Rolling contact fatigue performance of HIPed Si3N4 with different surface roughness

Accelerated rolling contact fatigue four-ball tests were performed on hot isostatically pressed (HIPed) silicon nitride/steel contacts under lubricated condition using a PLINT TE92/HS microprocessor controlled rotary tribometer at a maximum compressive stress of 6.58 GPa and at a speed of 10,000 rpm for 135–200 million stress cycles. Rolling track surfaces were examined by optical microscopy, SEM, 3-D surface analysis, atomic force microscopy and interference profilometry. Experimental results show that with an initial roughness value Ra from 0.016 to 0.094 μm, the surfaces became smoother during testing and surface pitting (10–20 μm) occurred. For the surfaces with a roughness value Ra from 0.002 to 0.008 μm, the surfaces became rougher and lubricant oil residues were deposited at the edges of rolling track. Some small and shallow surface pitting 2–3 μm in size was also observed. Some scratch marks left on the surface by the previous lapping process were further extended during testing. Ra and Rq are still most important roughness parameters in relation to rolling contact behaviour. The effects of other surface roughness parameters, such as the shape of the valley, Rsk and Rku are not obvious in this study.