Variation of Crystal Orientation and Dendrite Array Generated in the Root of SX Turbine Blades

Abstract

The variation of the crystal orientation and the dendrite array generated in the root of the single-crystalline (SX) turbine blades made of CMSX-4 superalloy were studied. The blades with an axial orientation of the [001] type were solidified by the industrial Bridgman technique using a spiral selector at a withdrawal rate of 3 mm/min. The analysis of the crystal orientation and dendrite arrangement was carried out using scanning electron microscopy, X-ray diffraction topography, and Laue diffraction. It was found that the lateral growth of such secondary dendrite arms, which are defined as “leading” and grow in the root at first, is related to the rotation of their crystal lattice, which is the reason for creation of the low-angle boundary (LAB) type defects. The primary crystal orientation of the selector extension (SE) area determines the areas and directions of the lateral growth of the leading arms. Additionally, it was found that in the SE areas of the root, near the connection with the selector, the spatial distribution of the [001]γ′ crystallographic direction has a complex wave-like character and may be related to the shape of the crystallization front.

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

“…The misorientation of the neighboring areas of the dendrite array, described as a local heterogeneity of crystal orientation, can lead to the formation of low-angle boundaries (LABs) that reduce creep resistance and other strength parameters. The reduction can take place in two ways: globally, by the deviation of the mean crystal orientation from the [001] direction, and locally, by local crystal orientation changes causing the formation of LABs [ 13 , 14 , 15 ]. The dislocation of LABs can cause the strong segregation of the Re alloy additive during high-temperature service [ 16 ] as well as the loss of “the solid-solution strengthening effect of Re atoms” [ 16 ].…”

Heterogeneity of the Dendrite Array Created in the Root of Cored SX Turbine Blades during Initial Stage of Crystallization

“…As stated in Ref. [ 11 , 24 ], each of the dendrite chains of a 1 –a 3 type, visible on the P surface, is the result of the growth of a set of tertiary dendrites in the Z direction from the laterally growing single secondary arm below the P surface which was named as the leading arm. In the SE subarea the dendrites grow directly from the selector (three double arrows, Figure 1 c), that is why the chains occur less often.…”

“…In Ref. [ 11 , 24 ], it was stated that each group of the dendrites of UGA type subarea is created by the tertiary dendrites that grow almost parallel to the Z axis from a single secondary dendrite growing laterally near the bottom surface of the root.…”

“…The undisturbed growth of the dendrites with the cubic FCC structure takes place in the direction of [001], which is parallel to the withdrawal direction in the Bridgman method. However, the directional crystallization in a mould with a complex shape can lead to heterogeneity of the dendrite array and its crystal orientation [ 10 , 11 , 12 ]. This significantly affects the quality of the blade [ 1 , 13 , 14 ].…”

Design, growth, and characterization of Y2Mo4O15 crystals for Raman laser applications

“…To facilitate a precise investigation of the crystallinity of an asgrown crystal, the Laue back-reection measurement is broadly exploited. 34 The characteristic Laue back-reection patterns of different positions in the (100) crystal wafer are accordant and distinct, as shown in Fig. 4.…”