THE COMBINED EFFECT OF SPEED AND HUMIDITY ON THE WEAR AND FRICTION OF SILICON-NITRIDE

A series of ball-on-ring wear tests was performed on sintered silicon nitride. The experiments were carried out to investigate a discrepancy in the literature on the effect of humidity on the wear of silicon nitride. In the experiments reported here, a range of different testing speeds was used and the humidity of the tests held at less than 5% relative humidity (RH), 50% (RH), or 90% (RH). It was found that at the lowest speed that was used, the wear rate at low humidity was higher than that for higher humidity. As the speed increased there was a maximum in the wear rate for the high humidity tests, and a minimum for the low humidity tests, with wear rates for the low humidity tests much lower than for the high humidity tests. At high speeds, the wear rate for the low humidity tests was much lower than that for the high humidity tests. The main mechanism of wear was the tribochemical oxidation of the silicon nitride to form silicon oxide.