The effect of aging temperature and time on nano-lamellar structure formation and tensile properties in Al₁₀(CoFeNi_1.5)₉₀ high entropy alloy

Structural materials with high strength and good ductility are required by the aerospace, automotive and energy sectors. The high strength and high ductility are limited in conventional alloys due to their simple composition (two or three base elements) and well-defined microstructure (depending on the metallic base element). As a solution to this difficult challenge, we have proposed a novel strategy to design HEAs using the eutectoid nano-lamellar microstructure concept, i.e. composed of alternative lamellar phases of soft face-centered cubic (FCC) and hard body-centered cubic (BCC), both with precipitates. Here, the eutectoid nano-lamellar microstructure composed of FCC+L12 and BCC+B2 in Al₁₀(CoFeNi_1.5)₉₀ HEA is a result of the solid-state decomposition of the single-phase recrystallized FCC matrix during heat treatment between 500 °C and 600 °C. The aging temperature is directly related to the reciprocal of the nano-lamellar thickness and the yield strength is directly correlated to the inverse square root of the lamellar. The ultimate tensile strength and ductility measured after aging at 500 °C, 550 °C, 575 °C and 600 °C are 1530.38 ± 57 MPa and 0.99 ± 0.1 %, 1509.80 ± 23 MPa and 1.31 ± 0.15 %, 1585.56 ± 5 MPa and 8.57 ± 1 %, and 1135.95 ± 8 MPa and 24.30 ± 2 %, respectively. Such tunability of microstructures and mechanical properties in the multi-component HEA is due to lattice distortions and diffusion during thermo-mechanical processes.