View article

The paper reports evolution of two-phase microstructure quantitatively in a high entropy alloy of composition Co_37.6Ni_35.4Al_9.9Mo_4.9Cr_5.9Ta_2.8Ti_3.5. A very high-volume fraction of ordered L1₂ precipitates forms below its solvus temperature of 1156 °C that cannot be suppressed during quenching. The quench microstructure contains nanometric bimodal size distribution of spheroidal and irregular precipitates, both having L1₂ ordering (γ’) and a Co + Ni concentration close to 75 at. %, thus representing a stoichiometry of (Ni,Co)₃ (Al,Cr,Ta,Ti,Mo). The alloy shows hardening on aging with a peak in hardness value at 900 °C for 50 h of annealing. The morphology of the precipitates at this stage evolves into cuboidal shape having rounded corners with a lattice mismatch of +0.22% with the matrix. A detailed study of the coarsening behaviour of these precipitates in the matrix of complex solid solution indicates that …