The Influence of natural surface defects on rolling contact fatigue failure modes of HIPed Si3N4

Three kinds of surface crack type defects (star defects, grinding defects and C-crack defects) on Hot Isostatically Pressed (HIPed) silicon nitride rolling elements were characterised under dye-penetrant and UV light, microscopy inspection. These surface defects were naturally formed during the finishing process not artificially induced. They were positioned to the rolling track and accelerated Rolling Contact Fatigue (RCF) tests we conducted at a maximum contact stress of 6.58 GPa and 10,000 rpm in fully, lubricated condition under 4-ball rolling configuration. The experimental results suggested that these defects can lead to fatigue spall failure,. the crack propagation from underneath the surface to the surface face is fast, and the failure time may be related to the initial crack depth