Corrosion behaviors of Ni base solid solution-toughened Cr₁₃Ni₅Si₂ alloy in Cl?containing solutions

From the application point of view, corrosion resistance of materials in corrosive environments, especially in Cl^- containing medium, has great significance when used as mechanical components serving in marine and other aggressive environments. The corrosion behavior of a material is largely controlled by the presence or absence of protective surface film, which may act as a protective barrier against corrosion attacks. Therefore, the corrosion resistance of an alloy is closely related to the particular composition of the passive film and the synergistic interaction between the cations of alloy components in the passive film. In the present study, a γ-toughened Cr₁₃Ni₅Si₂ metal silicide alloy, consisting of Cr₁₃Ni₅Si₂, Ni base solid solution γ and Cr₃Ni₅Si₂ was designed and fabricated by the introduction melting and die-casting prosess. Corrosion behaviors of the alloy in a series of Na₂SO₄+NaCl solutions were investigated by anodic polarization, Tafel plot and electrochemical impedance spectroscopy (EIS) experiments. Chemical composition of the passive film and the surface of polarized samples were examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. A commercial solution treated single phase austenitic stainless steel 1Cr18Ni9Ti was selected as the reference material for all the electrochemical tests. Results showed that the metal silicide alloy exhibited high corrosion resistance in all testing solutions due to the formation of a compact and protective passive film composed mainly of Cr₂O₃, as well as the high chemical stability of Cr₁₃Ni₅Si₂ and Cr₃Ni₅Si₂ phases. No evidence of localized corrosion occurred even after anodic polarization in 0.1 mol/L Na₂SO₄+1 mol/L NaCl solution. Moreover, the corrosion potential, breakdown potential and anodic current density are almost invariant with increasing Cl^- concentration, which means the alloy has excellent corrosion resistance in neutral Cl^- containing solutions.