Hot-corrosion behavior associated with the evolution of corrosion scales of a Ni-based superalloy in molten salts

Abstract The degradation of Ni-based superalloys in molten salts is closely related with the evolution of corrosion scales. In this work, the evolution of corrosion scales, the characteristics of the scale/alloy matrix interface associated with the corrosion mechanisms and the corrosion kinetics of a Ni-based superalloy Ni–20Cr–18W in molten salts were investigated. The outer surface of the corrosion scales was composed of numerous flakes. From the cross-sectional view, the scales gradually presented a layered structure and its formation can be ascribed to the morphology evolution of the inclusions inserted within the scales. It was found that the corrosion progress was a cooperative process involving in both oxidation and sulfuration, and the element of sulfur (S) took the precedence to penetrate into the matrix and resulted in an obvious sulfuration zone nearby the scales/alloy matrix interface. The corrosion activation energy of the investigated alloy was calculated to be 125.27 ​kJ/mol. This work is expected to work out the structural evolution of the corrosion scales and the characteristics of the scale/matrix interface associated with the corrosion mechanisms for Ni-based superalloys.