Tribological evaluation of self-lubricating sintered steels

Abstract

A new processing route to promote the in situ generation of solid lubricant particles has been presented recently. This route takes an advantage of a powder injection moulding process combined with a plasma-assisted debinding and sintering process (PADS). Graphite nodules were generated in situ in the volume of sintered steels during sintering simply by the dissociation of silicon carbide (SiC) particles, which were mixed into the metallic matrix powders before injection. In this work, we present and discuss the effect of the sintering temperature (1100, 1150 and 1200°C) and SiC content (0–5wt%) on the tribological behaviour (friction coefficients and wear rates of specimens and counter bodies) of these new materials. The tribological behaviour was analysed using linear reciprocating sliding tests (constant load of 7N, 60min duration). It was shown that the presence of graphite nodules significantly reduced the friction coefficients and wear rates, whereas the sintering temperature hardly affected these parameters. The results were compared with those caused by other forms of graphite (nodules in nodular cast iron and powder graphite) and were discussed in terms of the crystalline structure of the analysed graphite using micro-Raman spectroscopy. Chemical analyses of the wear scars using scanning electron microscopy (SEM–EDX) and Auger electron spectroscopy (AES) showed a tribolayer that was composed predominantly of carbon and oxygen. This tribolayer is removed and restored during sliding and is continuously replenished with graphite. Analyses of the wear scars showed traces of plastic deformation on both samples and counter-bodies and the predominance of abrasion as the main wear mechanism.