Hot deformation mechanisms of dual phase high entropy alloys

Abstract

The microstructure of high entropy alloys can finally be designed via thermomechanical treatments to tune the mechanical properties. This work investigates the modification of the microstructure after treatments at 1100 °C for three hypo-eutectic high entropy alloys. Two phases were indexed according to the BCC and FCC crystal structures using electron backscattered diffraction. Their microstructure is investigated for three hot deformation tests: at a constant strain rate of 0.001s−1, at a strain rate jumps from 0.001s−1 to 1s−1 and from 1s−1 to 0.001s−1. The BCC size and fraction strongly influence the deformation of the FCC matrix. Due to its typical semi-interconnected hypo-eutectic structure, the BCC phase carries the load at the beginning of the deformation. Progressively, the FCC phase deforms to accommodate the plastic strain due to the bending and fragmentation of the BCC phase. Fine particles of the BCC phase are formed within the FCC matrix at high temperatures, and they pin the high-angle grain boundaries formed by continuous dynamic recrystallisation. The fragmentation of the BCC phase occurs faster for thinner eutectic BCC particles, and it is a consequence of I) the formation of boundaries during plastic deformation via dynamic recovery followed by continuous dynamic recrystallisation; II) the movement of phase boundaries consuming the formed boundaries within the BCC phase, fragmenting them. A fine substructure with a high density of high-angle grain boundaries is formed at 1100 °C for the alloy with initial fine BCC eutectic particles.