Effect of starting grain size on the evolution of microstructure and texture during thermo-mechanical processing of CoCrFeMnNi high entropy alloy

The effect of starting grain size on the formation of microstructure and texture in heavily deformed equiatomic CoCrFeMnNi high entropy alloy (HEA) was investigated. For this purpose two alloys with average grain size -7 mu m (fine grained starting material or FGSM) and 200 mu m (coarse grained starting material or CGSM) were cold-rolled to 90% and 95% reduction in thickness and isochronally annealed for one hour at temperatures ranging from 700 degrees C to 1200 degrees C. Development of strong brass type texture, typical of low stacking fault energy (SFE) materials was noticed in both FGSM and CGSM. Near ultrafine microstructure formation was observed after annealing at 700 degrees C but extensive grain growth was observed only after annealing at 1200 degrees C. The FGSM showed finer grain size as compared to CGSM after heavy deformation and annealing. The annealing twin boundary fraction increased with increasing annealed grain size. The annealing textures of both FGSM and CGSM did not show strong dominance of the {236<385> or {113}<332> components unlike low SFE brass. Furthermore, the volume fractions of different annealing texture components of the HEA were not significantly affected by starting grain size or annealing temperature in stark contrast to low SFE brass. These differences could be explained on the basis of homogenously deformed matrix and sluggish diffusion in HEA which greatly reduced the preferential nucleation and growth of components, respectively. (C) 2015 Elsevier B.V. All rights reserved.