Nucleation burst in additively manufactured Inconel 718: 3D characterization of ISRO-induced equiaxed microstructure

The origin of isosahedral short range order (ISRO)-mediated nucleation in additively manufactured Inconel 718 is investigated in this work. 3D EBSD-EDS characterization of the equiaxed grain zone revealed a 5-fold symmetry axis emerging from the surface of a TiC particle. Using high resolution electron microscopy, the Nb2Ni and Ni6Nb7 phases have been identified around a TiC particle for the first time in this alloy. Such phases are associated with local Nb enrichment around the TiC particles. The Nb-rich liquid and the solidification conditions of the additive manufacturing process induce the formation of phases containing a high concentration of icosahedral clusters and are thought to be the origin of ISRO-mediated nucleation in this alloy.