Intragranular precipitation in alloy 718

A combined energy-compensated 3-dimensional atom probe and transmission electron microscope characterization has been performed to determine the nature of the intragranular precipitates that form in Alloy 718 after various stages of a multistage heat treatment. Primary gamma " precipitates were found to form after the 870 degrees C stage. The secondary precipitates formed at lower temperatures were not found to be uniform throughout their volume, but to be divided into two distinct regions enriched in either niobium, or in aluminum and titanium, that are characteristic of the gamma " and gamma' phases, respectively. The experimentally determined partitioning data of the solute elements between the gamma matrix and the gamma " and gamma' phases was found to agree with the trends in the thermodynamic predictions. (C) 1999 Elsevier Science S.A. All rights reserved.