Tuning the mechanical behavior of high-entropy alloys via controlling cooling rates

The microstructures determine the macro-mechanical properties in metals and alloys. However, the formation mechanism of microstructures in high-entropy alloys (HEAs) rapidly cooled to room temperature still remains unknown at nanoscale. Here, we present the AlCoCrCuFeNi HEAs prepared by various cooling rates and the deformation behaviour using molecular dynamic simulation. The results show that the radial distribution function of HEAs is in good agreement with the previous experimental result. The amorphous HEA is formed at high cooling rates, while the nanocrystalline HEA is generated at low cooling rates. The hybrid amorphous-crystallization structured HEA occurs at middle cooling rates. For low cooling rates, the considerable amount of face-centered-cubic and hexagonal-close-packed short-range orders clearly show the crystal-nucleation process in the supercooled liquid of HEAs. The high residual hydrostatic stress around grain boundaries is observed in the nanocrystaline HEAs. Moreover, the nanocrystal HEA presents a high strength, compared to the amorphous HEA. The amorphous HEA exhibits the stable flow stress due to no obvious local stress concentration. This result could help guide the preparation of HEAs with a high strength by controlling the cooling rate, which generates the structural hierarchy.