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.
Highlights
The blades operating in the turbine hot section of jet engines must be resistant to, among others, high thermomechanical loads
The inserts on the right side show exemplary hour-like shapes that visualize single dendrites on the fragments of the L and R surfaces. These shapes were created by oblique cuts through the dendrites by the planes of the R and L surfaces, which means that the primary dendrite arms grew non-precisely parallel to those planes
Local changes in the α and β angles of the primary crystal orientation and the γ angle of the secondary crystal orientation occur in areas 3–4 mm in width located near the side wall of the blade cooling bores. These changes are caused by the different alignment of both the primary and secondary dendrite arms, depending on their distance from the cooling bores
Summary
The blades operating in the turbine hot section of jet engines must be resistant to, among others, high thermomechanical loads. For this reason, turbine blades are made of heat and creep-resistant materials such as the most recently used single-crystalline. The blades are produced with cooling channels or bores to reduce their temperature. The single-crystalline (SX) CMSX-4 blades are capable of maintaining high mechanical and fatigue strength, and in particular, high-temperature creep resistance throughout their entire service life [1,2,3,4]. Even a slight increase in the service life of the blades can significantly reduce the operating costs of new generation turbo-jet engines. Understanding the mechanisms that create heterogeneity in the blade structure during crystallization may lead the way to the improvement of the production process, and to an amelioration of the economic factors
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