Thermal cycle length can severely affect long-term oxidation behavior of high-temperature alloys. The present study is focused on the effect of thermal cycle length (twelve 30-day cycles versus six 60-day cycles) on the long-term (360 days) oxidation behavior of various chromia-forming alloys at 982°C, 1092°C, and 1149°C (1800°F, 2000°F, and 2100°F). The alloys included in this study are HAYNES® 230® alloy, 617 alloy, HR-160® alloy, HR-120® alloy, and 800HT® alloy. Alloy performances were assessed by analyzing the weight-change behavior and extent of attack as measured by metal loss and average internal penetration. The 230 and 617 alloys exhibited excellent oxidation resistance under both cycling conditions, presumably due to their ability to form and maintain adherent oxide scale. In particular, alloys with high Fe contents underwent accelerated oxidation attack. There was a significant increase in the extent of attack with increase in number of cycles (i.e. shorter cycle length). Moreover, the effect of cycle length was most pronounced at the highest test temperature (1149°C), and a strong correlation was found between oxidation kinetics and alloy composition as well as oxidation kinetics and the cycle length. HAYNES, 230, HR-160, HR-120 are registered trademarks of Haynes International, Inc. 800HT is a registered trademark of Special Metals Corporation.

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