Effects of annealing temperature on the crystal structure and properties of electroless deposited Ni-W-Cr-P alloy coatings

Ni-W-Cr-P alloy coatings were prepared by electroless deposition. The effects of the annealing temperature on the crystal structure, microhardness, and corrosion resistance of these Ni-W-Cr-P alloy coatings were studied. The experimental results show that the crystal structure of these alloy coatings changes with the increase of annealing temperature. That is, as-deposited Ni-W-Cr-P alloy coatings possess amorphous structure, gradually begin to crystallize at 300 °C; Ni3P phase is completely formed at 500 °C, and Ni17-W3 and Cr-Fe phases were formed at 600 °C; Ni3P is completely decomposed into Ni, W, Cr, Fe alloy films at 700 °C; the alloy coatings mainly consisted of Ni17W3 and Ni-Cr-Fe phases at 800 °C. Annealing temperature dependence of the microhardness and corrosion resistance of the alloy coatings was also measured. These results show that the Ni-W-Cr-P alloy coatings annealed at 800 °C exhibit better microhardness and corrosion resistance than those of the alloy coatings with other annealing temperature. The related strengthening mechanisms in the electroless deposited Ni-W-Cr-P alloy coatings were also discussed.