Effects of dispersoid preforming via multistep sintering of oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy

Dispersoid formation and microstructural evolution in an oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy (HEA) using a newly designed multistep sintering process are investigated. The pro-posed multistep sintering consists of a dispersoid preforming heat treatment of as-milled 0.1 wt% Y2O3- CoCrFeMnNi high-entropy alloy powders at 800 degrees C, followed by sintering at 80 0-10 0 0 degrees C under uniaxial pressure. In the conventional single-step sintered bulk, the coarsened BCC Y2O3 dispersoids mainly form with an incoherent interface with the HEA matrix. In contrast, finer FCC Y2O3 dispersoids, an atypical form of Y2O3, are formed in the matrix region after multistep sintering. Nucleation of FCC Y2O3 disper-soids is initiated on the favorable facet, the {111} plane of the austenitic matrix, with the formation of a semi-coherent interface with the matrix during the dispersoid preforming heat treatment and it main-tains its refined size even after sintering. It is found that dispersoid preforming prior to sintering appears promising to control the finer dispersoid formation and refined grain structure.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.