The Influence of the Cooling Bores on the Dendritic Structure and Crystal Orientation in Single-Crystalline Cored CMSX-4 Turbine Blades

Abstract

Single-crystalline cored CMSX-4 blades obtained at a withdrawal rate of 3 mm/min by the vertical Bridgman method were analyzed. The dendritic structure and crystal orientation near the cooling bores of the blades were studied through Scanning Electron Microscopy, the X-ray diffraction measurements of α and β angular components of the primary crystal orientation, and the γ angular component of the secondary crystal orientation. Additionally, the primary arm spacing (PAS) was studied in areas near and far from the cooling bores. It was found that in the area approximately 3–4 mm wide around the cooling bores, changes occurred in the α, β, and γ angles, as well as in the PAS. The PAS determined for the transverse section of the root and the linear primary arm spacing (LPAS) determined for the longitudinal sections, as well as their relationship, have been defined for the areas located near the cooling bores and those at a distance from them. The vertical temperature gradient of 29.5 K/cm was estimated in the root areas located near the cooling bores based on the PAS values. The value of this gradient was significantly higher compared to the growth chamber operating gradient of 16 K/cm. The two-scale analysis applied in this study allowed for the determination of the relationship between the process of dendrite array creation proceeding on a millimeter scale, which is associated with the local changes in crystal orientation near the cooling bores, and that which proceeds on a scale of tens of millimeters, associated with the changes in crystal orientation in the whole blade cast.

Correlation between the Dendritic Structure and Lattice Parameter of γ′-Phase in Single-Crystalline Turbine Blades Made of Superalloys

“…The studies were aimed to determine the correlation between the lattice parameter a γ and the dendritic structure in the single-crystalline model blades made of the nickel-based superalloys by the Bridgman method using a spiral selector. The similar thematically results presented in our previous papers [37,45,46] were related to the macroscopic distribution of a γ and the dendritic structure studied in different types of as-cast CMSX-4 ® singlecrystalline blades by the X-ray diffraction methods. Changes in a γ (X) relation along the X segments of several tens of millimeters in length allowed to explain some details of the dendritic crystallization processes.…”

“…The distances between the segments representing so-called linear primary arm spacing (LPAS) were measured using the method described in Refs. [43,45]. The measurements with this method were performed using the scheme (Figure 2c) prepared by creating skeletal images.…”

Effect of secondary orientation on the microstructures in thin-walled castings of nickel-based single-crystal superalloys

“…In a study on the impact of thickness on the microstructure of turbine blades by Zhang et al [13], it was observed that PDAS diminished with decreasing wall thickness. Krawczyk and Bogdanowicz [14] also made a similar observation of nearby cooling bores in SX turbine blades. These regions with smaller PDAS around the cooling bores have a width of approximately 3-4 mm and have demonstrated the dependency of the PDAS on wall thickness.…”