Effect of load on the friction and wear characteristics of Si3N4-hBN ceramic composites sliding against steels

The tribological behaviors of Si3N4-hBN ceramic composites sliding against steels (austenitic stainless steel (ASS) and 45 steel) under dry friction conditions at different loads were investigated by using an MMW-1 type vertical universal friction and wear tester. The experimental results showed that the friction coefficients and wear rates first showed a decrease and then an increase with an increase in the load under dry friction conditions. The better tribological performance was exhibited by the SN10/ASS sliding pair under a load of 20 N (the friction coefficient was as low as 0.27 and the wear rates of both pin and disc had a magnitude of 10−6 mm3 N−1 m−1). This may be attributed to the formation of a black surface film (consisting of B2O3, SiO2, and Fe2O3). For the same sliding pair, when the load was 10 N, the dominating wear mechanism was abrasive wear. Hence, the friction coefficient was higher (0.7). When the load increased to 30 and 50 N, the wear mechanism of the SN10/ASS sliding pair was a combination of abrasive and adhesive wears, and higher friction coefficients (0.48 and 0.72 under loads of 30 and 50 N, respectively) were obtained. On the other hand, the contents of hBN also showed a significant impact on the tribological behaviors of the Si3N4-hBN/ASS sliding pairs. When the hBN content was less than 10%, the friction coefficients of the Si3N4-hBN/ASS sliding pairs decreased with an increase in the hBN content. On the other hand, at hBN contents of 10% or more, the friction coefficients of the sliding pairs increased with an increase in the hBN content. Under the same experimental conditions, the Si3N4-hBN/45 steel pairs showed poor tribological properties as compared with the Si3N4-hBN/ASS pairs.