The influence of counterface materials and humidity on the tribological behavior of arc ion plated TiN films

TiN films were deposited onto AISI D2 steels by an arc ion plating (AIP) technique. The effects of atmospheric humidity and counterface materials on the tribological behavior of the AIP-TiN layer have been investigated using a conventional ball-on-disc wear apparatus. In the case of a steel counterface, the average friction coefficient increased with increasing relative humidity due to tribochemical interaction of the steel with moisture. At low relative humidity (2% RH) condition, the TiN coating layer rather gained mass due to the seizure of steel on the layer without the tribochemical reaction. For the higher humidity condition above 25% RH, the mass loss of the TiN coating layer occurred and was accelerated with the increase of the relative humidity as the tribochemical reaction was progressively dominant. In the case of the alumina counterface, the friction coefficient decreased with increasing relative humidity from 2% RH to 25% RH. This behavior was explained by the formation of the aluminum–hydrated oxide phase between counterface materials. On the other hand, the increasing relative humidity up to 85% RH induced a large increase of both average friction coefficient and its deviation, in addition, increased the wear rates of both counterface layers. This behavior was explained with the accelerated fracture of the alumina ball due to the reduced flexural strength in moist conditions.