Microstructure and corrosion performance of CoCrFeNiSix coatings deposited by magnetron sputtering at various negative bias voltages

In this work, CoCrFeNiSix coatings were fabricated by magnetron sputtering at the negative bias voltage ranging from 0 to 100 V. The effect of negative bias voltage on the composition, microstructure and corrosion performance was studied. The results show that all CoCrFeNiSix coatings consisted of amorphous and nanocrystalline FCC phases. However, the ratio of both amorphous/nanocrystalline phases and Si/(Co + Cr + Fe + Ni) atoms decreased with increasing negative bias voltage. Applying negative bias voltage also led to the improved surface quality. Accordingly, the corrosion rate of CoCrFeNiSix coatings in 0.5 mol/L H2SO4 solution exhibited a decreasing trend. Meanwhile, the CoCrFeNiSix coating deposited at 100 V had the lowest passive current density, highest coating resistance and lowest carrier density. This was because that Si competed with Cr to suppress the formation of Cr2O3 in the compact inner layer, and thus the decreasing Si content caused by increasing negative bias voltage led to the improved protection effect of the passive film.