The effects of material combination and surface roughness in lubricated silicon nitride/steel rolling contact fatigue

Four kinds of commercially finished 12.7 mm HIPed silicon nitride bearing balls with surface roughness values Ra ranging from 0.002 to 0.016 μm were tested using a four-ball rolling configuration. They were rolling against two types of steel testing balls with different surface roughness and hardness, in fully lubricated condition at a maximum compressive stress of 6.58 GPa and at a speed of 10 000 rpm for over 135 million stress cycles. Rolling track surfaces were examined by microscope, SEM, 3-D surface analysis and interference profilometry. Experiment results show that the composite surface roughness are most influential. The shape of the surface topography of silicon nitride are not very sensitive. The slight difference in steel hardness may lead to significant differences in steel fatigue life.