Elemental Partitioning Associated with Different Generations of Gamma Prime Precipitates in Rene 88DT Nickel Base Superalloy (Preprint)

Abstract : The compositional and microstructural evolution of different generations of precipitates of the ordered gamma-prime phase during the continuous cooling, followed by isothermal aging, of a commercial nickel base superalloy, Rene 88DT, has been characterized by three dimensional atom probe tomography (3DAP) coupled with energy-filtered transmission electron microscopy studies. After solutionizing in the single gamma phase field, during continuous cooling at a relatively slow rate (approx. 24 degrees C/min), the first generation primary gamma-prime precipitates, forming at relatively higher temperatures, exhibit nearequilibrium compositions, while the smaller scale secondary gamma-prime precipitates, forming at lower temperatures, exhibit nonequilibrium compositions often consisting of excess Co and Cr, while being depleted in Al and Ti content. The compositions of the gamma matrix near these precipitates also exhibit similar trends with the composition being closer to equilibrium near the primary precipitates as compared to the secondary precipitates.