Precipitation and clustering in the early stages of ageing in Inconel 718

In this report we investigate the onset and evolution of precipitation in the early stages of ageing in the alloy WE 91, a variant of the Ni–Fe–Cr superalloy Inconel 718 (IN718). Transmission electron microscopy and atom probe tomography were used to study the size and volume fraction of γ′ and γ″ precipitates and the extent of pre-precipitate clustering of Al/Ti and Nb.Co-located γ′ and γ″ precipitates were observed from the shortest ageing times that precipitates could be visualised using atom probe. At shorter times, prior to the observation of precipitates, clustering of Al/Ti and Nb was shown to occur. The respective volume fraction of the γ′ and γ″ precipitates and the clustering of Al/Ti and Nb suggest that γ″ nucleates prior to γ′ during ageing at 706 °C for this alloy.

Research highlights▶ IN718 could be age hardened rapidly by secondary phase formation. ▶ Co-located phases were observed in the earliest stage of detection. ▶ Clustering of Ti/Al and Nb atoms was observed prior to precipitation.