Tribochemical effects on CNx films

CNx thin coatings have been deposited by dc magnetron sputtering using a graphite target in nitrogen atmosphere under different experimental conditions. X-Ray photoelectron spectroscopy, electron-energy loss spectroscopy, nuclear magnetic resonance and Fourier-transformed infrared spectroscopy were used to elucidate the structural chemistry of each film. The tribological behavior has been investigated using a reciprocating pin-on-flat tribometer in a wide range of environmental conditions: ambient air, dry air and nitrogen. Tribochemical effects in relation to the nature of the surrounding atmosphere during friction tests are presented. Strong relationships between the N/C ratio, the nature of C–N bonds and the friction behavior are highlighted and discussed. An optimum in the friction and wear properties was found for a maximum in the CN/CC ratio for the studied set of CNx samples. The XPS/AES analysis of the sliding counterfaces support a destabilization of the CNx network under friction and build-up of a carbon rich tribolayer under steady-state.