Role of CeO2coating in enhancing high temperature corrosion resistance of Ni-base superalloys as an inhibitor

Abstract

Superalloys have been used successfully to resist high temperature corrosion; however, they still lack resistance to corrosion during longer periods of use. Inhibitors and fuel additives have been used to reduce corrosion rates with varying degrees of success. In the present investigation, high temperature corrosion studies were conducted on two Ni-base superalloys, namely Superni 718 and Superni 601, in a simulated boiler environment (Na2SO4–60%V2O5), with and without the presence of a CeO2 coating as an inhibitor. Accelerated corrosion testing was carried out in a silicon carbide tube furnace under cyclic conditions at 900°C for 50 cycles. Weight change measurements were made after each cycle. The corroded samples were characterised by SEM, XRD and EPMA techniques. Superni 601 was found to be more corrosion resistant than Superni 718 in the Na2SO4–60%V2O5 environment. The presence of CeO2 in the environment reduced the rate of corrosion of both the alloys, which was attributed to the presence of unreacted CeO2 on the surfaces of the samples. The presence of a Cr2O3 layer in the oxide scale and a dense, thin Cr2O3 layer at the substrate – scale interface may also be a contributing factor for the protection of these alloys.