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

摘要

The chemical partitioning of alloying elements between the disordered γ and ordered γ′ phases in the nickel-base superalloy René 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 γ′ precipitates remains near spherical even after long aging times. Compositional variation, observed between small (<5 nm) and larger γ′ precipitates, reduces with increasing aging time, while the compositional gradient across the γ/γ′ interface decreases. The process of growth of γ′ precipitates seems to occur through coalescence of adjacent γ′ 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 γ′ precipitate compositions.