Chemical wear of sintered Si 3N 4, hBN and Si 3N 4–hBN composites by water lubrication

Abstract

Chemical/mechanical wear ratios of Si 3N 4, hBN and Si 3N 4–hBN composites were investigated by determining the quantity of ammonia tribochemically produced in water. Chemical wear ratio, defined as an index of the chemical contribution to wear, showed a high value in the low-wear region and was expressed in an exponential curve as a function of the total wear loss. The chemical wear ratio of Si 3N 4 depended strongly on sliding speed, but negligibly on surface roughness. A large constant for the k a of the regression curve of the chemical wear ratio showed a large chemical contribution to the wear of the material. A high constant k a=17 was observed for Si 3N 4 and low value of 8 for hBN indicated that wear proceed mainly mechanically. These results indicate that wear proceed chemically in the region of low wear rate, and a high chemical wear was observed on mechanically strong material. The Si 3N 4–hBN composite also showed a high chemical wear ratio in the low wear region, the curve of which is expressed by the linear combination of the equations for Si 3N 4 with hBN. Furthermore, a chart of chemical wear ratio as a function of total wear loss, which indicates the chemical contribution to the wear of a material, is presented for practical use as a chemical wear map.