Nanoscale Characterization of Elemental Partitioning between Gamma and Gamma Prime Phases in Rene 88 DT Nickel-Base Superalloy

The chemical partitioning of alloying elements between the disordered gamma and ordered gamma' phases in the nickel-base superalloy Rene 88 DT, has been characterized in detail using three-dimensional atom probe tomography (3DAP) coupled with energy filtered transmission electron microscopy (EFTEM) studies. After a homogenization treatment followed by a water quench, it is observed that the morphology of the gamma' precipitates remains near spherical even after long aging times. Compositional variation, observed between small (< 5 nm) and larger gamma' precipitates, reduces with increasing aging time, while the compositional gradient across the gamma/gamma' interface decreases. The process of growth of c gamma' precipitates seems to occur through coalescence of adjacent gamma' precipitates, facilitated through the formation of necks'' between adjacent precipitates. These necks are observed to have intermediate elemental concentration values between the matrix and the gamma' precipitate compositions.