Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Jacek Krawczyk,Aneta Hanc-Kuczkowska,Anna Tondos,Jan Sieniawski,Włodzimierz Bogdanowicz

doi:10.1007/s11661-018-4704-2

Abstract

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.

Highlights

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
The mutual arrangement of short-range and long-range arms allows visualization of a ring that overlaps the edge of the PSC area and is marked by RC (Figure 3(b))
No clear dendritic structure was observed on the metallographic sections of the ST surface of T-type parts

Summary

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.[1,2,3] 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.

Results

Discussion

Conclusion