Effect of cryogenic treatment on B2 nanophase, dislocation and mechanical properties of Al1.4CrFe2Ni2 (BCC) high entropy alloy

In this paper, cryogenic treatment (at 77K) was first applied to solve the problem of strength and plasticity balance of body-centered cubic (BCC) type Al1.4CrFe2Ni2 high entropy alloy (HEA). The microstructure and mechanical properties of the HEAs after cryogenic treatment was studied systematically. The results show that cryogenic treatment has an intensive effect on the nanophases (B2), dislocations and mechanical properties. The nanophase is refined to 126.05 nm with cryogenic treatment for 24 h, which is 42.7% lower than the matrix alloy. The number of the nanophase is increased by 60%. With the increasing of cryogenic treatment time, the dislocation morphology evolves from short linear shape to long curved shape and ring shape in turn, and the dislocation density increases significantly. Al1.4CrFe2Ni2 HEA exhibits excellent mechanical properties (480 HV hardness and 3107 MPa fracture strength) after cryogenic treatment for 24 h, which increase 9.1% and 24.33% than the matrix alloy (440 HV and 2499 MPa) while maintain high fracture strain, up to 40.8%. This is attributed to the volume shrinkage and lattice distortion superposition of HEAs cause the extrusion effect between grains. Under the effect of cryogenic treatment, the internal stress increased with volume shrinkage and the dislocation strengthening obviously.