Withdraw speed and anisotropic effects on the ultra-high temperature creep behavior of CMSX-4 Plus (SLS) single crystal Nickel-based superalloy

In this study, CMSX-4® Plus (SLS) single crystal nickel-based superalloy developed by Cannon-Muskegon Company was used, while different withdraw speed, 60 mm/h or 180 mm/h, in single crystal casting as a process parameter. After solid solution and aging heat treatment procedures according to the company’s specifications, single crystal specimens were subjected to microscopic analyses and high temperature creep test. Results show that the misorientation of single crystal grains under different process parameters is less than 5°, however, as the withdraw speed increases, the primary and secondary dendrite arm spacings of dendritic structure were reduced, which is consistent with the predicted changes in the theoretical model. The γ' particles, γ/γ’ eutectic phase, and element segregation in dendritic structure also changed with the withdraw speed. The particle size of γ' precipitates at 60 mm/h withdraw speed after heat treatment is relatively larger and uneven distributed, which also shows serious elemental segregation. After creep rupture, the rafting microstructure of 60 mm/h withdraw speed shows a wide γ/γ’ spacing, which could worsen the blocking of dislocation movement. These reasons deteriorate the anti-creep property of 60 mm/h withdraw speed specimens. In this study, specimen with 180 mm/h withdraw speed shows a uniform microstructure and less elemental segregation, which becomes the optimal process parameter. The pole figure with suggested regimes of stress rupture lives for old single crystals at low temperature is still valid for both CMSX-4 (SLS) and CMSX-4 Plus (SLS) single crystals at ultra-high temperature range.