Microstructural stability of Fe–Cr–Al alloys at 450–550 °C

• Long-term microstructural stability of Fe–Cr–Al alloys at 450–550 °C was studied.
• No α–α′ phase separation was observed in any of the Fe–10Cr–Al alloys.
• The two-band model for Fe–Cr was extended with Al interactions.
• KMC simulations of the same alloys yielded results in agreement with experiments.
• Limit compositions were calculated to 13Cr–4Al at 475 °C and to 11Cr–4Al at 328 °C.

Iron–Chromium–Aluminium (Fe–Cr–Al) alloys have been widely investigated as candidate materials for various nuclear applications. Albeit the excellent corrosion resistance, conventional Fe–Cr–Al alloys suffer from α–α′ phase separation and embrittlement when subjected to temperatures up to 500 °C, due to their high Cr-content. Low-Cr Fe–Cr–Al alloys are anticipated to be embrittlement resistant and provide adequate oxidation properties, yet long-term aging experiments and simulations are lacking in literature. In this study, Fe–10Cr–(4–8)Al alloys and a Fe–21Cr–5Al were thermally aged in the temperature interval of 450–550 °C for times up to 10,000 h, and the microstructures were evaluated mainly using atom probe tomography. In addition, a Kinetic Monte Carlo (KMC) model of the Fe–Cr–Al system was developed. No phase separation was observed in the Fe–10Cr–(4–8)Al alloys, and the developed KMC model yielded results in good agreement with the experimental data.