Hardness and wear properties of Ti-Mo-C-N film

The hardness and wear properties of Ti-Mo-C-N films were investigated by nanoindentation and ball-on-disc measurements, respectively. Ti-Mo-C-N films were deposited onto a stainless steel substrate by a reactive RF magnetron sputtering in the mixture of argon (7.5 ccm) and nitrogen (0-6.0 ccm) gases using Ti₂₅Mo₂₅C₅₀ target. Ti-Mo-C film deposited without nitrogen gas flow showed a hardness of 34.8 GPa. The hardness drastically decreased with increasing nitrogen gas flow rate (/n2) and reached to a minimum hardness of 16.4 GPa at fN₂=2.0 ccm. Contrarily, at overf N₂=3;0 ccm, the hardness drastically increased with increasingf N₂ and reached a maximal value of 32 GPa, and then slightly decreased again with further increase of fn₂. It was found by TEM observation that the drastic decrease in hardness is caused by the formation of nanocrystalline microstructure, while the increase in hardness is due to the microstructural change from nanocrystalline to columner structure. The friction coefficient decreased with increasing fn₂ and the film deposited at fN₂=5.0 ccm showed a minimum value of 0.27. The simple oxidation test in air indicated that lubricious M0O₃ is easy to be formed in the film deposited at a high/N₂, which should cause the reduction of friction coefficient.