Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Posit
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Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy JACEK KRAWCZYK, WŁODZIMIERZ BOGDANOWICZ, ANETA HANC-KUCZKOWSKA, ANNA TONDOS, and JAN SIENIAWSKI Single-crystalline superalloy CMSX-4 is studied in the as-cast state and after heat treatment, with material being taken from turbine blade castings. The effect of the heat treatment on the defect structure of the root area near the selector/root connection is emphasized. Multiscale analysis is performed to correlate results obtained by X-ray topography and positron annihilation lifetime spectroscopy (PALS). Electron microscopy observations were also carried out to characterize the inhomogeneity in dendritic structure. The X-ray topography was used to compare defects of the misorientation nature, occurring in as-cast and treated states. The type and concentration of defects before and after heat treatment in different root areas were determined using the PALS method, which enables voids, mono-vacancies, and dislocations to be taken into account. In this way, differences in the concentration of defects caused by heat treatment are rationalized. https://doi.org/10.1007/s11661-018-4704-2 The Author(s) 2018
I.
INTRODUCTION
THE single-crystalline, Ni-based superalloys are widely used for production of high-pressure and high-temperature turbine components in aerospace and energy industry sectors. Due to the extreme work conditions of blades, especially high mechanical and thermal stresses, the specific properties with low concentration of structural defects are needed.[1–3] Nowadays, the CMSX-4 single-crystalline superalloy is commonly used by industry; castings produced in this way are suitable candidates for defect characterization studies. Directional dendritic solidification by the Bridgman technique is widely used for production of single-crystalline blades made from superalloys. Production technology and the complex shape of blade castings produce dendritic arrays that allow for the possibility of many defects to be produced during solidification. The defects
JACEK KRAWCZYK, WŁODZIMIERZ BOGDANOWICZ, ANETA HANC-KUCZKOWSKA, and ANNA TONDOS are with the Institute of Materials Science, University of Silesia in Katowice, 41-500 Chorzow, Poland. Contact e-mail: [email protected] JAN SIENIAWSKI is with the Department of Materials Science, Rzeszo´w University of Technology, 35-959 Rzeszow, Poland. Manuscript submitted March 14, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
may be related to the inhomogeneity of the chemical composition, morphology and size of c¢ particles, and the inhomogeneity of crystal orientation. Therefore, blades are subjected to complex heat treatment after casting, among others, to eliminate the chemical heterogeneity caused by directional dendritic crystallization.[4] The heat treatment parameters are appropriately selected to create new c/c¢ array (reprecipitation[4]) with optimized properties, caused by more homogeneous morphology, s
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