A Research of Intergranular Corrosion Sensitivity and Passive Film of Alloy 690

Abstract

The susceptibility to intergranular corrosion (IGC) in 2M H2SO4+0.001M KSCN of alloy 690 under different thermal treatment (TT) has been investigated using double-loop electrochemical potentiokinetic reactivating (DL-EPR). The chemical composition and the semiconducting properties of passive films formed on alloy 690 in nitric acid were studied by using X-ray photoelectron spectrom (XPS) and the Mott-Schottky (M-S) analysis. The optimum heat treatment of resistant to IGC is solution treatment in 1090°C for 2min followed by the thermal treatment in 715°C for 10h. The M-S curves indicate the specimen has produced the n-type and the p-type semiconductor at 0.08V and 0.6V, respectively. And when the thermal-treatment temperature is higher than 715°C, they become denser. The reason is the passive films which produced in the HNO3 solution is mainly chromium oxide, and as the raise of thermal treatment temperature, the content of iron oxide reduces rapidly, and leads to a compact passive film

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