Microstructural evolution in adiabatic shear localization in Al0.4CoCrFeNi high-entropy alloy

Abstract

The microstructural evolution in adiabatic shear localization in Al0.4CoCrFeNi high-entropy alloy (HEA) was examined through a forced shear technique by a split Hopkinson pressure bar (SHPB) using hat-shaped specimens. The TEM results show that the elongated and parallel grains are the major characteristics of the transition region. The central region of the adiabatic shear band (ASB) is primarily composed of ultrafine and equiaxed recrystallized grains with sizes ranging from 50 to 250 nm, with a typical size of 100 nm. It is found that the plastic deformation of the majority of large grains (100–250 nm) is primarily mediated by dislocation slip. To effectively coordinate this deformation, twins with varying thicknesses were generated within the grains (50–100 nm) through cross-slip of dislocations and dynamic overlapping of four stacking faults (SFs) of dissociated dislocations, respectively. According to the classical one-dimensional Fourier heat conduction equation and recrystallization theory calculations, it is proved that ultrafine and equiaxed recrystallized grains did not undergo significant growth during the cooling stage after deformation. The thermodynamics and kinetics calculated results indicate that instant grain refinement within the ASB is due to the rotational dynamic recrystallization (RDR) that occurs during the deformation process.