Superior high tensile elongation of a single-crystal CoCrFeNiAl_(0.3) high-entropy alloy by Bridgman solidification

摘要

The crystallographic orientation, tensile behavior, fracture mechanism, hardness, and elastic modulus of a single-crystal CoCrFeNiAl_(0.3) 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 σ_y = 171.65 + 0.73/ d~(1/2). 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.