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

Abstract

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 (R-H), respectively. (TiZrHfTa)N-x thin films were then prepared through reactive cosputtering by using Ar/N-2 mixed gas. A high R-H 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)N-x films with stoichiometric ratios (x) ranging from 0.59 to 0.97 were obtained by adjusting the reactive gas ratio f(N2) (N-2/(N-2 + 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)N-x films, the (Ti0.17Zr0.25Hf0.20Ta0.38)N-0.75 film exhibited the best mechanical and anticorrosive properties. Target poisoning accompanied by defect formation affected the mechanical properties of the (TiZrHfTa)N-x films. The anticorrosive properties of the (TiZrHfTa)N-x films were dominated by the high-entropy effect through alloying with Ta and the adhesion strength between the films and substrates.