Superior high tensile elongation of a single-crystal CoCrFeNiAl0.3 high-entropy alloy by Bridgman solidification

The crystallographic orientation, tensile behavior, fracture mechanism, hardness, and elastic modulus of a single-crystal CoCrFeNiAl0.3 high-entropy alloy (HEA) successfully synthesized by Bridgman solidification are investigated in detail. The growth direction of the single-crystal product mainly focuses on the <001> orientation. An ultimate tensile elongation of about 80% is achieved in the single-crystal alloy, accompanied by a large work-hardening exponent and a shear-fracture mode. A quantitative Hall-Petch relationship for the current HEA can be obtained as σy=171.65+0.73/d. The single-crystal sample displays a relatively-lower elastic modulus than the as-cast counterpart, indicating the anisotropy of elastic modulus. The outstanding tensile ductility for the single-crystal product is attributed to (1) low-angle grain boundaries and thus less distance to dislocation motion; and (2) single <001> crystallographic orientation and therefore less plastic-strain incompatibility.