Influence of codeposition of copper on the structure and morphology of electroless Ni–W–P alloys from sulphate- and chloride-based baths

Abstract

Quaternary Ni–W–Cu–P coatings were deposited by using alkaline-citrate-based nickel sulphate and nickel chloride baths. The structure and morphology of these deposits are reported for the first time and compared with ternary Ni–W–P deposits from the same baths without copper addition. Incorporation of copper has marginal influence on the nickel, phosphorus and tungsten contents of the coatings. Increase in grain size with the incorporation of copper was found in B1-based coatings, but in the case of B2 coatings, no change is observed. In case of ternary deposits, morphology of B1-based coatings was coarse, and nodular, whereas that of B2-based coatings were smoother. Addition of copper in both B1 and B2 coatings had resulted in very smooth nodular-free deposits. XPS studies showed that addition of copper increases the elemental form of W in the chloride-based deposits towards that of sulphate-based deposits. Copper has no detrimental effect on the hardness but improves the surface quality.