Stoichiometry, phase composition, and properties of superhard nanostructured Ti–Hf–Si–N coatings obtained by deposition from high-frequency vacuum-arc discharge

Superhard nanostructured Ti–Hf–Si–N coatings (films) possessing high mechanical properties were obtained by deposition from high-frequency vacuum-arc discharge. The elemental and phase composition and morphology of the films were studied by a combination of methods including RBS, SIMS, GDMS, SEM-EDXS, XRD and nanoindentation techniques at various pressures and bias voltages applied to the coated samples. It is established that, as the average grain size in nc-(Ti,Hf)N (nanocrystalline) coatings decreases from 6.7 to 5 nm and $\alpha$-Si$_3$N$_4$ (amophous or quasi-amorphous phase) interlayers are formed between the nanograins, the nanohardness of coatings increases from 42.7 to 48.4–1.6 GPa. However, the further grain refinement of nc-(Ti,Hf)N to 4.0 nm leads to a slight decrease in the nanohardness. The stoichiometry of the coatings changes from (Ti$_{25}$–Hf$_{12.5}$–Si$_{12.5}$)N$_{50}$ to (Ti$_{28}$–Hf$_{18}$–Si$_9$)N$_{45}$, which is accompanied by variation of the lattice parameter of (Ti,Hf)N solid solution grains.