Corrosion resistance of electrolessly deposited Ni–P and Ni–W–P alloys with various structures

As-plated binary Ni–P and ternary Ni–W–P alloy films with either nanocrystalline, amorphous or mixture of nanocrystalline and amorphous (denoted as mix-structure) structures were prepared by electroless deposition. Single-phase nanocrystalline Ni–P and Ni–W–P alloys were also synthesized by crystallization of their mix-structure counterparts. Corrosion behaviors of the obtained deposits in a 0.5 M sulfuric acid solution were investigated. It was found that the as-plated nanocrystalline deposits, whether the binary Ni–P or the ternary Ni–W–P ones, and the annealed binary Ni–P alloy films, all possessed a corrosion resistance much lower than that of their amorphous counterparts. The annealed ternary Ni–W–P alloys, however, had a corrosion resistance higher than that of their amorphous counterpart. This result was attributed to the formation of a dense tungsten oxide film on the surface during annealing process, which was favored strongly by the high density diffusion paths provided by the large fraction of grain boundaries present in the nanocrystalline deposits.