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.