Fine-tuning Ni-W-Se coatings via SeO2 and lactic acid composition control

Abstract

Ni-W-Se coatings were prepared through electrodeposition using varying concentrations of SeO₂ and lactic acid in the electrolyte. The relationship between process parameters and coating properties was evaluated using analysis of variance (ANOVA). The results indicate that increasing either the SeO₂ or lactic acid concentration in the plating bath effectively enhances the coating thickness. The resulting coatings primarily consist of pure-phase Ni and Se, along with the binary compounds NiSe and WSe₂. At low lactic acid concentrations (0.15 and 0.25 M), the coating primarily consists of Ni, Se, and WSe₂. However, when the lactic acid concentration is increased to 0.35 M, under low SeO₂ concentrations (0.4 and 0.5 g L⁻¹), the deposition produces not only the existing Se and WSe₂ phases but forms the NiSe intermetallic compound. When the SeO₂ concentration is further increased to 0.6 g L⁻¹, the formation of the NiSe phase is suppressed, which reverts to a mixed phase consisting of Ni, Se, and WSe₂. The hardness of the Ni-W-Se coatings increases with the W content, reaching its highest value (484.1 HV) at SeO₂ and lactic acid concentrations of 0.6 g L⁻¹ and 0.25 M, respectively. The coating with low SeO₂ concentration and 0.15 M lactic acid (NWS-A-0.4 and NWS-A-0.5) exhibited the lowest surface roughness. The corrosion resistance of the coatings is inversely related to their Se content and surface roughness, with the NWS-A-0.4 sample showing the best corrosion resistance (I_corr: 14.13 μA cm⁻²) among all the samples.