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Metals 2018, 8(6), 376; https://doi.org/10.3390/met8060376

Investigations into the Surface Strain/Stress State in a Single-Crystal Superalloy via XRD Characterization

1
School of Materials Science and Engineering, Beihang University, Beijing 100191, China
2
ICMMO/SP2M, University Paris-Sud, bat. 410, 91405 Orsay, France
*
Authors to whom correspondence should be addressed.
Received: 21 April 2018 / Revised: 19 May 2018 / Accepted: 21 May 2018 / Published: 23 May 2018
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Abstract

The present study was aimed at determining the surface strain/stress state in an Ni-based single-crystal (SC) superalloy that was subjected to two different cooling rates from solid solution temperature through using the X-ray diffraction (XRD) method. The normal stresses σ 11 s and σ 22 s were determined, then the Von Mises stresses ( σ V M s ) were derived from them. Field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscope (TEM) micrographs were taken to illustrate the strain/stress state change. The precipitation of the secondary γ′ phases in the γ phase and the formation of the dislocation in the interphase upon a slower cooling rate caused the γ phase lattice distortion to increase, so a larger σ V M s of the γ phase was realized in comparison to the faster cooling sample. For both of the two cooling modes, we found that the σ V M s of the γ′ phase increased due to the growth of the γ′ phase during the aging process. Also, the aging process led to pronouncedly anisotropic lattice mismatches in the {331} and {004} planes. In addition, the surface strain/stress states of a cylinder sample and a tetragonal sample were also studied using a faster cooling rate, and σ 11 s and σ 22 s were analyzed to explain the influence of the shape factor on the stress anisotropy in the [001] and [ 1 1 ¯ 0 ] orientations. The strain in the [001] orientation of the γ phase is more sensitive to the shape change. View Full-Text
Keywords: Ni-based single-crystal superalloy; XRD; surface strain/stress state; solid solution cooling speed; lattice distortion Ni-based single-crystal superalloy; XRD; surface strain/stress state; solid solution cooling speed; lattice distortion
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Duan, H.; Qin, L.; Pei, Y.; Li, S.; Zhao, L.-D.; Ji, V.; Gong, S. Investigations into the Surface Strain/Stress State in a Single-Crystal Superalloy via XRD Characterization. Metals 2018, 8, 376.

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