Long-Term Thermal Stability and Oxidation Resistance of HAYNES 233 Alloy

HAYNES 233 alloy is an alumina-forming alloy developed for use in a variety of high temperature applications. It is unique in the marketplace for having a combination of high creep strength and excellent oxidation and high temperature corrosion resistance to temperatures of 2000°F (1093 °C) and above while still being readily fabricable (formable, weldable, etc.). The alloy may be used in the solution annealed conditions at these high temperatures, or age-hardened to provide high strength at intermediate temperatures while maintaining its oxidation/corrosion resistance. This study will explore the long-term performance of 233 alloy in terms of microstructural stability, tensile properties, and oxidation resistance. Thermal exposures of up to 8000 h were explored at temperatures ranging from 1200°F (649 °C) to 1800°F (982 °C). The effect of the initial material condition (solution annealed vs. age-hardened) was considered as well. It was found that prior age-hardening can provide the alloy with significantly improved ductility at intermediate temperatures before and after thermal exposure. A comparative year-long oxidation test at 2000°F (1093 °C) confirmed the excellent oxidation resistance of the alumina-forming 233 alloy compared to competing alloys (typically chromia formers).