WEAR TRANSITION DIAGRAM FOR SILICON-CARBIDE

To obtain information on the tribological behaviour of silicon carbide at elevated temperatures, unlubricated ball-on-flat wear tests were c onducted on sintered silicon carbide in self-mated sliding in air. The contact load was varied from 3.2 to 98.0 N, and a temperature range o f 23 degrees C to 1000 degrees C was used. Scanning electron microscop y, Fourier transform infrared spectroscopy and energy-dispersive spect roscopy were used to elucidate the wear mechanisms. The results of the tests and observations were employed to construct a wear transition d iagram, which provides a summary of tribological information including friction coefficient, wear coefficient and wear mechanisms as a funct ion of temperature and load. The wear transition diagram for the sinte red silicon carbide studied is divided into four regions plus one tran sition zone. At room temperature, under high loads and high environmen tal humidity, the tribological behaviour is controlled by tribochemica l reactions between the silicon carbide surface and water vapour in th e environment. Under low loads and at temperatures below 250 degrees C , wear occurs by ploughing and polishing. At temperatures about 250 de grees C and under low loads, tribo-oxidation and formation of cylindri cal wear particles control the tribological behaviour. Wear occurs by microfracture when the load is increased above a critical value; and b oth the friction coefficient and the wear coefficient increase.