Abstract

Observations of failure mechanisms of silicon nitride rolling elements in relation to surface line defects under rolling contact has been carried out. The purpose of the present investigation is to study the way in which surface line defects fatigue fails and to interpret the failure processes. The rolling contact tests are performed on silicon nitride/steel elements. A modified four-ball machine is used to carry out fatigue tests. Silicon nitride ball surfaces are examined before experimental fatigue tests using a dye-penetrant technique and light microscopy. The surfaces of during testing, post-test and failure are examined using light microscopy and electronic microscopy. Secondary surface cracks play a dominant role in the formation of spalling failure. These cracks propagate conically away from the surface and meet the path from the fatigue crack propagation originated from the pre-existing line defect, and eventually result in the formation of an ellipse fatigue spall.