Microstructure and texture of severely warm-rolled and annealed coarse-grained CoCrNi medium entropy alloy (MEA): A perspective on the initial grain size effect

Abstract

Microstructure and texture formations were investigated in a coarse-grained starting material (average grain size ~100 µm) of equiatomic CoCrNi MEA after severe warm-rolling and annealing. The results were compared with a fine-grained starting material (FGSM with average grain size ~7 µm) to highlight the effect of starting grain size. Progressive microstructural evolution accompanied by deformation bands, shear bands, and nano-twins formation resulted in an ultrafine microstructure in the heavily warm-rolled CGSM. The hardness of CGSM after 90% warm-rolling was similar to FGSM, indicating a rather comparable ultrafine microstructure. The deformation texture of the CGSM was rather similar to the FGSM featured by a weak brass component. Remarkably, the annealed grain sizes of the CGSM and FGSM series of specimens were rather similar. These observations amply corroborated with comparable deformation microstructure in the two materials. Both CGSM and FGSM showed weak recrystallization texture featured by the retention of deformation texture components. The results indicated rather limited effect of the starting grain size on microstructure and texture formation in warm-rolled and annealed CoCrNi MEA. Further, a remarkable strength-ductility balance could be obtained in annealed CGSM due to ultrafine microstructure and solid solution strengthening.