The friction and wear of thin titanium nitride and silicon nitride coatings on stainless steel at temperatures to 500 °C

Abstract

An investigation has been undertaken into the friction and wear behaviour of thin ceramic coatings on 321 stainless steel specimens in carbon dioxide during like-on-like reciprocating sliding at 20–500 °C. In particular, comparisons have been made between an adherent titanium nitride coating on a relatively smooth stainless steel substrate, an adherent titanium nitride coating on a harder, relatively rough chromized stainless steel substrate and a poorly adherent silicon nitride coating on a smooth stainless steel substrate.During sliding at 20° and 300 °C, the presence of the titanium nitride coating caused considerable reductions in the friction and wear rate for the stainless steel specimens, by eliminating metal-to-metal contact. However, the coating was thinned progressively until, eventually, particularly at the higher temperature, it was unable to prevent such contact and the friction and wear rate increased significantly. At 500 °C, a wear-protective oxide glaze developed on the uncoated steel specimens after some time, giving relatively low friction and wear rates. The presence of the coating protected the steel in the early stages while oxidation of the coating and of any exposed alloy substrate ensured that a low wear rate was maintained for long periods.The titanium nitride coating was much less effective on the chromized steel substrate, owing to the presence of surface asperities which were significantly higher than the coating thickness. These caused rapid removal of the coating during sliding. Likewise, poor adhesion between the silicon nitride coating and the stainless steel substrate enabled the coating to be stripped very quickly at all temperatures and the friction and wear rates were found to be comparable with those of the corresponding uncoated system.