Friction and wear of self-lubricating composites at temperatures to 450 °C in vacuum

Abstract The tribological characteristics of hot-pressed self-lubricating composites, consisting of molybdenum disulfide, refractory metal oxides and refractory metals, were evaluated at temperatures up to 450 °C in vacuum. Sliding bearings made from the composites were run against 304 stainless steel shafts at a rotational speed of 120 rev min −1 under an applied load of 1.7 N for (6–10) ×10 6 revolutions. Wear was negligible at temperatures under 100 °C. However, wear of the composite bearings, at a specific wear rate of (2–5) ×10 −8 mm 3 N −1 mm −1 , occurred at 300 °C. At 450 °C, a weight loss of about 10–30 mg of the shaft and a weight gain of almost the same amount of the bearings were observed. X-ray photoelectron spectroscopy analysis revealed iron and traces of iron sulfide on the bearing surface, indicating that a chemical reaction had occurred between the composite bearing and the steel shaft. To examine the effect of counterpart material, pin-on-disk friction tests using a composite pin and an Si 3 N 4 disk were performed at temperatures up to 450 °C. In contrast to the 304 steel counterpart, an excellent tribological response was found with the Si 3 N 4 disk. The specific wear rate of the composite pin at 450 °C was 2.2 × 10 −10 mm 3 N −1 mm −1 and the wear of the Si 3 N 4 disk was negligible. An attempt was made to improve the strength of the composite. By adding 304 stainless steel in a fraction of 5% to the composition, an improvement in strength of the composite of about 30% was obtained. Furthermore, this had a good effect on the tribological performance of the composite at high temperature.