Effect of Re Addition on the Sensitivity to Recrystallization in As-Cast Ni-Based SX Superalloys

The recrystallizationRecrystallization of nickel-based single-crystal superalloysNickel-based single-crystal superalloy during solution treatment may be promoted by local deformation induced during the cooling stage of directional solidificationDirectional solidification and is related to alloy chemistry. In this study, the effect of Re additionRe addition on the sensitivity to recrystallizationRecrystallization of nickel-based single-crystal superalloysNickel-based single-crystal superalloy and the ways in which Re affects nucleationNucleation and growth of recrystallized grainsRecrystallized grains are investigated using the as-cast alloy without Re additionRe addition and those with Re additionRe addition of 2 and 4 wt.%. It is suggested that 4 wt.% Re additionRe addition can significantly increase the propensity to nucleate recrystallized grainsRecrystallized grains but significantly inhibit grain growthGrain growth of the as-cast SX superalloySuperalloys. The former is attributed to the increase of Re segregationSegregation at the dendrite scale, which leads to the increase of strength difference in γ matrix of the dendrite core and interdendritic region, as well as the increase in eutectics and casting pores, thus providing higher stored energy and more nucleationNucleation sites for recrystallizationRecrystallization nucleationNucleation. Meanwhile, the severe Re segregationSegregation in γ matrix of high-Re alloys increases the γ′ solvus temperature and reduces the precipitatePrecipitates-free zone, thus inhibiting growth of recrystallized grainsRecrystallized grains. These insights will be beneficial to alloy designAlloy design and process optimization and allow further improvement of the casting costs.