Microstructures and Enhanced Mechanical Properties of an Oxide Dispersion-Strengthened Ni-rich High Entropy Superalloy Fabricated by a Powder Metallurgical Process

A Ni46Co22Al12Cr8Fe8Ti3Mo1 high entropy superalloy (Ni46 HESA) was fabricated by a powder metallurgical (PM) process. The composition of the alloy was determined through consideration of its PM processability. The alloy had a density of 7.82 g cm−3, which is lower than that of conventional Ni-base superalloys. The microstructure of the bulk alloy consisted of a face-centered cubic γ matrix and an L12 γ′ precipitate with minor amounts of Al2O3 and TiC inclusions. To leverage the advantages of PM processing, yttria (Y2O3) was added and dispersed in the HESA by mechanical alloying, which enhanced its mechanical properties via oxide dispersion strengthening. The oxide dispersion-strengthened Ni46 HESA containing 1 vol% of Y2O3 had a tensile yield strength of 1155 MPa at room temperature, 880 MPa at 700 °C, and 485 MPa at 800 °C. The excellent mechanical properties at room and elevated temperatures are attributed to solid solution strengthening, precipitation strengthening, dispersion strengthening, and grain boundary strengthening. The contribution of each strengthening mechanism was analyzed quantitatively using experimentally determined microstructural parameters.