Tribological behaviour of plasma-sprayed chromium oxide coating

A plasma-sprayed chromium oxide coating was studied to gain a better understanding of its tribological behaviour. Both dry and lubricated wear tests were conducted with a reciprocating motion at room temperature and at 450°C for the dry wear tests, and at room temperature and 200°C for the lubricated wear tests. Under dry sliding conditions, dispersed smooth surface films were formed by plastic deformation of compacted debris particles that adhered to the surface and these films strongly influence the friction coefficient and wear rate of the coating. Considerable quantity of CrO 3 was detected at room temperature whereas CrO 2 was detected at 450°C. CrO 2 in the smooth film seems more favorable than CrO 3 in reducing friction. Under lubricated sliding conditions, tribochemical reaction films of different species of carbon–oxygen bond units were formed depending on the test temperature. The surface films appear to be effective in reducing friction and preventing wear. The dominant species with carbon-associated bonds in the film was identified as graphite at both room temperature and high temperature. Among the compounds formed in the film, graphite appears to be most important in determining the tribological performance of the film.