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

An investigation of the grain refinement in the bulk undercooled DD3 single-crystal superalloy is performed. The application of a molten salt denucleating technique combined with thermal cycle enables such investigation over a wide range of undercooling up to 210 K. The microstructure formation has been discussed with respect to undercooling, nucleation and recalescence as well as recrystallization during recalescence and post-recalescence, respectively. Furthermore, TEM and SEM techniques are employed to reveal the recrystallization mechanism for grain refinement occurring at the critical undercooling ΔT*, and to explain the influence of Υ′ precipitation and solute segregation on the recrystallization, i.e. grain-boundary migration process.