Abstract
Ni-W-Cr-P alloy coatings were prepared by electroless deposition on Al₉Si compound. The effect of heat treatment on the structure and property of prepared coatings was validly investigated. XRD analysis showed that the as-deposited coatings were Ni-W-Cr-P solid solution. Interestingly, the Ni₃P phase was observed in the samples annealed at 400 °C, meanwhile, the heat treatment at 500 °C process resulted in the formation of Ni₃P, Cr_1.12Ni_2.88 and Al_0.983Cr_0.017 phases. Two brand new (AlSi) ₇Ni₃ and Al₃Ni₂ phases were identified in the coatings annealed at 600 °C. The experimental results reveal that the as-deposited Ni-W-Cr-P alloy coatings exhibit higher microhardness and better corrosion resistance comparing with those of as-deposited Ni-P and Ni-W-P coatings. At higher annealing temperature, the microhardness of the Ni-W-Cr-P alloy coatings increased, got to the maximum value at 500 °C, and decreased slightly for the samples annealed at higher temperature. It is worth noting that the corrosion resistance was also remarkably improved by heat treatment.

Key words
electroless deposition, Ni-W-Cr-P alloy coatings, heat treatment, phase transformation behavior, microhardness, corrosion resistance

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