Influence of humidity and doping elements on the friction and wear of SiC in unlubricated sliding

In this study, the effects of relative humidity and doping elements are highlighted on the friction and wear properties of SiC in unlubricated condition. At higher humidity, the friction coefficient values (~0.25) are low and are independent of doping elements. The effect of doping (varying from 400 to 3000 ppm) is more pronounced at lower humidity and the friction coefficient values decrease (as compared to undoped SiC) with the addition of Al, Mg or P. The specific wear rate is lower at the higher humidity (60% RH) as compared to the lower humidity (i.e. at 30% RH) values. As the relative humidity increases from 30% to 60%, the wear mechanism gradually changes from mechanical to tribochemical. The tribo-layer consisting of carbon and hydrated silica progressively smears with relative humidity and becomes instrumental in controlling the friction and wear properties. Finally, the formation of large needle-like debris is elucidated through SEM observations.