Effect of Heat Treatment Process on Recrystallization of Directional-Solidified Superalloy 4777DS

Abstract:

The effects of different heat treatment processes, alloy states, and stress relief annealing processes on recrystallization defects in 4777DS superalloy were studied using SEM and EBSD. SEM observation shows that the γ′ phase near the surface of the sandblasted sample undergoes deformation, changing from an initial butterfly shape to a long strip distribution on the alloy surface. The observation of recrystallization of the alloy after insulation at different heat treatment temperatures shows that the temperature at which recrystallization occurs is 1055 ℃. When the heat treatment temperature is higher than the dissolution temperature of the γ′ phase, recrystallization presents an equiaxed morphology, while when the heat treatment temperature is lower than the dissolution temperature of the γ′ phase, it presents a cellular recrystallization morphology. With the prolongation of heat treatment time, the proportion of large angle grain boundaries decreases, and the resulting annealing twins help to reduce distortion energy. A comparison of recrystallization behavior under different initial alloy states reveals that the as-cast alloy exhibits the highest tendency for recrystallization. In line with practical engineering requirements, a shorter annealing time can effectively reduce the recrystallization degree of alloys.