Tribological reactions generated on ceramic-stellite couples contaminated by SiO₂ particles

Stellite alloy to ceramic wear experiments were carried out on a test machine by means of a vanes-on-disk apparatus in which a disk specimen was pressed against three stationary vanes. This set-up was employed to investigate three-body abrasion of a Stellite disk against Si₃N₄ vanes, using SiO₂ powder as the abrasive. The thermal effect on tribological behavior is evaluated in terms of wear loss, friction coefficient, wear mechanisms and the oxides generated at various operating temperatures. The role of SiO₂ particles indicates that they have little influence on lowering the friction coefficient, but demonstrates an effect on wear. The experimental results show that wear loss is obviously related to the wear mechanisms exhibited at different temperatures, while the friction coefficient is dependent upon the oxide species and their quantity present in the wear process as well as the hardness of the Stellite, which varies with the specimen's operating temperature. Larger wear loss always results from the wear mechanism with cracking and/or surface delamination, while smaller wear loss is associated with surface grooving. The oxides of nickel and cobalt, which prevail at low temperatures but readily become unstable at high temperatures, favor a lower friction coefficient; the oxides of silicon and chromium, which tend to appear at high temperatures, do not favor a reduction in the friction coefficient. The SiO₂ particles which get into the Stellite specimen at high temperatures can greatly improve wear the resistance.