SLIDING FRICTION AND WEAR UP TO 600-DEGREES-C OF HIGH-SPEED STEELS AND SILICON NITRIDES FOR GAS-TURBINE BEARINGS

The sliding friction coefficients and specific wear rates of a range of differently processed (sintered and wrought) high speed steels and (hot isostatically pressed, hot pressed and sintered) silicon nitrides have been measured in both dry and boundary lubricated conditions at temperatures from 20 to 600-degrees-C (dry) or 200-degrees-C (lubricated). In dry conditions, the wear of high speed steels and silicon nitrides on themselves was similar up to 400-degrees-C, rising from 5 X 10(-9) mm3 mm-1 N-1 at 20-degrees-C to 5 X 10(-8) mm3 mm-1 N-1. However, in the range 400-600-degrees-C, the wear rates of the silicon nitrides continued to rise, while those of the tungsten high speed steels stayed constant and those of the molybdenum steels decreased. There was no effect of processing route. The boundary lubricated testing was carried out under a synthetic ester with and without a zinc dithiophosphate (ZDDP) additive. For all the materials, the specific wear rates were in the range 10(-11)-10(-10) mm3 mm-1 N-1 but these rates were near the measurement limit and running-in was still progressing over the 1 to 2 km sliding distance of the tests. A small amount of dry testing has been performed with silicon nitride sliding on high speed steel and on alumina and these results also are reported. A characteristic of all the dry testing was the formation of surface films from which the wear debris was formed. This perhaps explains the lack of any processing route effect.