The application of a molten-salt de-nucleating technique, combined with thermal cycling, permitted the as-solidified structure of the DD3 superalloy to be investigated over a wide range of undercoolings of up to 250K. The microstructure formation was discussed with respect to undercooling, nucleation and recalescence as well as recrystallization during recalescence and post-recalescence, respectively. Microstructure transition from the coarse-grained dendrites to the grain-refined equiaxed microstructures was observed in DD3 superalloy melt when ΔT > ΔT*. Furthermore, transmission electron microscopy and scanning electron microscopy technique were used to reveal the morphologies of crystal defects such as grain boundaries and dislocation, aiming at explaining recrystallization mechanism for grain refinement occurring beyond the critical undercooling, ΔT*, and demonstrating the influence of γ' precipitation and solute segregation on recrystallization.

Explanation of Grain Refinement by Direct Observation of Dislocation Morphology Evolution in Undercooled DD3 Superalloy. F.Liu, G.Yang: Materials Research Bulletin, 2002, 37[2], 365-75