Defect structure and hardness in nanocrystalline CoCrFeMnNi High-Entropy Alloy processed by High-Pressure Torsion

Abstract

An equiatomic CoCrFeMnNi High-Entropy Alloy (HEA) produced by arc melting was processed by High Pressure Torsion (HPT). The evolution of the microstructure during HPT was investigated after 1/4, 1/2, 1 and 2 turns using electron backscatter diffraction and transmission electron microscopy. The spatial distribution of constituents was studied by energy-dispersive X-ray spectroscopy. The dislocation density and the twin-fault probability in the HPT-processed samples were determined by X-ray line profiles analysis. It was found that the grain size was gradually refined from similar to 60 mu m to similar to 30 nm while the dislocation density and the twin-fault probability increased to very high values of about 194 x 10(14) m(-2) and 2.7%, respectively, at the periphery of the disk processed for 2 turns. The hardness evolution was measured as a function of the distance from the center of the HPT-processed disks. After 2 turns of HPT, the micro hardness increased from similar to 1440 MPa to similar to 5380 MPa at the disk periphery where the highest straining is achieved. The yield strength was estimated as one-third of the hardness and correlated to the microstructure.