Galvanic Corrosion in Molten Salts: A Discussion of the Corrosion Mechanism of Two-Phase Ni–20Cr–20/30Cu Alloys in Eutectic (Li,K)₂CO₃ at 650°C

Abstract

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)₂CO₃ melt was studied at 650°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.