The effects of Y pre-alloying on the in-situ dispersoids of ODS CoCrFeMnNi high-entropy alloy

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. 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 composition, leading to an increase in the Zener pinning forces on the grain boundary movement. ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K. This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultrafine-grained structure, resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.