The Importance of Substrate Surface Condition in Controlling the Porosity of Electroless Nickel Deposits

Summary

An overview is presented of factors affecting the porosity of EN deposits and considers three aspects: (a) the type of ferrous material (e.g. ‘Pyrene’ steel panels, machined steel, cast iron), (b) the nature and degree of surface roughness (produced e.g. by abrasive papers, grit blasting or chemical cleaning) and (c) the type of chemical pretreatment applied to the steel. A range of different substrate types (grit blasted, ground, milled and cold rolled) have been electroless nickel plated to three different thicknesses and tested for porosity. The nature of the type of pretreatment and its effect on deposit porosity has also been investigated. Talysurf measurements have shown that the surface morphology does not change significantly with deposit thicknesses up to 24 μm.

Data obtained from microscopy, profilometric, electrochemical and corrosion rate measurements are used to illustrate the importance of these factors in controlling the degree of porosity in the EN deposit and the rate of corrosion of the steel substrate. It has been shown that choice of an adequate cleaning cycle is critically important to obtain pore free deposits.