The effect of carbon and silicon variation on the oxidation resistance of a cobalt-based superalloy
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Elsevier
Department of Materials Science and Metallurgy
https://doi.org/10.1016/j.corsci.2026.113746
Department of Materials Science and Metallurgy
https://doi.org/10.1016/j.corsci.2026.113746
Abstract
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Understanding the oxidation behaviour of Co-based superalloys is crucial for the deployment of such alloys for high-temperature structural applications. This study explores the oxidation behaviour of four cast Co-based superalloys with varying C (0.25 or 0.5 wt%) and Si (1 or 4 wt%) contents at 800°C, 1000°C, and 1200°C for up to 100 h. Alloys with higher Si content generally exhibited lower isothermal mass gains than the lower Si variants, although the benefit depended on temperature and was accompanied by differences in the scale loss during cooling. At 800°C, an oxidation-associated Laves phase formed within surface-breaking interdendritic oxidation channels in the high-Si alloys (associated with M12C), consistent with reduced short-circuit transport along these pathways and the lower measured rates of isothermal mass gain. At 1000°C, Laves formation persisted but occurred as coarser particles and did not produce a measurable separation in mass gain. Notably, the high-Si alloys exhibited increased oxide spallation during cooling from this temperature. At 1200°C, the high-Si alloys developed a more continuous silica subscale at the alloy-oxide interface, along with a modest reduction in isothermal mass gain relative to the low-Si alloys. For alloys with equivalent Si content, reduced C improved mass-gain behaviour at 800°C and 1200°C, consistent with a reduced extent of interdendritic network (greater interdendritic spacing), whereas at 1000°C all alloys exhibited broadly similar mass gains. These findings demonstrate that Si and C influence oxidation through coupled effects on scale constitution, microstructurally controlled transport and oxide-scale integrity, providing guidance for the design of next-generation high-temperature alloys.
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