Effect of Sandblasting on Recrystallization Defects of Directional Solidification 4777DS Superalloys and Its Mechanism

The effects of different sand blasting processes on recrystallization defects and the occurrence of recrystallization in 4777DS alloy were studied using optical microscope and scanning electron microscope. The analysis of the recrystallization structure on the alloy surface after sandblasting shows that the depth of recrystallization on the alloy surface increases with the increase in sandblasting intensity, time, and gravel diameter, and the decrease in sandblasting distance. After sandblasting, the deformed sample shows that the γ′ phase near the sandblasted surface changes from a butterfly shape to a long strip shape, and some of the deformed γ′ phase surrounds the areas with greater deformation. At the same time, a large number of dislocations distributed in the γ matrix channels and γ′ phase are observed by TEM. The different γ′ phases between dendrites affect the growth of recrystallization, resulting in the formation of wavy grain boundaries. No inhibitory effect of eutectic or carbide on recrystallization has been found. Due to the small size of surface recrystallized grains and the presence of residual stress, a new layer of recrystallized grains will form in the subsurface.