Recrystallization mechanism for the grain refinement in undercooled DD3 single crystal superalloy

The microstructure evolution of DD3 single crystal superalloy undercooled to 210 K is systematically investigated by employing compound molten salt purification combined with the thermal cycle in high vacuum. When undercooling is beyond 153 K, the dendrite distortion and disintegration take place, and then a kind of complete quasi-spherical equiaxed crystal structure is obtained as the critical undercooling ΔT* (180 K) is reached. In connection with the observation in the behavior of the crystalline defects, such as dislocation, during the refinement process, it is consequently concluded that the grain refinement above the critical undercooling can be attributed to the recrystallization mechanism.