Microstructural evolution and local mechanical properties of dendrites in Al0.6CoCrFeNi high entropy alloy

The microstructural evolution and local mechanical properties of dendrites, including the fcc dendritic core (DC) and bcc/B2 inter-dendritic (ID) regions of Al0.6CoCrFeNi high entropy alloy (HEA) at different annealing temperatures were investigated by electron microscopy and nanoindentation tests. In the fcc DC region, nanoparticles of the ordered L1(2) phase precipitated at 600 and 700 degrees C. At 800 degrees C, the L1(2) phase was replaced by a fine needle-like ordered B2 phase, and B2 coarsened with increasing temperature. In the bcc/B2 ID region, as the annealing temperature increases, the disordered bcc gradually transforms to the sigma phase, and the sigma phase stably exists at 700 and 800 degrees C. The nanoindentation test results showed that the L1(2), fine B2, and sigma phases significantly increased the hardness of the DC and ID regions. In addition, the solidification paths of the as-cast alloy and the phase evolution mechanisms in the DC and ID regions were explored in conjunction with thermodynamic calculations. The investigation of the structural evolution and mechanical behavior of different microscopic regions will facilitate HEA design.