Phase dependent early-stage dissolution behavior of 2205 duplex stainless steel in the passive state

Duplex stainless steel 2205 comprises α (bcc) and γ (fcc) phases with distinct element distributions, making the two phases exhibit different passivation and corrosion resistance. However, the phase-dependent dissolution behaviors in the passive state are still unclear. This work compares the electrochemical corrosion and passive film characteristics of single-phase α and γ samples in 3.5%NaCl solution in the passive state, and reveals the mechanism of their different dissolution behaviors. It is found that α phase contains higher contents of Cr and Mo, whereas γ phase bears doubled Ni content. Under galvanostatic polarization condition in the passive state, γ phase undergoes severer dissolution than α phase. Both phases form bilayer passive films, and the film on α phase is ∼0.5 nm thicker, featuring 3-5 times lower point defect density, higher peak Cr content (26.8%), and higher fraction of Cr2O3 in the inner layer. The superior corrosion resistance of α phase originates from the synergistic advantages of thicker, denser, and Cr-enriched passive film. Our findings can guide the compositional and microstructural design of duplex stainless steels to improve their service performances in marine environments.