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 R-a from 0.016 to 0.094 mum, the surfaces became smoother during testing and surface pitting (10-20 mum) occurred. For the surfaces with a roughness value R-a from 0.002 to 0.008 mum, the surfaces became rougher and lubricant oil residues were deposited at the edges of rolling track. Some small and shallow surface pitting 2-3 mum in size was also observed. Some scratch marks left on the surface by the previous lapping process were further extended during testing. R-a and R-q 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. R-sk and R-ku are not obvious in this study. (C) 2001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.