Microstructure and mechanical properties of CrFeNiBx eutectic high entropy alloys

A series of low-cost CrFeNiBx (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3) High Entropy Alloys (HEAs) without the Co element were proposed by vacuum arc melting. The study aimed to investigate the effect of boron (B) content on the microstructure evolution, phase formation regulation, and compression properties. The alloys were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The results show that with the addition of B content, the microstructure of the CrFeNiBx alloys transforms from a single-phase face-centered cubic structure to a biphasic structure consisting of Face-Centered Cubic (FCC) + irregular lamellar boride. Furthermore, the mechanical properties of alloys exhibit an increase in strength and hardness, accompanied by a decrease in compressibility. Specifically, the CrFeNiB0.25 alloy exhibited a fully eutectic structure consisting of irregular lamellar FCC + boride phases. It possesses exceptional mechanical properties, such as a yield strength of 973 MPa, compression over 80% without fracturing, and a hardness of 370 HV. The predicted phase judgment range of the high-entropy alloy containing B is as follows: when δ ≥ 3.48% and ΔHmix ≤ −6.03 kJ/mol, the boride phase appears in the solid solution phase, and when rm/rQ < 0.711, the microstructures are composed of FCC + boride phases. When rm/rQ ≥0.711, the microstructures are composed of FCC + Body-Center Cubic (BCC) + boride phases.