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

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