Strengthening Al0.1CoCrFeNi high-entropy alloy via multiaxial cryogenic forging and low temperature annealing

Face-centered cubic (FCC) high-entropy alloys (HEAs) exhibit excellent fracture toughness and fatigue properties at both ambient and cryogenic temperatures. However, the relatively low strength of FCC HEAs at room temperature limits their widespread application. Herein, we present a novel approach to tailoring the microstructure of the Al0.1CoCrFeNi HEA and improving its room temperature tensile strength through multiaxial cryogenic forging (MACF) and low temperature annealing (LTA). After the treatments, the tensile strength increases from 687 MPa for the as-prepared fine-grained HEA to 1487 MPa for the MACF specimens annealed at 673 K for 48 h. Our analysis indicates that the strengthening mechanisms are twofold: the tensile strength increased by about 455 MPa after the MACF treatment, which is due to the synergistic effect of dislocations and nanotwins; after LTA, the tensile strength abnormally increased by about 345 MPa, which can be attributed to stacking faults, hexagonal close-packed, and 9R structures formed by thermal relaxation of nanotwin boundaries.