The Study of Corrosion Resistance of Electroless Cobalt-Nickel Double Layer

摘要

Double layer of Ni-P and Co-P coatings was prepared by electroless plating with sodium hypophosphite as reducing agent. Based upon corrosion testing results of electrochemical analysis, dipping test, and salt-spray test, Ni-P coating is more inert than Co-P coating. Corrosion potentials are F_(corr)=-446mV, and E_(corr)=-585mV for Ni-P and Co-P coatings, respectively. Double layer with Co-P coating as outer layer and Ni-P coating as inner layer is more corrosion-resistant. The morphology of corrosion pattern was investigated by optical microscopy and closely related to the rearrangement order of coatings in the double layer.