Effect of Substrate Bias on the Microstructure and Properties of Non-Equimolar (AlCrSiTiZr)N Films with Different Cr/Zr Ratios Deposited Using Reactive Direct Current Magnetron Sputtering

Abstract

To reduce the cost of tools operated in extreme environments, we developed films with excellent corrosion/oxidation resistance. Two high-entropy nitride films, (AlCrSi0.3TiZr)N and (AlCr1.5Si0.3TiZr0.5)N, were deposited using reactive DC magnetron sputtering under different substrate biases. The films exhibited a maximum hardness of 32.5 GPa ((AlCrSi0.3TiZr)N) and 35.3 GPa ((AlCr1.5Si0.3TiZr0.5)N) when deposited at −150 V, corresponding to 27 and 142% increases compared to those deposited at 0 V. This indicates that the bias strengthened (AlCr1.5Si0.3TiZr0.5)N (higher Cr/Zr ratio) more significantly. The enhancement of the mechanical properties was highly correlated with the interstitial point defects and densification of the film microstructures. The corrosion resistance of the films deposited on 6061 Al alloy substrate under different biases was tested in 0.1 M H2SO4. (AlCrSi0.3TiZr)N and (AlCr1.5Si0.3TiZr0.5)N displayed the lowest corrosion currents of 0.75 and 0.19 μA/cm2 when deposited at −100 and −150 V, respectively. These values are two orders of magnitude lower than that of the uncoated substrate. The (AlCr1.5Si0.3TiZr0.5)N film showed better oxidation resistance than the (AlCrSi0.3TiZr)N film and remained partially oxidized after heat treatment at 1000 °C. The (AlCr1.5Si0.3TiZr0.5)N film deposited at −150 V exhibits excellent mechanical properties and corrosion/oxidation resistances, making it suitable for protecting tools operating in harsh environments.