Oxide Dispersoid Strengthened CoCrFeMnNi High-Entropy Alloy: The Effects of Y2O3 Addition and Y Alloying

Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys (ODS-HEAs) were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties. Systematic microstructural analysis was carried out by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), high-resolution transmission electron microscopy (HRTEM), atom probe tomography (APT), and small-angle neutron scattering (SANS). Cryo-milled powder analysis, grain structure evolution after spark plasma sintering, dispersoid characteristics, and matrix/dispersoid interface structure analysis of the in-situ and ex-situ dispersoids within the high-entropy alloy (HEA) matrix were performed. In-situ and ex-situ dispersoid formations were observed in the Y2O3-added ODS-HEA, whereas the in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical compositions. In-situ oxide dispersoids enhance the construction of ultrafine-grained structures up to approximately 300 nm in diameter. This study shows that the pre-alloying method, in which yttrium is alloyed, is efficient in achieving fine coherent dispersoids with an ultrafine-grained structure, resulting in a significant enhancement of the tensile strength of the CoCrFeMnNi HEA.