Recovery of cold-worked Al0.3CoCrFeNi complex concentrated alloy through twinning assisted B2 precipitation

Abstract

While the theory of recovery and recrystallization processes during annealing of pure metals and simple alloys is relatively well charted, systematic investigation of these processes in high entropy alloys or complex concentrated alloys (HEA/CCAs) is rather limited. The present paper focuses on the complex interplay between traditional recovery via dislocation annihilation, formation of annealing twins, and precipitation processes during isothermal annealing of a cold-worked candidate Al0.3CoCrFeNi HEA/CCA. While the cold-worked alloy contained a large number density of deformation twins, subsequent isothermal annealing resulted in a further increase in the fraction of Σ3 twin boundaries, which in turn acted as heterogeneous nucleation sites for ordered B2 precipitates. The heterogeneous microstructure obtained after isothermal annealing consists of coarse non-recrystallized FCC grains with high lattice curvature, and uniform distribution of B2 precipitates at prior grain boundaries, deformation bands and twins. The tensile yield stress increased with annealing time and this trend was attributed to the coupled effect of increasing fraction of Σ3 twin boundaries, and ordered B2 precipitates decorating these defects. After long-term annealing at 700°C the alloy exhibits an excellent combination of tensile yield stress ∼1010 MPa and ductility ∼15%, as well as substantial recovery of the strain hardenability.