Effect of Microstructure of Ferrous Substrate on Porosity of Electroless Nickel Coating

The corrosion resistance of electroless nickel (EN) coatings on ferrous substrates is affected by coating porosity. Carbon and iron carbide are present in the microstructure of ferrous alloys. If the sites of carbon and iron carbide are not catalytically active to EN deposition as the rest of substrate surface, there is a possibility of pore formation on these sites. In the present study, the rate of EN deposition on carbon, iron carbide and steel surfaces was individually measured. The locations of EN deposit on the microstructure of a ferrous alloy was mapped with the SEM/EDS technique and was compared to the locations of carbon on the original substrate surface. This paper summarizes the results of these investigations.