Effect of Short-Term Aging Treatment on γ' Phase Precipitation Behavior in DD6 Single Crystal Superalloy

The effects of different cooling speeds on the microstructure evolution of second-generation nickel-based single crystal superalloy DD6 were revealed by high-resolution transmission electron microscopy and scanning electron microscopy. Results show that under air-cooling conditions a large number of secondary gamma' precipitates are distributed at the matrix channels. The secondary gamma' precipitates progressively evolve from spherical to cuboidal and then to butterfly-like shapes. And the size also increases with time. Sharp crevices appear at the edges of the gamma' precipitates and gradually evolve into serrated grooves. Under furnace-cooling conditions, a large number of fine spherical secondary gamma' precipitates are distributed in the collective channel, and the width of the matrix channel decreases and is negatively correlated with the holding time. Under water-cooling conditions, there is no secondary gamma' precipitate in the matrix channel. The cubicity of gamma' precipitates is complete, and there is no significant change in morphology with the prolongation of the holding time. gamma' precipitates produce a large number of positive-negative edge-type dislocations between the two-phase interfaces in the process of selective decomposition. The positive-negative edge-type dislocations on the two sides of the phase boundary meet, producing annihilation, which reduces the surrounding energy and promotes the selective decomposition of the gamma' precipitates.