Comparison of four-ball and five-ball rolling contact fatigue tests on lubricated Si3N4/steel contact

Accelerated four-ball and five-ball rolling tests were performed on HIPed Si₃N₄ ball samples (rough lapped with surface roughness value R_a 0.08 μm and R_q 0.118 μm) in fully lubricated condition. The contact load and the stress cycles per minute for four-ball rolling and five-ball rolling tests were maintained the same. The rolling track appearances of five-ball tests reveal severe sliding occurred. In one case, the opposite arc cracks were generated all over the two sides of the rolling track, and this could not be explained by simplified kinematics model. The failure mechanisms were discussed, which suggest the sliding on the two sides of the track was in the opposite direction.