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 gamma' and gamma '' precipitates and the extent of pre-precipitate clustering of Al/Ti and Nb. Co-located gamma' and gamma '' 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 gamma' and gamma '' precipitates and the clustering of Al/Ti and Nb suggest that gamma '' nucleates prior to gamma' during ageing at 706 degrees C for this alloy. (C) 2010 Elsevier B.V. All rights reserved.