Preparation of nanostructured CoCrFeMnNi high entropy alloy by hot pressing sintering gas atomized powders.

Pre-alloyed CoCrFeMnNi high-entropy alloy (HEA) powders were prepared by gas atomization and consequently hot pressing sintered (HPS) at 1100 °C for 2 h for fabrication bulk materials. Sintered equiatomic CoCrFeMnNi HEA exhibited a homogeneous FCC structured single-phase solid solution and equiaxed grains with an average size of ∼16 µm. Analyses using TEM showed that sheet-like metastable structures with a size of ∼55 to 160 nm were formed in the sintered bulks. The nano-sized metastable structures were inherited from the gas atomized CoCrFeMnNi powders with nano-sized crystallites formed during the rapid solidification process. The room temperature yield and ultimate tensile strength of sintered HEA reached 358 and 778 MPa, respectively, and the alloy kept excellent plasticity of ∼28 %. Investigations of the deformation substructures at specific strain levels with EBSD revealed the sintered CoCrFeMnNi HEA kept FCC structured single phase and the main deformation mechanism was dislocation slip. The strengthening mechanism can be attributed to the combination effects of grain refinement and the presence of nano-sized metastable structures.