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In Situ SEM Push-to-Pull Micro-tensile Testing of Ex-service Inconel X-750

  • C. HowardEmail author
  • C. D. Judge
  • H. T. Vo
  • M. Griffiths
  • P. Hosemann
Conference paper
Part of the The Minerals, Metals & Materials Series book series (MMMS)

Abstract

A novel lift-out, push-to-pull, micro-tensile, small scale mechanical testing (SSMT) technique was developed to assess the yield strength, failure strength, and failure mechanisms of activated ex-service Inconel X-750 removed from the CANDU nuclear reactor core after extended service. Neutron irradiated Inconel X-750 components fail in an intergranular manner. Because these ex-service components are less than 1 mm in thickness, conventional tensile specimens cannot be fabricated from them. Thus, large-scale testing is not possible, and specimens on the order of 1 μm × 1 μm × 2.5 μm (thickness × width × gauge length) containing individual boundaries were fabricated in order to assess the grain boundary strength of the material as a function of irradiation temperature and dose. The variability introduced by differences in thermo-mechanical processing during fabrication was also assessed. Application of this new micro-tensile testing technique to non-irradiated Inconel X-750 gives good agreement with the bulk yield strength of the nickel superalloy, 1070 MPa. From SSMTs, the measured yield strengths of non-irradiated specimens were 1001 MPa at the outer edge and 1043 MPa at the center of the component. Cold work, introduced by grinding of the outside surface of the component, reduces ductility, as does irradiation. Initial tests indicate that away from the surface in the center, the boundary strength was reduced by ~456 MPa after irradiation to 78 dpa at an average irradiation temperature of 180 °C; the corresponding ductility decreased from 16.6 to ≤2.3% total elongation. Testing is a work in progress and more tests are needed for higher precision with regards to grain boundary strength reduction.

Keywords

Small scale mechanical testing Grain boundary strength Micro-tensile Micromechanics 

Notes

Acknowledgements

The authors of this manuscript would like to acknowledge Canadian Nuclear Laboratories and the CANDU Owners Group (COG) for their donation of sample material and the Nuclear Science User Facility (NSUF) sample library at Idaho National Lab (INL) operated through the U.S. Department of Energy (DOE), Nuclear Energy University Program (NEUP), Rapid Turnaround Post-Irradiation Experiment (RT-PIE) for instrument time, sample management and preparation. Grant Bickel and Don Metzger are acknowledged for useful discussion, and Marc Paulseth for temperature estimates. The authors would like to thank COG for financial support for some of this work and permission to use the data. In addition, the authors would like to thank the Biomolecular Nanotechnology Center (BNC) at the University of California, Berkeley (UCB) for the use of the FEI Quanta 3D FEG. We would also like to recognize INL microscopist James W. Madden for sample preparation and Leandro Von Werra at the University of Bern for use of his digital image correlation software.

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Copyright information

© The Minerals, Metals & Materials Society 2019

Authors and Affiliations

  • C. Howard
    • 1
    Email author
  • C. D. Judge
    • 2
  • H. T. Vo
    • 1
  • M. Griffiths
    • 3
  • P. Hosemann
    • 1
  1. 1.Department of Nuclear EngineeringUniversity of California BerkeleyBerkeleyUSA
  2. 2.Canadian Nuclear LaboratoriesRadiation Damage and Deformation BranchChalk RiverCanada
  3. 3.Department of Mechanical and Materials EngineeringQueen’s UniversityKingstonCanada

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