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

Włodzimierz Bogdanowicz,Jan Sieniawski,Jacek Krawczyk,Robert Paszkowski

doi:10.3390/ma12244126

Włodzimierz Bogdanowicz, Jan Sieniawski + Show 2 more

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https://doi.org/10.3390/ma12244126

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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.

Highlights

The nickel-based superalloys are the most widely used materials for production of single-crystalline (SX) turbines components, which is applicable in aerospace and energy sectors
The shape of the LB section may be similar to the shape of the solidification front with the assumption that the primary dendrite arms always grow in the [001] direction, which is always perpendicular to the crystallization front
The crystal orientation of the primary dendrite arms in the selector extension area of the root determines the areas and directions of lateral growth of such secondary dendrite arms in root, which cause the creation of the low-angle boundary type defects

Summary

Introduction

The nickel-based superalloys are the most widely used materials for production of single-crystalline (SX) turbines components, which is applicable in aerospace and energy sectors. The combination of good mechanical properties (i.e., high mechanical strength and creep resistance) and corrosion resistance at high temperature (e.g., the operating temperature is about 1150 ◦ C for TMS238) make superalloys useful in the production of blades for high pressure turbines [1,2,3,4]. The required properties are met for the SX blades made of nickel-based CMSX-4 superalloy, in which the [001] crystallographic direction is parallel to the blade axis. The SX turbine blades are usually obtained in casting molds by dendritic directional crystallization using the Bridgman technique. The process leads to the obtainment of the SX blade casts, the structure and defects of which largely depend on the array and crystal orientation of the formed dendrites, and in turn affect the blades properties

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