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Early-stage oxidation behavior of Co-rich high-temperature alloys



The long-term oxidation performance of an alloy is critically linked to the early-stage oxidation behavior of high-temperature alloys. This study investigates early-stage oxidation behavior in terms of oxidation kinetics, scale evolution, and residual stresses developed within a scale of the commercially available cobalt-rich alloys: HAYNES® 188, 6B, 25, and HR-160® and a newly developed nitride-dispersion strengthened NS-163® alloy (HAYNES®, HR-160®, NS-163® are registered trademarks of Haynes International, Inc). Short-term isothermal oxidation exposures were conducted in flowing air at 982 °C for durations of 1–50 h. Oxidation kinetics was assessed by weight-change behavior, which showed that 188 alloy exhibited the lowest weight-gain, while for similar times HR-160 alloy underwent weight-loss. SEM/EDS analysis was performed to characterize oxides formed in these alloys, while stresses developed in the oxides of different alloys were measured using synchrotron X-ray radiation. The results in this paper clearly demonstrated the effects of alloy composition on the scale evolution and the amount of stresses developed in oxides.