Materials failure mechanisms of hybrid ball bearings with silicon nitride balls

A modified Shell four-ball apparatus was used to determine failure mechanisms and estimate time to failure of hybrid ball bearings using silicon nitride and zirconia balls. The machine was set up to hold a hybrid bearing containing three ceramic balls, instead of the usual 14 in order to increase contact pressure. Five kinds of silicon nitride ceramics, which differed in terms of surface roughness, porosity as well as the amount and chemical composition of additives were investigated. The goal of this study was to establish a quality criterion for silicon nitride for industrial use in hybrid ball bearings. Lifetime and failure mechanisms varied between the five bearings with silicon nitride balls and a dependance was found on the porosity and chemical composition of the materials, whereas surface roughness did not seem to influence their performance.