Corrosion resistance of electrolessly-deposited nano-sized Ni-Mo-P alloy coatings

In this paper, first, two kinds of Ni-Mo-P alloy coatings respectively with nanocrystalline and mixed-crystalline (a mixture of amorphous and microcrystalline) structures were prepared by an electroless process. Next, single-and double-phase nanocrystalline Ni-Mo-P alloy coatings were obtained via different crystallization processes of the mix-structure counterpart. Then, die corrosion behaviors of the obtained coatings in 5% sulfuric acid solution were investigated according to the anodic polarization curves of the coatings. The results were finally compared with those of Ni-P coatings. It is shown that the as-plated nanocrystalline Ni-Mo-P coatings possess much higher corrosion resistance than the as-plated nanocrystalline Ni-P coatings, that the single-and double-phase nanocrystalline Ni-Mo-P coatings after the annealing are of better corrosion resistance than the as-plated mix-structure and nanocrystalline counterparts, and that, after the annealing, the corrosion resistance of the double-phase nanocrystalline Ni-Mo-P (Ni + Ni3P) coatings is similar to that of the single-phase counterparts.