Effects of nitrogen flow ratio on the mechanical and anticorrosive properties of cosputtered (TiZrHfTa)Nx films

In this study, TiZrHfTa films were cosputtered through cyclical gradient composition deposition by using four single-element targets connected to direct-current power supplies. Multilayered and columnar structures formed at low and high rotation speeds of the substrate holder (RH), respectively. (TiZrHfTa)Nx thin films were then prepared through reactive cosputtering by using Ar/N2 mixed gas. A high RH value resulted in these films having homogeneous structures. Without the addition of reactive nitrogen gas, the fabricated metallic Ti0.24Zr0.23Hf0.27Ta0.26 film exhibited a valence electron concentration of 4.26, which resulted in the formation of a body-centered cubic (bcc) phase; a hardness of 4.7 GPa; and an elastic modulus of 104 GPa. (TiZrHfTa)Nx films with stoichiometric ratios (x) ranging from 0.59 to 0.97 were obtained by adjusting the reactive gas ratio fN2 (N2/(N2 + Ar)) from 0.1 to 0.7. The introduction of N into the TiZrHfTa crystallites caused the bcc phase to transform into a face-centered cubic phase and enhanced the mechanical properties of the films, with their hardness and elastic modulus increasing to 13.8–25.5 and 235–290 GPa, respectively. Nanoindentation, scratch, Rockwell-C adhesion, and potentiodynamic polarization tests indicated that among the prepared (TiZrHfTa)Nx films, the (Ti0.17Zr0.25Hf0.20Ta0.38)N0.75 film exhibited the best mechanical and anticorrosive properties. Target poisoning accompanied by defect formation affected the mechanical properties of the (TiZrHfTa)Nx films. The anticorrosive properties of the (TiZrHfTa)Nx films were dominated by the high-entropy effect through alloying with Ta and the adhesion strength between the films and substrates.