Porosity of Electroless Nickel Coatings Investigated Using Different Porosity Tests and Their Application

The porosity of electroless nickel coatings on mild steel substrates having different substrate surface roughness and coating thickness was investigated using NSS (Neutral Salt Spray), ferroxyl, and SO₂ tests. In addition the influence of substrate surface roughness and coating thickness upon the properties of electroless nickel coatings was studied.

It was found that all porosity tests showed the same tendency for the porosity of electroless nickel coatings to decrease with decreasing substrate surface roughness and increasing coating thickness. The use of the SO² and ferroxyl test have the advantage over the NSS test as a routine quality control procedure in that they are both quicker to carry out and easier to interpret. A relationship between porosity, substrate surface roughness and coating thickness was established which might be used as an industrial quality control tool.