In Situ Thermomechanical Property Monitoring During Ion Beam Irradiation

Cody Dennett, Massachusetts Institute of Technology

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Currently, few methods exist for characterizing irradiated material performance in situ, during exposure. Techniques such as in situ TEM or in situ Raman spectroscopy can provide local structural information during irradiation, but no current methods can continuously monitor bulk thermal and mechanical properties. The ability to observe changes in thermomechanical properties in real time would allow for high-resolution mapping of dose-property relationships at a fidelity not previously possible. In addition, such a tool could be used for detecting emergent irradiation-induced microstructural evolution such as the transition from incubation to steady-state void swelling. Transient grating spectroscopy (TGS) is a non-contact, non-destructive methodology suited for this purpose. By optically inducing and monitoring monochromatic surface acoustic waves (SAWs), the thermal diffusivity and elastic properties of materials may be determined. A time-resolved implementation of this technique has been developed with sufficient sensitivity to continuously monitor microstructural evolution during irradiation. As proof-of-concept experiments, ion irradiation-induced property changes have been measured post-irradiation on pure, single-crystal copper. TGS measurements indicate the presence of volumetric void swelling, which is confirmed with scanning transmission electron microscopy (STEM). An in situ TGS beamline experiment for concurrent ion beam irradiation and property monitoring is in use on a 6 MV tandem accelerator at the Sandia Ion Beam Laboratory. This facility can monitor material evolution at high temperatures in real time under ion bombardment. Using high-energy self-ions, radiation damage effects on the thermomechanical properties of pure metals are being studied. These experiments and methods will be used as a screening tool to expedite the design and testing process for advanced nuclear materials. Such tools will not only allow for dose-property relationships to be studied in much greater detail than previously possible but also provide rapid, engineering-relevant data capable of speeding the innovation cycle in nuclear material development.

Abstract Author(s): Cody A. Dennett, Khalid Hattar, Michael P. Short