CS-AFM study on Pb-induced degradation of passive film on nickel-based alloy in high temperature and high pressure water

The degradation mechanism of trace Pb on nickel-based alloy passive film in pure water at 270 °C is researched by surface analysis techniques and calculations. Experimental results show that Pb reduces the oxygen content and alters the composition of the passive film, resulting in the remarkable drop in its localized electrical resistivity. Density functional theory (DFT) and thermodynamic calculation reveal that the presence of Pb has two effect on the formation of passive film. One is to retard the outward diffusion of oxygen vacancies in the oxide layer, and the other is to affect the dehydration of Cr(OH)3 and Ni(OH)2.