TEM in situ compression pillar testing of irradiated ODS alloys

TEM in situ micropillar compression tests are a promising approach for quantitatively determining mechanical properties of volume-limited materials, especially near-surface ion-irradiated damage layers.  We have demonstrated a reliable, repeatable method for machining micropillars from an irradiated bulk specimen, wherein the pillars are entirely contained within the shallow ion-irradiated layer.

Size effects become dominant in pillar geometries as small as those used for TEM in situ compression.  These size effects are generally attributed to an insufficient number of dislocation sources and obstacles to dislocation motion, within the specimen.  However, since we focus our study on oxide dispersion strengthened (ODS) alloys, which contain a high number density of finely dispersed oxide nanoparticles, we hypothesize the obstacle density is sufficient to overcome size effects.  We directly measure reasonable values of yield strength from TEM in situ compression pillars having minimum dimension > 100 nm.  This holds true in both the unirradiated and ion-irradiated specimens.

Measured elastic modulus values are approximately an order of magnitude lower than expected values.  But we couple the experimental observations with finite element modeling to adjust for deformation and deflection in the base of the compression pillars, resulting in reasonable moduli.

Collaborators:

  • Y.Q. Wu, Center for Advanced Energy Studies

Support:

  • US Nuclear Regulatory Commission award NRC-HQ-84-14-G-0056
  • DOE Nuclear Science User Facilities project 16-656

Products:

  1. K.H. Yano, M.J. Swenson, Y. Wu, and J.P. Wharry. TEM in situ micropillar compression tests of ion irradiated oxide dispersion strengthened alloy. Journal of Nuclear Materials 483 (2017) 107.  doi: 10.1016/j.jnucmat.2016.10.049
  2. K.H. Yano, M.J. Swenson, Y. Wu, and J.P. Wharry. Corrigendum to: “TEM in situ micropillar compression tests of ion irradiated oxide dispersion strengthened alloy”. Journal of Nuclear Materials 483 (2017) 107.  doi: 10.1016/j.jnucmat.2017.04.054
  3. K.H. Yano. In situ TEM micropillar compression testing in irradiated oxide dispersion strengthened alloys. M.S. Thesis, Boise State University, 2017.
  4. K.H. Yano, P.V. Patki, M.J. Swenson, and J.P. Wharry. Correlation between irradiation defects and transition dimension for TEM in situ mechanical testing. Transactions of the American Nuclear Society – 2017 Annual Meeting, 116 (2017) 22103.
  5. J.P. Wharry, K.H. Yano, M.J. Swenson, and Y.Q. Wu. In situ TEM mechanical testing: an emerging approach for characterization of polycrystalline, irradiated alloys. Microscopy & Microanalysis 22.S3 (2016) 1478.
  6. K.H. Yano, M.J. Swenson, and J.P. Wharry. In situ TEM microcompression pillar size effects in Fe-9Cr ODS. Transactions of the American Nuclear Society – 2016 Annual Meeting and Embedded Topical Meeting: Nuclear Fuels and Structural Materials, 114 (2016) 1048-1050.
  7. J.P. Wharry, K.H. Yano, M.J. Swenson, and Y.Q. Wu.  In situ TEM mechanical testing approaches for ion irradiated alloys.  International Conference on Plasticity, Puerto Vallarta, Mexico, January 2017.
  8. K.H. Yano and J.P. Wharry. TEM in situ cantilever testing to assess grain cohesion in irradiated ODS. Materials Science & Technology (MS&T) 2016, Salt Lake City UT, October 2016.
  9. J.P. Wharry, K.H. Yano, M.J. Swenson, and Y.Q. Wu.  TEM in situ mechanical testing techniques for ion irradiated materials.  13th International School on Degradation and Aging of Materials of Nuclear Power Units During Operation, Moscow Engineering Physics Institute, Moscow, Russia, October 2016.
  10. K.H. Yano, M.J. Swenson, and J.P. Wharry. TEM in situ micropillar compression testing of self-ion irradiated ODS alloys. European Materials Research Society, Warsaw, Poland, September 2016.
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