Hierarchical structure and remarkable properties of the CoCrFeNiCu high entropy alloy produced by fast mechanical synthesis and spark plasma sintering

Bulk CoCrFeNiCu-based high entropy alloy was fabricated using a combination of short-term high energy ball milling and rapid spark plasma sintering. Extensive studies by using x-ray diffraction, scanning and transmission electron microscopy, alongside with energy-dispersive and electron energy loss-spectroscopies revealed that the fabricated material possesses a unique hierarchical structure. The structure involves a multicomponent Cu-depleted fcc-solid solution with extremely thin (∼ 1–10 nm) layers of the Cu-based phase, primarily located on the grain boundaries. In addition, Cr ₂O ₃ nano-precipitates are uniformly distributed throughout the grain volume. Such complex hierarchical structure contributes to the unique material properties: yield strength 1205±20 MPa, bending strength 1362±62 MPa and Vicker’s micro hardness 4.86 ± 0.63 GPa. Nano-hardness and reduced modulus measured by nano-indentation provided values of 6.3±0.2 GPa and 160±3 GPa, respectively. Furthermore, the alloy was found to exhibit ferromagnetic properties. The results obtained were compared with previously reported data, and the details of the fabrication process and how it impacts the material properties were discussed.