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.
