The Low-Angle Boundaries Misorientation and Lattice Parameter Changes in the Root of Single-Crystalline CMSX-4 Superalloy Blades

Abstract

The relationship between the angles of misorientation of macroscopic low-angle boundaries (LABs) and changes in the lattice parameter of the γ′-phase around the LABs in the root of single-crystalline (SX) turbine blades made of CMSX-4 superalloy were studied. The blades with an axial orientation of the [001] type were solidified using an industrial Bridgman furnace with a 3 mm/min withdrawal rate. X-ray diffraction topography, the EFG Ω-scan X-ray diffraction method, scanning electron microscopy, and Laue diffraction were used to study the thin lamellar samples with a thickness of 0.5 mm and orientation of the surface perpendicular to the [001] direction. It is found that in the areas with a width of a few millimetres around LABs, decreases in the lattice parameter of the γ′-phase occur. These lattice parameter changes are related to the internal stresses of the γ′-phase caused by local changes in the concentration of alloying elements and/or to the dendrite bending near the LABs. X-ray topography used on two surfaces of thin lamellar samples coupled with the lattice parameter measurements of the γ′-phase near the LAB allows separating the misorientation component of LAB diffraction contrast from the component and visualising the internal stresses of the γ′-phase.

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.…”

“…However, some methods give information about the changes of the nanoscale structure for the points of the macroscopic areas. These include, for example, the positron annihilation spectroscopy (PAS) method [20,32] or the Mössbauer spectroscopy (MS) method [33], as well as X-ray diffraction methods [20,[34][35][36][37]. In the PAS and MS methods, data for each measuring point are collected from a sample area of several tens of mm 2 , while the X-ray diffraction methods allow for collecting data from the area above one mm 2 .…”

Effect of Blade Geometry on γ′ Lattice Parameter and Primary Orientation of SX Cored Turbine Blades (II)

“…For α(Z d1 ) in the scope limited by Z d1 ranged between 1 mm and 6 mm and between 8 mm and 12 mm, no clear correlations between α(Z d1 ) and a γ′ (Z d1 ) were observed despite changes of a γ′ equal to 0.002 Å, that is higher than the fluctuation range for the scope limited by Z d1 between 1 mm and 6 mm, and for Z d1 greater than 10 mm. It can be assumed that in these areas, measuring line d 1 passes through macroscopic low-angle boundaries (LAB), near which a γ′ changes significantly [ 34 ]. Such boundaries, which occurred in large numbers in similar-cored blades near the CB3, were shown in [ 35 ].…”

Lattice Rotation and Deformation Mechanisms under Tensile Loading in a Single-Crystal Superalloy with [001] Misorientation

“…The literature explains that lattice rotation and slip deformation are the primary mechanisms of deformation in single-crystal superalloys [ 24 , 30 ]. This study observes significant differences in lattice rotation and microstructural deformation organization among specimens with different deviation angles.…”

“…The [011] orientation requires significant rotation to facilitate cross-slip, resulting in considerable primary creep strain and the shortest creep life for crystals in this orientation. Subsequent studies on lattice rotation have emerged [ 24 , 25 , 26 ], primarily addressing the creep deformation of single-crystal superalloys under asymmetric loading. Asymmetric loading is characterized by a certain angular deviation of the specimen’s orientation from the [001] direction, leading to a misalignment between the crystallographic axes and the applied loading axes.…”