THE WEAR MECHANISM OF SILICON-NITRIDE IN ROLLING SLIDING CONTACT

The microscopic wear mechanism of silicon nitride in unlubricated rolling-sliding contact was investigated by using a ring-on-ring-type test machine at room temperature. The tangential coefficient-phi was changed from 0.04 to 0.89 and the slip ratio S was changed from 0% to 100% by changing the combination of contact stress and shear stress. With these conditions the value of the wear coefficient K obtained was of the order of 10(-7) to 10(-3). The wear coefficient increases with increasing tangential coefficient and increasing slip ratio. The observed drastic change in wear coefficient related closely to the change in microscopic wear mode, which was evident by inspection of the wear surface with a scanning electron microscope. For S > 10% the wear surface became very rough and showed many cracks and marks of delamination of flakes, and K was larger than 10(-5). For S < 10% and phi > 0.3 the wear surface showed partial fracture on a scale similar to the pore size and K was of the order of 10(-6). For S < 10% and phi < 0.3 the wear surface clearly retained the initial pores, cracking was not observed and K was less than 10(-6).