In Situ Neutron Diffraction Investigating Microstructure and Texture Evolution upon Heating of Nanostructured CoCrFeNi High-Entropy Alloy

Herein, in situ temperature-dependent neutron experiments investigate the microstructural evolution of additively and conventionally manufactured CoCrFeNi high-entropy alloys, as-received, and after grain refinement through high-pressure torsion. The evolution of texture after grain refinement and during heating is consistent with typical fcc metals. Both conventional and modified Williamson-Hall analyses reveal that major contributions of microstresses stem from dislocations. For the nanostructured material, three temperature regimes are identified on a heating ramp, namely, stress recovery up to 800 K, followed by recrystallization at 850-960 K, and normal grain growth above, in line with the physical change of hardness increase on recovery, decrease on recrystallization, and cutback to the as-manufactured values after grain growth. The as-printed material exposes higher dislocation density than as-cast, reducing slightly upon heating, while there is limited temperature dependence on the lower dislocation density of the as-cast specimen. Stored energies have been elaborated for residual stress and Bauschinger contributions, dislocation energy, grain boundary amounts, and vacancy contents with scenarios of vacancy expulsion leading to recrystallization. Ultimately, the fully recrystallized nanostructured material shows the lowest dislocation density, which may render a recipe for stress release in additively manufactured materials.