Corrosion Behaviour of Ni-based Alloys 230, 617 and 601 in CO2 Gas at 750 and 850 °C

This paper investigated the corrosion behavior of three nickel-based alloys (230, 617 and 601) at 750 °C and 850 °C in a carbon dioxide environment for up to 500 h. All three alloys showed good oxidation resistance by forming mainly a protective chromia layer with low weight gains. Internal Al 2 O 3 was precipitated beneath a thin chromia layer in all cases. For 230 and 617 alloys, NiO and Cr-rich spinel outer layers were formed, but for 601 less iron and nickel outward diffusion was observed at both temperatures. Furthermore, some minor alloy elements (Mn, Ti, and Co) were also observed in the chromia layers. Very limited carburization due to the CO 2 reaction was revealed in the matrix underneath the oxide scale. Wagner’s theory was applied to examine the critical chromium concentration for forming a protective chromia scale. This prediction indicated that alloy concentrations were marginal for chromia formation at both temperatures and the critical chromium concentration decreased with increasing the oxidation temperature. The presence of other alloying elements, e.g. Al, Mn, Ti, Si etc could increase corrosion resistance of these alloys by forming either additional protective oxide barriers or integrating with chromium oxide to enhance its protection.