Role of CaO inhibitor in enhancing high‐temperature corrosion resistance of some Ni‐based superalloys

Abstract

High-temperature corrosion of metals and alloys can be controlled by the use of inhibitors and fuel additives. In this work, the role of a superficially applied CaO coating to combat high-temperature corrosion of some Ni base superalloys viz Superni 75 (alloy A), Superni 718 (alloy B), and Superni 601 (alloy C) has been investigated. Accelerated corrosion testing of the coated as well as bare superalloys was done in a molten salt environment (Na2SO4-60% V2O5) at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a silicon carbide tube furnace followed by 20 min cooling in ambient air. Weight change measurements after each cycle were taken by an electronic balance having an accuracy of 0.01 mg. X-ray diffraction (XRD), scanning electron microscope (SEM), and electron probe micro analysis (EPMA) analyses of the exposed specimens were carried out to characterize the oxide scales. The bare superalloys showed more overall weight gains, in general, in comparison with their CaO-coated counterparts. It was concluded that CaO was most effective in reducing corrosion rate in alloy A.