Comparative Analysis on Resistance to Corrosion of the Electroless Duplex Ni-P-ZnO/Ni-P-SiC and Ni-P-Al2O3/Ni-P-SiC Coatings

Atmospheric corrosion greatly reduces the life of the various units in different fields such as industries, vehicles and residential structures. Barrier coatings are best choice to minimize or prevent the atmospheric corrosion in metals. Various barrier coating techniques include vapor deposition, thermal spraying, electroplating and electroless coatings. Out of these, the electroless Ni-P coating technique is the best choice to prevent atmospheric corrosion with economized cost. Present investigation, to improve the mild steel resistance to corrosion electroless duplex Ni-P-ZnO/Ni-P-SiC and Ni-P-Al2O3/Ni-P-SiC coatings were tried on it. In this study by using dual electroless bath multi-layer coatings is developed. Corrosion protection ability of both the coatings is measured by conducting potentiodynamic polarization tests in 3.5% NaCl solution. The above mentioned coatings subjected to heat treatment at a temperature of 400 oC to enhance the corrosion resistance of the deposit. A comparative study was carried out between both the coatings to know the better alternative to achieve good corrosion protection ability. Results confirm that Ni-P-ZnO outer layer duplex coating offers highest corrosion resistance. After thermal process, corrosion resistance of the deposit has been increased because of Phase transmission occurs to hard Ni3P from unstructured to structured hard Ni3P.