Deformation induced intermediate metastable lattice structures facilitate ordered B2 nucleation in a fcc-based high entropy alloy

<p>Ordered B2 precipitates typically nucleate at the grains-boundaries of <i>fcc</i>-based high entropy alloys. Here, we report a novel mixed-mode coupled displacive-diffusional transformation resulting in homogeneously distributed intra-granular B2 precipitates within the <i>fcc</i> matrix. Severe plastic deformation forms compositionally invariant, metastable distorted <i>fcc</i> structures, resembling hexagon-like templates, at the deformation twin-boundaries. These shear-induced hexagon-like templates correspond to the symmetry of the {111}<i><sub>bcc</sub></i> planes, and act as sites for B2 nucleation, establishing the <i>fcc-bcc</i> Kurdjumov–Sachs (KS) orientation relationship. However, the composition of these B2 precipitates is far-from-equilibrium. Subsequent isothermal annealing causes solute partitioning driving the composition of the B2 precipitates towards equilibrium.</p> <p>For the first time, a mixed mode displacive-diffusional <i>fcc</i>-to-<i>bcc</i>-ordered B2 transformation mechanism was revealed in a deformed <i>fcc</i>-based Al<sub>0.3</sub>CoCrFeNi complex concentrated or high entropy alloy.</p>