Impact of heavy warm-rolling on microstructure and properties of an extremely low stacking fault energy high entropy alloy

Abstract

This research focused on the influence of heavy (∼90 % reduction in thickness) warm-rolling (WR) on the microstructure, texture, and mechanical properties of an extremely low stacking fault energy (SFE) Co₂₀Cr₂₆Fe₂₀Mn₂₀Ni₁₄ high entropy alloy (HEA). The findings were further contextualized by comparing the results with heavy cold- (CR)/cryo-rolled (CryoR) low SFE alloys suitably. The WR was carried out at 650 °C up to 90 % thickness reduction, resulting in the formation of various microstructural features like dislocation cells (sub-structures), deformation twins, shear bands, precipitation of Cr-rich σ-phase, and a deformation-driven banded nanostructure with a remarkably fine inter-lamellar spacing of 130 ± 30 nm. Additionally, WR led to the development of a predominant brass-type texture. Annealing resulted in fully recrystallized fine microstructures up to 950 °C due to the presence of σ precipitates inhibiting grain growth; however, beyond which, the precipitates were dissolved and stimulated significant grain growth. The annealing textures showed the retention of weak α-fiber (ND//<110>) components and a high-volume fraction of random components, presumably due to the absence of dominating preferential nucleation or preferential growth mechanisms. An appreciable balance in strength-ductility (∼1 GPa-20 %) was achieved in the WR-processed HEA due to fine recrystallized grain size and large fraction of in-grain precipitates, which compared favorably with several other HEAs. Therefore, WR could be an attractive processing strategy for engineering the microstructure and properties of the low SFE HEAs.