Role of CeO_2 coating in enhancing high temperature corrosion resistance of Ni-base superalloys as an inhibitor

摘要

Superalloys have been used successfully to resist high temperature corrosion; however, they still lackresistance to corrosion during longer periods of use. Inhibitors and fuel additives have been used toreduce corrosion rates with varying degrees of success. In the present investigation, high temperaturecorrosion studies were conducted on two Ni-base superalloys, namely Superni 718 and Superni 601,in a simulated boiler environment (Na_2SO_4-60%V_2O_5), with and without the presence of a CeO_2 coating as an inhibitor. Accelerated corrosion testing was carried out in a silicon carbide tube furnaceunder cyclic conditions at 900°C for 50 cycles. Weight change measurements were made after eachcycle. The corroded samples were characterised by SEM, XRD and EPMA techniques. Superni 601was found to be more corrosion resistant than Superni 718 in the Na_2SO_4-60%V_2O_5 environment.The presence of CeO_2 in the environment reduced the rate of corrosion of both the alloys, which wasattributed to the presence of unreacted CeO_2 on the surfaces of the samples. The presence of a Cr_2O_3 layer in the oxide scale and a dense, thin Cr_2O_3 layer at the substrate–scale interface may also be acontributing factor for the protection of these alloys.