Phase equilibria among η-Fe2Al5 and its higher-ordered phases

• Published in: Science and technology of advanced materials 2021, Vol.22 (1), p.373-385
• Main Authors: Hamada, Tetsuya, Higashi, Masaya, Niitsu, Kodai, Inui, Haruyuki
• Format: Article
• Language: English
• Subjects: 10 Engineering and Structural materials; 106 Metallic materials; 212 Surface and interfaces; 501 Chemical analyses; 503 TEM, STEM, SEM; aluminized steel; antiphase boundary; Fe-Al; galvanized steel; intermetallic compound; phase diagram; Phase equilibrium; plating; superlattice structure
• ISSN: 1468-6996; 1878-5514
• DOI: 10.1080/14686996.2021.1915691

Phase equilibria among the η-Fe 2 Al 5 phase and its higher-ordered phases with the η framework structure were determined experimentally. The solubility range of the η phase at elevated temperature does not differ remarkably from that in previous studies, but this phase is found to undergo complicated phase transformations upon cooling. Four phases are present, namely η', η", η"' and η m , with higher-order atomic orderings in the c-axis chain sites of the orthorhombic crystal structure of the parent η phase. The η" and η"' phases form on the Al-poor and Al-rich sides, respectively, in equilibrium with the ζ-FeAl 2 phase below ~415°C and θ-Fe 4 Al 13 phase below ~405°C. The η' and η m phases become stable below 312°C and 343°C with the peritectoid reactions η' → η m  + η"' and η m → η + η", respectively. The η phase is not stable below 331°C with the eutectoid reaction of η m  + η"' → η. On the basis of these findings, we unraveled the phase equilibria among the η-Fe 2 Al 5 phase and its higher-ordered phases with the η framework structure.