Aluminum suppression of α′ precipitate in model Fe–Cr–Al alloys during long-term aging at 475 °C

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2020-01, Vol.772, p.138714, Article 138714
• Main Authors: Yang, Z., Wang, Z.X., Xia, C.H., Ouyang, M.H., Peng, J.C., Zhang, H.W., Xiao, X.S.
• Format: Article
• Language: English
• Subjects: Aging; Aging (metallurgy); Alloys; Aluminum; Chromium; Coarsening; Composition; Equilibrium; Ferrous alloys; Fe–Cr–Al alloys; Iron; Long-term aging; Nucleation; Phase diagrams; Phase separation; Precipitate; Variations
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2019.138714

Aluminum suppression of the α′ precipitate has been observed in eight model Fe–Cr–Al alloys with nominal compositions ranging from 11 to 20 wt% Cr and 4.5 to 6 wt% Al during long-term aging at 475 °C for up to 10,000 h. Fe–15Cr-4.5Al alloy reached the equilibrium state after aging for 10,000 h, in which the α′ phase evolution involved an integrated process of nucleation, growth, and coarsening. Meanwhile, no α-α′ phase separation occurred in the Fe–15Cr–6Al alloy during long-term aging at 475 °C. The α′ phase precipitated in the Fe–17Cr–6Al and Fe–20Cr–6Al alloys during the intermediate stage of aging, due to the inevitable composition fluctuation, and was eventually dissolved in the matrix in the later stages of aging. As such, a further increase in Al concentration (6 wt%) can strongly suppress the α′ precipitate in the equilibrium state. The equilibrium phase diagram of the Fe–Cr–Al system at 475 °C, which is based on the present work and previous literature, is expected to provide a more accurate reference for optimizing Fe–Cr–Al alloys for fuel cladding.