High-temperature oxidation resistance of alumina-forming ferritic alloys in a steam-containing atmosphere

In this study, the high-temperature steam oxidation resistance of alumina-forming ferritic alloys (AFF) alloys was investigated. A dense α-Al 2 O 3 film, heterogeneously nucleated beneath pre-formed Fe 2 O 3 /Cr 2 O 3 oxides, effectively suppressed oxygen diffusion into the substrate, resulting in significantly enhanced oxidation resistance compared to commercial austenitic stainless steels (ASS). Upon prolonged exposure at 700 °C in an air-10% H 2 O atmosphere, AFF alloys exhibited minimal weight change and no surface degradation, unlike conventional ASS alloys. These findings offer valuable insights into the design of cost-effective structural materials that require both high corrosion resistance and mechanical performance. Notably, the AFF alloys demonstrate a favorable balance between these physical properties, positioning them as strong candidates for commercialization in advanced energy systems. • In a steam-containing atmosphere at 700 °C, both the designed alumina-forming ferritic superalloys (AFFSs) and commercial austenitic stainless steels (ASSs) initially formed Fe-rich and Cr-rich oxides on the outer surface due to their faster oxidation kinetics. • In ASSs, the volatilization and subsequent depletion of Cr hinder the formation of a stable, steady-state protective Cr₂O₃ layer under high-temperature steam-containing environments, which in turn accelerates breakaway oxidation due to the absence of a continuous protective scale. • After prolonged steam exposure, a dense and stable α-Al₂O₃ layer (~100 nm thick) developed in the AFFSs, effectively suppressing both inward and outward diffusion, thereby ensuring long-term stability in a high-temperature steam-containing atmosphere. • Transient Cr₂O₃ served as a heterogeneous nucleation site for α-Al₂O₃ even at 700 °C. The high Al (16 at.%) and Cr (13.3 at.%) contents in the AFFS alloys notably promoted the development of a dense α-Al₂O₃ layer, thereby improving oxidation resistance. • The formation of the protective α-Al₂O₃ layer was largely insensitive to microstructural variations and Mo addition. While Mo had little influence on oxide formation, it contributed significantly to the mechanical properties. • The designed AFFS alloys demonstrated superior oxidation resistance and high-temperature strength synergy compared to other conventional heat-resistant alloys.