Dynamic recrystallization in AlXCoCrFeNi duplex high entropy alloys

Most of the applications planned for high entropy alloys (HEAs) entail thermomechanical processing. In the current study, the hot deformation and dynamic restoration mechanisms of two duplex high entropy alloys (Al0.6CoCrFeNi and Al0.9CoCrFeNi) are revealed through a detailed electron back-scattered diffraction and transmission electron microscopy study. A standard homogenization of the cast microstructures results in face-centred cubic/body-centred cubic (FCC/BCC) duplex structures for both alloys. Al0.6CoCrFeNi has an FCC matrix containing dispersed BCC particles surrounded by interdendritic BCC. Al0.9CoCrFeNi has a BCC matrix with allotriomorphic and intragranularly dispersed FCC particles. Hot deformation at 1030 °C under the strain rate of 0.1s−1 is mainly accommodated through the matrix phase in both alloys. In Al0.6CoCrFeNi alloy, the FCC matrix undergoes discontinuous dynamic recrystallization mechanism (DDRX) while there are also some local observations of subgrain coalescence. DDRX mainly occurs at the interphase boundary mantle regions through the formation of Σ3 boundaries and the propagation of multiple twinning chains. Dislocations within the hot deformed FCC matrix have a large screw component. In the Al0.9CoCrFeNi alloy, the BCC matrix softens through continuous dynamic recrystallization (CDRX), characterised by the progressive conversion of low-misoriented subgrains into (sub)grains delineated partly by low-angle and partly by high-angle boundaries. Dislocations within the BCC matrix have a mixture of edge and screw character. The dispersed second phases in both alloys are mechanically fragmented during hot deformation and are quite evenly distributed throughout the microstructure at a strain of 1.5. •Softening mechanisms in Al0.6CoCrFeNi and Al0.9CoCrFeNi alloys were studied.•The FCC matrix undergoes discontinues dynamic recrystallization in the Al0.6 alloy.•DDRX occurs at the interphase boundary mantle regions through the formation of Σ3 boundaries.•In the Al0.9 alloy, the BCC matrix softens through continuous dynamic recrystallization mechanism.•The dispersed second phases in both alloys become mechanically fragmented during hot deformation.