Structural, Mechanical, and Corrosion Resistance Properties in 3.5% NaCl Solution of Electroless Deposited Ternary Ni–P–W System

Low phosphorous electroless Ni–P coating containing W was prepared by incorporating sodium tungstate at different concentrations in a commercial low phosphorous electroless nickel bath. A total of five samples of Ni–P–W were prepared with different concentrations and compared with commercial low-P EN coating. The structure and the microstructure analysis showed Ni phase in as-plated samples and Ni and Ni3P phase in the heat-treated samples. The results from SEM-EDS show no presence of W which was also confirmed by using ICP-OES analysis. The microhardness evaluated on the cross-section of the samples followed the standard trend of a low phosphorous coating. Potentiodynamic polarization test in 3.5% NaCl showed that the corrosion rate decreases by an order of magnitude after heat treatment at 400 °C for 1 h. Similar observation was made from the EIS studies of the as-plated and heat-treated samples. Heat treatment decreases the corrosion rate by an order of magnitude when compared to the as-plated samples.