Fe-Mn-Al-C high-entropy steels with superior mechanical properties at 4.2 K

There exist urgent demands to develop structural materials with superior mechanical properties at 4.2 K. Some high-entropy steels (HESs) show potentials as cryogenic materials, but their deformation behaviors and mechanical properties at 4.2 K have been rarely investigated. Moreover, the aging-induced embrit-tlement of HESs also severely restricts their applications. In this work, the Fe-Mn-Al-C HESs with different Al contents (0, 4, 10 or 15 at.%) and grain sizes were fabricated, and their deformation behaviors and mechanical properties at 4.2 K were systematically studied. With increasing the Al content, (Fe, Mn)23C6 carbides are effectively inhibited in 10%Al HES after aging at 923 K for 10 days. Therefore, the premature fracture of 10%Al HES is avoided, leading to the excellent combination of high strength (-1.5 GPa) and high fracture toughness (255 MPaGreek ano teleiam1/2) at 4.2 K. The deformation mechanisms shift from the extensive twinning and deformation bands in 0Al HES to the lesser twinning, Taylor lattices and deformation bands in 10%Al HES, which contribute to the high strength and ductility of the 10%Al HES. Furthermore, the 10%Al HES with larger grains displays a much higher fracture toughness at 4.2 K, and this inverse size effect on the cryogenic toughness was elaborately revealed. (c) 2023 Northeastern University. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).