A NEW PARAMETER FOR ASSESSMENT OF CERAMIC WEAR

Friction and wear tests were carried out on a face-loaded ring-on-ring wear tester. The materials used in this study were HIPed zirconia (Zr O2) and silicon nitride (Si3N4). Friction and wear tests were carried out at room temperature between the same materials under unlubricated conditions. It was found that the coefficient of friction of zirconia was somewhat higher than that of the silicon nitride over the range of testing conditions. Wear rate of silicon nitride was higher than that of zirconia. Worn surfaces investigated by SEM have residual surface cracks and wear particles caused by brittle fracture. It was found tha t surface cracks were initiated at the trailing edge and propagated to generate a wear particle. It was also found that ceramics have two ty pes of wear particles, small scale in the range of submicrometers to 3 mu m and large scale in the range of 10-16 mu m. Based on these resul ts, a ceramic wear model is proposed to explain the process of wear pa rticles generation. A theoretical analysis based on fracture mechanics has been conducted. A non-dimensional parameter, S-cf, is proposed to estimate the wear rate of ceramics and is defined as S-cf=P root(1+mu (2))a/K-IC S-cf is given as a function of normal pressure, fracture to ughness of materials, crack length (the degree of surface defect of ma terial) and friction coefficient in the contact region. The ceramic we ar rate, W-s, can be expressed in term of the S-cf parameter as follow s: W-s=alpha(S-cf)(beta)