Recrystallization of single crystal superalloy CMSX-4 casting

Abstract

Single crystal plate castings of superalloy CMSX-4 were prepared, providing simplified geometries of turbine blades featured with five stage platforms. The recrystallization behavior in the plate castings was investigated after solution heat treatments at different temperatures. The results show that after solution heat treatment, recrystallization occurs at the abrupt cross-section of every platform except the lowest one. The recrystallization area increases and then decreases as the platform's height increases. The outside platform of the casting is also more likely to result in recrystallization than the inside one. The nucleation and growth of the recrystallization grains are significantly influenced by the solution heat treatment temperature (TH). When TH is raised from 1303 ℃ to 1315 ℃, the recrystallization area increases by 30 times, from 9.7 mm2 to 293 mm2. Because of the abrupt section transition, the platform part of the casting will produce more plastic deformation and accumulate a large amount of deformation energy during solidification and cooling, and the abrupt change in cross-section will easily become the source of recrystallization during the subsequent heat treatment. Meanwhile, the difference in heat exchange conditions, cooling rate and deformation rate during solidification leads to uneven stress distribution. As a result, different recrystallization behaviors appear after solution heat treatment.Furthermore, increasing TH can effectively promote the dissolution of γ/γ' eutectics and coarse γ' phase, reduce the pinning effect of residual γ/γ' eutectics and coarse γ' phase in the recrystallization grain boundary migration process, and significantly increase the recrystallization defect area.

Keywords

• single crystal superalloy
• cmsx-4
• recrystallization
• plastic strain
• numerical simulation