Probing deformation mechanisms of CoCrFeNiMn0.75Cu0.25 highentropy alloy after thermo-mechanical treatment using in situ EBSD investigation

Abstract

In this study, the CoCrFeNiMn0.75Cu0.25 high-entropy alloy (HEA) was systematically investigated to elucidate the effects of different annealing temperatures on the microstructure and mechanical properties of the face-centered cubic (fcc) structural alloy, renowned for its exceptional strength-ductility synergy. After annealing at 1273K, the HEA possesses an excellent combination of high strength (∼700 MPa) and high plasticity (∼45 %). This work establishes a temperature-dependent microstructural evolution mechanism in CoCrFeNiMn0.75Cu0.25 HEA, focusing on the Cr-rich precipitation and annealing twin formation. At lower annealing temperatures (973K), the precipitations impede dislocation motion, thereby enhancing the yield strength of HEA. In contrast, at higher annealing temperatures (1273K), the alloy develops a microstructure dominated by high-angle grain boundaries (HAGBs) (∼92 %) with abundant annealing twins. In-situ electron backscatter diffraction (EBSD) characterization was conducted on the 1073K and 1273K annealed samples to analyze microstructural evolution during tensile deformation. The plastic deformation of the rolled alloy after annealing at 1073K (CRA-1073K) is primarily governed by dislocation slip, characterized by a high slip band density and a rapid slip band expansion rate. In contrast, the CRA-1273K sample exhibited a lower initial slip band density and slower propagation rate in the early deformation stages. By leveraging in-situ EBSD characterization, this study not only elucidates the strengthening mechanisms and microstructural evolution of CoCrFeNiMn0.75Cu0.25 HEA, but also demonstrates the novelty of capturing real-time microstructural responses–such as slip band formation and twinning–during deformation. These insights provide a solid foundation for optimizing thermomechanical parameters to achieve a desirable strength-ductility synergy.

Keywords

• High-entropy alloys
• Thermo-mechanical treatment
• In-situ EBSD
• Strength-ductility synergy
• Microstructural evolution