The metallurgical structure of Inconel 718 is complex due to the precipitation of phases c0 ; c00 and d in the main austenitic structure of the c phase. The c0 ; c00 and d phases are an ordered structure however the c phase is a disordered lattice. In this section, we are focusing on the carbides precipitation process in the grain boundaries which could lead to material fracture if improper morphology appears during the fabrication process.
Carbon element precipitates with Chrome, Titane and Niobium to form primary carbide of type MX (M = Nb, Ti, . . .) and (X = C, N) such NbC or TiC located in grain boundaries. It is a B1 cubic stable structure at high temperature and it is not affected by post heat treatment (up to 1250