The effect of microstructure for Ni-based surface finishing thin film on corrosion behavior

Electroless and electroplated single-layer Ni and multilayer Ni/Pd/Au were used as surface finishing materials for automobile device substrates. When the samples were placed in a chamber with various gaseous SO₂ concentrations, better corrosion resistance was observed for single-layer electroless Ni and multilayer electroplated Ni/Pd/Au compared with their well-crystalline electroplated and electroless counterparts, respectively. Electrochemical analysis and materials characterization are adopted to investigate the disparate corrosion behaviors. Galvanically displaced Pd(P) and immersion Au with a high grain boundary density provided a large number of diffusion paths for the increased growth of corrosion products on the electroless Ni/Pd/Au surface than on the electroplated surface. Reduced hydrogen gas formed blisters exerting pressure on the grain boundaries and causing defects that may enhance the diffusion of the atoms. These results proved that the microstructure and crystallinity of surface finishing films have a predominant effect on their corrosion behaviors.