Synthesis of ultrafine dual-phase structure in CrFeCoNiAl_0.6 high entropy alloy via solid-state phase transformation during sub-rapid solidification

High entropy alloys (HEAs) with superb mechanical properties have been traditionally produced by solidification and subsequent heat treatment. In this paper, we demonstrate a new route via one-step process using sub-rapid cooling. Under proper cooling rates, the CrFeCoNiAl_0.6 HEA could form ultrafine FCC+BCC dual-phase structure. By varying cooling rate, we can control the fraction of the BCC phase and refinement of FCC microstructures that have tunable mechanical properties in yield strength and hardness ranging from ∼580 to ∼1460 MPa and ∼260 to ∼550 Hv. We show that the structure-property-processing relation originates from the sideplate microstructures formed during fast cooling that have specific crystallographic orientation relationship between the FCC and BCC phases and chemical segregation. This work provides a new setting for better understanding of the solid-state phase transformation in HEAs under sub-rapid solidification conditions as well as a novel method for development of high-performance HEAs.