Effects of Solutioning on the Dissolution and Coarsening of γ' Precipitates in a Nickel-Based Superalloy

The dissolution and the coarsening of the gamma' precipitates in a nickel-based superalloy GTD-111 solutionized under various solution heat treatment conditions were investigated. The gamma' solvus temperature for the GTD-111 superalloy was about 1180.79 A degrees C obtained by differential scanning calorimetry test. The dissolution and the coarsening of gamma' in the dendrite core were simultaneously observed, but the gamma' precipitates in the interdendritics only occurred to coarsen under the condition of 1125 A degrees C/2 h. The gamma' dissolution, including dendrite core and interdendritics, gradually played a dominant role in the competition between the dissolution and the coarsening of gamma' during the solutioning with the increase of solution temperature and holding time, indicating that the elastic strain field of the alloy gradually reduced. The solution condition of 1225 A degrees C/6 h or 1250 A degrees C/2 h was the optimal solutioning schedule than the other schedules. For a lower solution temperature, the volume fraction of primary gamma' precipitates can faster reach its equilibrium value which is larger than that for a higher solution temperature. With the increase of holding time, the gamma' dissolution rate continuously decreased, and the dissolution activation energy of gamma' gradually increased.