Date: Thursday, Oct 1st
Presenter: Dr. Janelle Wharry, Boise State University
Oxide dispersion strengthened (ODS) alloys are leading candidates for cladding and structural components in advanced fission nuclear reactors. ODS alloys contain a fine dispersion of Y2Ti2O3 nanoparticles in an Fe-Cr matrix, which enhance the radiation resistance and high-temperature strength of the alloy. But in service, ODS components will be subject to extreme operating conditions of up to 500 displacements per atom (dpa) at up to 700°C, which will alter the designed microstructure and mechanical properties of the material. In particular, the oxide nanoparticles exhibit limited stability under irradiation. As such, the hardening mechanisms of the alloy will change as the nanoparticles evolve. The objective of this talk is to understand the evolution in hardening mechanisms of an Fe-9Cr ODS alloy under irradiation, especially as it relates to the microstructural evolution of the alloy.
In this study, a model Fe-9Cr ODS alloy was irradiated to two conditions: with neutrons to 3 dpa at 500°C, and with 5 MeV Fe++ ions to 100 dpa at 400°C. Specimens were examined using a combination of transmission electron microscopy (TEM) and local electrode atom probe (LEAP) tomography to characterize the irradiated microstructure. Irradiation hardening was measured by nanoindentation. The Orowan dispersed barrier hardening model was used to calculate hardening from microstructure observations, but it significantly underestimated hardening measured by nanoindentation. This disparity was attributed to oxide nanoparticle instability under irradiation. However, when the nanoparticle instability was considered in a solid solution strengthening model, measured and calculated hardness fell into close agreement.
Dr. Janelle Wharry is an assistant professor in the Department of Materials Science and Engineering at Boise State University. She received her Ph.D. from the University of Michigan in 2012. She continued working as a post-doctoral research fellow at Michigan until joining the faculty at Boise State in January 2013. Dr. Wharry has extensive experience studying the effects of irradiation on materials using a range of microscopy techniques, multiscale mechanical testing techniques, and computational models. She has expertise on charged particle irradiation experiments, materials characterization, and transmission electron microscopy in situ mechanical testing. In her early career, she has delivered over 30 conference presentations and over 15 invited talks. Dr. Wharry is an affiliate faculty of the Center for Advanced Energy Studies, and has previously held positions at Duke Energy, Westinghouse, and Sandia National Laboratories.