Corrosion resistance of ternary NiP based alloys in sulfuric acid solutions

NiP based alloy films were prepared by autocatalytic deposition and their structure, chemistry and corrosion behaviors in sulfuric acid solutions were studied as a function of their composition. The as-prepared Ni-based alloys are nanocrystalline, and their grain size decreases with increasing P content. Addition of a third element (W or Mo) influences the observed grain size. At low anodic overpotential NiP based alloys present a lower exchange current and lower reactivity than Ni, both improving with increasing P content. Contrary to Ni however, the NiP based alloys do not passivate at higher anodic overpotentials. Addition of W to NiP alloys can improve their corrosion resistance, while addition of Mo has little or no beneficial effects on corrosion properties.