Ammonia-induced corrosion of Fe- and Ni-based alloys at 400 °C-1000 °C: Degradation mechanisms and materials suitability for ammonia-handling components

Ammonia is a promising carbon-free fuel for future energy systems. However, ammonia-induced corrosion remains a critical challenge for structural alloys. This study evaluates the corrosion susceptibility and degradation mechanisms of Fe-based alloys (SUS304, SUS316, and SUS310) and Ni-based alloys (Inconel 600 and Hastelloy X) exposed to a flowing 20 vol% NH 3 /N 2 mixture at 400–1000 °C for 20 and 100 h. Phase analysis, microstructural characterization, and thermodynamic calculations were used to elucidate alloy degradation. Weight gain correlated well with the total concentration of nitride-forming elements. Cr-based nitrides, primarily CrN, formed in all alloys. SUS310 and the high-Ni alloys exhibited severe cracking and spallation at 500–600 °C and 400–500 °C, respectively, even after short exposures. In contrast, coarse CrN formed without detectable cracking at 700–1000 °C. Alloy degradation mechanisms are proposed for distinct temperature regimes, and the suitability of these materials for components in flowing-ammonia environments is assessed.