Electrochemical and XPS studies of sputter-deposited ternary Mn–Ta–Cr alloys in chloride-free and chloride-containing sulphuric acid solutions

Abstract

Amorphous manganese-rich (67–80 at.%) Mn–Ta–Cr alloy films were prepared by DC magnetron sputtering method. The corrosion behavior and stability of the Mn–Ta–Cr alloy films were examined in chloride-free and -containing 1 M H 2SO 4. AC and DC electrochemical techniques in combination with XPS analysis were used. Mn–Ta–Cr alloys exhibited very high corrosion resistance and stability up to transpassive dissolution region of chromium. The high corrosion resistance of Mn–Ta–Cr sputtered films is based on the formation of double oxyhydroxide passive film composed mainly of chromium and tantalum. The partial substitution of tantalum with chromium improves the corrosion resistance of the sputter-deposited alloys via accelerating the preferential dissolution of manganese and stabilizing alloy/passive film interface. A change in the passive film structure was observed when the alloys were anodically polarized at potentials higher than 0.6 V (SCE).