Softening mechanisms activated during high-strain hot compressive deformation of as-cast AlCoCrFeNi2.1 eutectic high entropy alloy

The intricate structures present in as-cast eutectic high-entropy alloys (EHEAs) have not yet been completely elucidated, particularly regarding the softening mechanisms that become active during high-temperature deformation. The present work investigates the potential roles of several micro-mechanisms, such as dynamic fragmentation of dendritic and inter-dendritic (eutectic) regions, spheroidization, and the dynamic restoration processes of the constituent phases in an as-cast AlCoCrFeNi_2.1 equiatomic high-entropy alloy. To evaluate the potential occurrence of the mentioned micro-mechanisms, multiple interrupted compression tests were performed at 1000℃ during various softening stages of deformation, and the resulting microstructures were examined in detail. In conjunction with the stress exerted by dislocation accumulation on the lamellar B2 phases, the intensified chemical potential gradients between constituent phases stemmed from the as-cast microstructure serve as the motivating factor for the spheroidization of the lamellar B2 phase. Interestingly, the hot deformed microstructure is prone for continuous and progressive substructure development, which drives fragmentation in the primary FCC dendrites. Alongside of phase fragmentation, as deformation proceeds, the capability for development of progressive cell structure culminates in the process of continuous dynamic recrystallization, recognized as a significant factor influencing the softening behavior of the alloy.