Abstract: The coarse-grain size of eutectic high-entropy alloys (EHEAs) after casting always results in significantly worse fatigue properties, which greatly limit their applications in marine engineering. In the present work, three different multiscale heterogeneous nanostructured (HN) AlCoCrFe_xNi_y alloys (x = 1 and y = 2; x = 1.5 and y = 1.5; and x = 2 and y = 1) with phase transformation-induced plasticity (TRIP) effect were fabricated to improve the fatigue properties of conventional EHEAs. The experimental results revealed that the microstructures of all three alloys were composed of FCC and B2 phases, and the grain size in both phases ranged between 50 nm and 2 µm. The tensile strength, low-cycle fatigue lifetime of the three HN EHEAs were, respectively, 30 % greater, 2.5-10 times longer than those of the conventionally cast EHEAs. Among the three HN alloys, the AlCoCrFe_1.5Ni_1.5 alloy manifested the best overall mechanical properties. In-situ electron backscatter diffraction results and high-resolution transmission electron microscopy observations indicated that the HN microstructure and the TRIP effect simultaneously improved the strength and ductility of the as-prepared EHEAs and also effectively suppressed crack formation and propagation under cyclic loading. These results demonstrate that ultrahigh-strength EHEAs with excellent fatigue properties can be developed using this method, shedding light on the design of future novel structural materials.

Key words: High-entropy alloy, Nanostructure, Heterogeneous structure, Fatigue, Ultra-high strength