The high-temperature oxidation resistance of ERBOCo-1 and ERBOCo-1X, two multinary Co-rich alloys containing considerable Ni-additions and inverted Co/Ni ratios, was elucidated in detail by means of thermogravimetry (TGA) and detailed electron microscopy analysis. Clearly, for both alloys dendritic regions (D) were identified to be especially prone to severe internal oxidation, whereas in case of interdenritic areas (ID) much thinner and rather continuous alumina rich scales were developed [1]. As the refractory metals Ta and W were demonstrated to strongly enrich in ID and D, respectively, it was concluded that derivatives of higher Ta- (ERBOCo-1+Ta and ERBOCo-1X+Ta) and lower W-content (ERBOCo-1-W and ERBOCo-1X-W) might provide better high-temperature oxidation resistance. The current study confirms this presumption as TGA-results of all 4 derivatives at 1050 °C reveal strongly reduced oxidation kinetics compared to the original alloys. The discussion of the oxidation results focuses on the influence of refractory metals on elemental transport of protective scale forming elements, Al and Cr, making use of diffusion-couple experiments. 

[1] S.P. Hagen, M. Weiser, B. Abu-Khousa, and S. Virtanen: Metallurgical and Materials Transactions A, 2022, https://doi.org/10.1007/s11661-022-06620-6.