Electrodeposition of Ni-W-P alloy

Abstract

Influence of sodium hypophosphite admixture to electrolyte for deposition of Ni-W alloy on the coating composition, morphology, structure and microhardness is investigated. Antisymbatic dependence of tungsten and phosphorus content in Ni-W and Ni-W-P alloys on the sodium hypophosphite concentration in the electrolyte is observed, namely, at higher sodium hypophosphite concentration in the electrolyte solution the coatings are become poorer in tungsten whereas phosphorus content is increased. Phosphorus incorporation into the alloy leads to globular morphology of the surface of coatings. The minimal roughness was obtained at high hypophosphite concentrations in the electrolyte (7.5 and 10 g/L). As-deposited Ni-W and Ni-W-P alloys possess nanocrystalline structure manifested in broad X-ray diffraction peaks. Addition of 2.5…5 g/L of hypophosphite markedly weakens Ni reflections (200) and (220), the (111) peaks becomes broader. In addition, a Ni3P phase is appeared in the coatings. Thermal treatment in vacuum at 400 °С induces growth of nickel crystallites. Microhardness of as-deposited coatings is weakly dependent on sodium hypophosphite concentration in the electrolyte and is in the range 3.8…4.2 GPa. Thermal treatment of Ni-W-P alloys at 400 °С during 1 h increases microhardness up to 5.9…8.8 GPa.