Morphology and High-Temperature Oxidation Resistance of Amorphous Ni-W-P Alloy Coatings

Ni-W-P alloy coatings with high content of W and different contents of P whose atom fractions were 0, 2.1%, 3.9%, 4.6%, 8.8%, respectively, were prepared by electrolytic deposition and using phosphorous acid as phosphorous resource. The high-temperature oxidation resistance of the alloy coating was investigated using weight-gain method and X-ray diffraction (XRD). The results indicate that the addition of P could improve the high-temperature oxidation resistance of the alloy coating. The alloy coating with P atom fraction of 3.9% had the best high-temperature oxidation resistance. But the high-temperature oxidation resistance of the alloy coating decreased with the further increase of P content. When the holding temperature was below 500℃, and atom fraction of P was 3.9%, the color passivation film on the surface of alloy coating could restrain oxidation reaction remarkably. In addition, the alloy coating was amorphous at room temperature, but it transformed into crystal structure completely with constituent phases of NiO, WO₂ and Ni₃P when holding temperature was above 600℃.