Effect of Heat Treatment on the Hardness of Ti-Mo-N Coating Films Deposited by RF Reactive Magnetron Sputtering

Abstract

  Effects of heat treatment on microstructure and hardness of Ti-Mo-N coating films were investigated for various N contents. Ti-Mo-N films were deposited onto a stainless steel substrate by a reactive RF sputtering process in the mixture of argon (7.5 ccm) and nitrogen (0~2.0 ccm) gases using Ti₅₀Mo₅₀ target. X-ray results of as-deposited films indicated that the main phase of the Ti-Mo-N film was a bcc-(Ti, Mo) phase at a nitrogen flow rate (f_N2)≤0.2 ccm and a δ-(Ti, Mo)N phase at f_N2 over 0.3 ccm. The Ti-Mo-N films so obtained were heat treated in argon atmosphere at 300~1100°C for 30 minutes. Hardness was measured by a nanoindentation system. The hardness of the Ti-Mo-N films deposited at f_N2=2.0 ccm hardly changed with heat treatment. In contrast, the hardness of the films deposited at f_N2=0.2 and 0.3 ccm was drastically increased by heat treatment at temperatures higher than 900°C. In particular, the film deposited at f_N2=0.3 ccm showed the maximum hardness of about 35 GPa by heat treatment at 1000°C for 30 minutes. X-ray measurement and TEM observation indicated that the increment of hardness in the Ti-Mo-N film at f_N2=0.3 ccm is due to the formation of a bcc-(Ti, Mo) phase in a δ-(Ti, Mo)N phase.