Duplex Ni-P-ZrO2/Ni-P electroless coating on stainless steel

Duplex Ni–P–ZrO2/Ni–P coating was electroless deposited onto stainless steel substrates. High phosphorus Ni–P coating was plated as the inner layer to improve the corrosion resistance and low phosphorus sol-enhanced Ni–P–ZrO2 coating was on the top to strengthen the mechanical property. The microstructure, mechanical property, corrosion resistance and hydrophobic property of coating were investigated systematically. The results show that this novel duplex coating possesses both excellent mechanical property and good corrosion resistance. The microhardness was further improved from ∼648 HV100 of Ni–P/Ni–P coating to ∼752 HV100 of Ni–P–ZrO2/ Ni–P coating, while the hardness of stainless steel is below 200 HV100. The duplex coatings have very good corrosion resistance due to the different corrosion mechanism compared with the single Ni–P coating. This duplex coating also shows hydrophobic property.The project is funded by NPRP Grant #NPRP-4-662-2-249 from the Qatar National Research Fund (a member of Qatar Foundation). It is also supported by a New Zealand Marsden Grant and Auckland UniServices project. The authors would like to thank the technical stuff in the Department of Chemical and Materials Engineering and the Research Centre of Surface and Materials Science for various assistances. We also express our gratitude to Glen Slater, Chris Goode and technical stuff in Rigg Electroplating Ltd and Electroless Coating Systems Ltd.Scopu