study is focused on two questions: (1) How does Si{dollar}sb3{dollar}N{dollar}sb4{dollar} wear initiate and develop in the hybrid ball bearing system? (2) What materials and mechanical factors control wear initiation and development? The properties and fracture behavior of advanced silicon nitride bearing material, such as toughness, crack initiation and propagation, R-curve behavior, cyclic fatigue resistance, subcritical crack growth, and fractography, have been studied. The ball-on-disc cyclic-fatigue testing method has been successfully designed and applied to simulate loading conditions in a hybrid ball-bearing operation. The diametral compression test has been used to study crack growth mechanisms and environmental influence on crack growth. The AFM, SEM, and XPS are the primary techniques that were used to study the topography and chemistry of the fracture and wear surfaces. From this research, wear mechanism models for Si{dollar}sb3{dollar}N{dollar}sb4{dollar} bearing materials have been established. The causes of the wear have been determined to be directly related to a mode I brittle fracture process. The results of this research will lead to improvement in silicon nitride wear resistance by adjustment of the microstructure.