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 test machine at room temperature. The tangential coefficient φ 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 wear coefficient K obtained was on the order of 10^-7 -10^-3. The wear coefficient increased with increasing tangential coefficient and increasing slip ratio. The observed drastic change of wear coefficient related closely to the change of microscopic wear mode which was evident by the inspection of the wear surface with an SEM. When S>10%, the wear surface became very rough and showed many cracks and marks of deramination of flakes, and K was larger than 10^-5. When S<10% and φ >0.3, wear surface showed partial fracture on a scale similar to the pore size, and K was 10^-6 order. When S<10% and φ <0.3, wear surface remained initial pores clearly and crack was not observed, and K was less than 10^-6.