Carbide Precipitation in Inconel 718

Abstract

The carbide phases occurring in Inconel 718 were studied with reference to their identity, distribution and morphology. It was found that the predominant carbide phase in this alloy is a niobium-rich MC phase. Carbide precipitation during ageing was observed to be confined exclusively to the austenite grain boundaries. The formation of intermetallic precipitate free zones (PFZ) in the vicinity of the carbide decorated grain boundaries was examined, and two distinct types of PFZ were noticed. The formation of these zones is discussed in light of solute depletion and vacancy depletion mechanisms. A time-temperature-precipitation diagram pertaining to carbide precipitation during ageing was constructed based on the microstructural observations made in this work. © 1993, Walter de Gruyter. Alle Rechte vorbehalten.