Effect of bias voltage on the structure and properties of CuNiTiNbCr dual-phase high entropy alloy films

The dual-phase structure has been proved to overcome the effect of strength-ductility trade-off of high-entropy alloys. However, most of the high entropy alloy films with larger atomic size difference tend to form a single amorphous structure under non-equilibrium deposition conditions such as magnetron sputtering. In this study, the dual-phase CuNiTiNbCr high entropy alloy film containing the Cu-rich FCC alloy phase and amorphous phase were synthesized by high-power pulsed magnetron sputtering at different bias voltages. The poor affinity of copper with other elements led to the segregation and enrichment of copper to form a Cu-rich FCC phase. The effects of substrate bias voltage on the microstructure, mechanical and corrosion properties of the films were investigated. With the increase of bias voltage, the content of copper in the film decreased, the stress state of the film changed significantly, and the compactness of the structure was improved. The hardness of all films was higher than that of most other high entropy alloy film systems. The films deposited under low bias voltage have better toughness. The film deposited at －50 V showed the best wear resistance due to a combination of high hardness and good toughness. The film deposited at －150 V showed the best corrosion resistance since it had the lowest self-corrosion current density (6.1 ×10−8 A/cm2), which was due to its compact structure and lower impurity content.