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Research Papers: NDE

Synchrotron Radiation Study on Alloy 617 and Alloy 230 for VHTR Application

[+] Author and Article Information
Kun Mo

Department of Nuclear, Plasma, and
Radiological Engineering,
University of Illinois at Urbana-Champaign,
104 South Wright Street,
Urbana, IL 61801;
Reactor Engineering and Fuel
Management Research Center,
China Nuclear Power Technology
Research Institute,
47/F, Jiangsu Mansion,
Yitian Road, Futian District,
Shenzhen 518026, China

Hsiao-Ming Tung, James F. Stubbins

Department of Nuclear, Plasma, and
Radiological Engineering,
University of Illinois at Urbana-Champaign,
104 South Wright Street,
Urbana, IL 61801

Jonathon Almer

Advanced Photon Source,
Argonne National Laboratory,
Argonne, IL 60439

Meimei Li

Nuclear Engineering Division,
Argonne National Laboratory,
Argonne, IL 60439

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received December 3, 2011; final manuscript received February 20, 2012; published online March 18, 2013. Assoc. Editor: Tribikram Kundu.

J. Pressure Vessel Technol 135(2), 021502 (Mar 18, 2013) (8 pages) Paper No: PVT-11-1218; doi: 10.1115/1.4007041 History: Received December 03, 2011; Revised February 20, 2012

High-energy synchrotron radiation has proven to be a powerful technique for investigating fundamental deformation processes for various materials, particularly metals and alloys. In this study, high-energy synchrotron X-ray diffraction (XRD) was used to evaluate Alloy 617 and Alloy 230, both of which are top candidate structural materials for the very-high-temperature reactor (VHTR). Uniaxial tensile experiments using in-situ high-energy X-ray exposure showed the substantial advantages of this synchrotron technique. First, the small volume fractions of carbides, e.g., ∼6% of M6C in Alloy 230, which are difficult to observe using laboratory-based X-ray machines or neutron scattering facilities, were successfully examined using high-energy X-ray diffraction. Second, the loading processes of the austenitic matrix and carbides were separately studied by analyzing their respective lattice strain evolutions. In the present study, the focus was placed on Alloy 230. Although the Bragg reflections from the γ matrix behave differently, the lattice strain measured from these reflections responds linearly to external applied stress. In contrast, the lattice strain evolution for carbides is more complicated. During the transition from the elastic to the plastic regime, carbide particles experience a dramatic loading process, and their internal stress rapidly reaches the maximum value that can be withstood. The internal stress for the particles then decreases slowly with increasing applied stress. This indicates a continued particle fracture process during plastic deformations of the γ matrix. The study showed that high-energy synchrotron X-ray radiation, as a nondestructive technique for in-situ measurement, can be applied to ongoing material research for nuclear applications.

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References

Figures

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Fig. 1

Microstructure of (a) Alloy 617 and (b) Alloy 230

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Fig. 2

Schematic of the X-ray diffraction experiment setup

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Fig. 3

Diffraction patterns from Alloy 230: (a) before and (b) after deformation

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Fig. 4

Representative X-ray diffraction pattern (quarter of an image plate) for Alloy 230. All Debye rings are identified as belonging to γ matrix and M6C carbides

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Fig. 5

Schematic of axial-scanning measurements

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Fig. 6

Lattice strain development for the γ matrix of Alloy 617 during tensile testing: (a) axial direction, ɛ11 and (b) transversal direction, ɛ22

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Fig. 7

Lattice strain development for the γ matrix of Alloy 230 during tensile testing: (a) axial direction, ɛ11 and (b) transversal direction, ɛ22

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Fig. 8

Orientation dependence of Young's modulus (unit: GPa) for Ni polycrystalline using Kröner's model: (a) 3D E(hkl) mapping (b) Calculated E(hkl) with comparison to the Voigt and Reuss limits

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Fig. 9

Result of internal stress in comparison to the true stress developed during the tensile test of Alloy 230: (a) (200), (b) (311), (c) (220), and (d) (222) reflections

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Fig. 10

Applied stress versus lattice strain for the γ matrix ((311) reflection) and the M6C carbide ((422) reflection) in Alloy 230. Note: The solid and dash lines are curves fitted though the data points to show the trend.

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