Microstructural origins of high-temperature properties of 3D printable CrCoNi-based ODS multi-principal element alloys

A new design strategy has been recently introduced in the field of alloys for high-temperature applications. Enabled by additive manufacturing (AM), it combines oxide-dispersion-strengthening (ODS) and multi-principal element alloy (MPEA) concepts further opening up a vast unexplored compositional space to develop new 3D printable structural materials. One of the new compositions, an AM produced CrCoNi-based ODS-MPEA called GRX-810, exhibits extraordinary tensile strength, oxidation resistance and over 1000-fold better creep performance at temperature of 1093°C than the traditional polycrystalline wrought Ni-based alloys. The present study investigates origins of the high-temperature capabilities of GRX-810 through identification and detailed characterization of all relevant microstructural features and their evolution during creep, in direct comparison to the ODS-CrCoNi-ReB alloy. For the first time, a state-of-the-art multi-scale, multi-modal approach is used based on various high-resolution characterization techniques including high-energy synchrotron X-ray diffraction and the stereo-scanning transmission electron microscopy diffraction contrast imaging cross-correlated with energy dispersive X-ray spectroscopy. Detailed characteristics of oxide nanoparticle dispersoids were accurately quantified as well as the secondary phases both before and after creep testing. The evolution of the original hierarchical lattice defect substructures and the dislocation-dispersoid interactions was analyzed in detail for both alloys and correlated with the macroscopic creep response. The extensive datasets obtained via comparative analyses are discussed in context of conventional strengthening models to understand improved properties of GRX-810 alloy, and to provide guidelines for future design and optimization of 3D printable ODS alloys potentially enabling even higher temperature capabilities or specific service targeted performance abilities.