Abstract
The areas located near the cooling bores of single-crystalline cored turbine blades made of nickel-based CMSX-4 superalloy were studied. The blades were solidified by the vertical Bridgman technique in the industrial ALD furnace. Longitudinal sections of the blades were studied by Scanning Electron Microscopy, X-ray diffraction topography, X-ray diffraction measurements of the γ′-phase lattice parameter a, and the α angle of the primary crystal orientation. The local changes in α were analyzed in relation to the changes of the dendrite’s growth direction near the cooling bores. It was found that in the area approximately 3 ÷ 4 mm wide around the cooling bores, changes of α and a, both in the blade root and in the airfoil occurred. The local temperature distribution near the cooling bores formed a curved macroscopic solidification front, which caused changes in the chemical composition and, consequently, changes in the a value in a range of 0.002 Å to 0.014 Å. The mechanism of alloying elements segregation by tips of the dendrites on the bent solidification front was proposed. The multi-scale analysis that allows determining a relation between processes proceed both on a millimeter-scale and a micrometric and nanometric scale, was applied in the studies.
Highlights
The nickel-based superalloys belong to the class of materials developed for high-temperature applications, i.e., for producing single-crystalline (SX) blades applied in high-pressure turbines for jet engines or electricity generators
The CMSX-4 belongs to the 2nd generation of SX superalloys, consist of cubic γ-phase in the form of the net of thin channels creating the matrix, located between γ0 cubic crystals playing a reinforcement role [1,2,3,4]
The dark bands marked by S1, S2, S3, and SB11 arrows can be used as an example
Summary
The nickel-based superalloys belong to the class of materials developed for high-temperature applications, i.e., for producing single-crystalline (SX) blades applied in high-pressure turbines for jet engines or electricity generators. Due to the harsh operating conditions, the SX blades made of superalloys must have the ability to keep high strength, creep resistance, good hot corrosion, and oxidation resistance during long-term service. One of the most widely-used nickel-based superalloys is CMSX-4. The CMSX-4 belongs to the 2nd generation of SX superalloys, consist of cubic γ-phase in the form of the net of thin channels creating the matrix, located between γ0 cubic crystals playing a reinforcement role [1,2,3,4]. The size of γ0 crystals is about 1 μm or less
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