材料期刊网

The corrosion of a Ni-20Cr and three ternary Ni-20Cr-Cu alloys containing 10, 20 and 30 wt.% Cu, respectively, in a eutectic (Li, K)(2)CO3 melt was studied at 650 degrees C under air. Ni-20Cr and Ni-20Cr-10Cu are solid-solution alloys, while both Ni-20Cr-20Cu and Ni-20Cr-30Cu are two-phase alloys composed of a Cu-depleted matrix together with a small amount of a Cu-rich phase. The results indicate that Ni-20Cr and Ni-20Cr-10Cu have similar corrosion rates, forming a scale of external NiO and inner Cr-rich oxides. The two-phase Ni-20Cr-20/30 Cu alloys corrode rapidly, producing a mixture of Ni-Cr-rich oxides and a Ni-Cu metallic phase, which may be ascribed to the accelerated corrosion of the Cu-depleted matrix coupled with the cathodic Cu-rich phase of the alloys. As compared to Ni-20Cr-30Cu, Ni-20Cr-20Cu suffers from more-severe corrosion, due to a smaller area fraction of the cathodic Cu-rich phase in the alloy. The galvanic corrosion mechanism is also discussed.