Composition, structure, and mechanical properties of (Ti–Hf)N coatings on titanium alloy

Variations of the composition, structure, and mechanical properties (hardness, elastic modulus) of (Ti–Hf)N coatings with increasing Hf content (Ti : Hf ratio) are reported. As test samples, VT6 titanium alloy plates covered by a magnetron-sputtered titanium hafnium nitride coating have been taken. To see how the coating characteristics depend on Hf content, samples with rated compositions (Ti$_{0.9}$Hf$_{0.1}$)N, (Ti$_{0.85}$Hf$_{0.15}$)N, (Ti$_{0.8}$Hf$_{0.2}$)N, and (Ti$_{0.7}$Hf$_{0.3}$)N have been studied. The surface and depth element distributions have been found, and the phase composition and the dependence of the titanium nitride lattice parameter on Hf content in the coating have been determined. The depth profiling of a coating's hardness and elastic modulus has been conducted by instrumental indentation. Hardness and elastic modulus have been found to be maximal ($\sim$35 and $\sim$500 GPa, respectively) in (Ti$_{0.85}$Hf$_{0.15}$)N and (Ti$_{0.8}$Hf$_{0.2}$)N coatings. In addition, the depth distribution of Hf in these coatings has turned out to be most uniform.