Excellent Properties of Ni-15 wt.% W Alloy Electrodeposited from a Low-Temperature Pyrophosphate System

Electrodeposited Ni-W alloy coatings are considered to be one of the most suitable candidate coatings to replace carcinogenic hexavalent chromium coatings. In this work, Ni-W alloys are electrodeposited from pyrophosphate baths containing different concentrations of Na2WO4 2H(2)O (C-W) at 40 & DEG;C. Both C-W and the applied current density can affect the W content in the coatings. The effect of C-W becomes weaker with the increased current density. The Ni-W alloys with 15 & PLUSMN; 5 wt.% W (Ni-15 wt.% W) are obtained from the bath containing 40 g L-1 C-W at a high current of 8 A dm(-2). The microhardness, corrosion resistance and hydrogen evolution reaction (HER) are measured with a microhardness tester and an electrochemical workstation. The modified properties are studied by heat treatment from 200 to 700 & DEG;C. The highest microhardness of 895.62 HV and the better HER property is presented after heat treatment at 400 & DEG;C, while the best corrosion resistance in 3.5 wt.% NaCl solution appears at 600 & DEG;C.

Automated summary

Electrodeposited Ni-W alloy coatings are considered a suitable alternative to carcinogenic hexavalent chromium coatings. The W content in the coatings is influenced by both the concentration of Na2WO4 2H(2)O (C-W) and the applied current density, with the effect of C-W becoming weaker at higher current densities. The highest microhardness and best hydrogen evolution reaction (HER) property are achieved after heat treatment at 400°C, while the best corrosion resistance in a 3.5 wt.% NaCl solution is seen at 600°C.