Investigation of nano-scale precipitates in the CoCrFeMnNi high-entropy alloy processed by high-pressure torsion

Abstract

The influence of high-pressure torsion (HPT) at room and elevated temperatures on the structureof the high-entropy alloy CoCrFeMnNi has been investigated. Dynamic processes of phasetransformation, including solid solution decomposition and dispersion particle precipitation, havebeen identified. The microstructure of CoCrFeMnNi was studied using transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD).The kinetics of phase transformations was investigated by differential scanning calorimetry (DSC).As a result of deformation twinning processes in the HPT process at room temperature, there is asignificant grain refinement of the structure of the studied HEA to nanocrystalline size of 50 nm. Inturn, during the HPT process at 300 °C, the dynamic recovery process with the decomposition of thesolid solution begins. As a result, it was found that the increasing temperature of HPT leads to theformation of UFG structure with a grain size of ~400 nm. At the same time, nano-scale precipitatesconsisting of the following phases are formed in individual grains: Cr-rich BCC phase and tetragonalσ-phase with variable phase composition. The size of the precipitates reaches up to 10 nm with avolume fraction of less than 3%.