Investigaion of Grain Growth in Nanocrystalline Oxide Thin Films during Iradiation and Heating using In-Situ Tem

Grain growth, which occurs at elevated temperatures and under irradiation is manifests by an increase in the average grain size, a decrease in the number of grains, and a decrease in grain boundary total area. Nanocrystalline metals having very small sizes and high GB densities are of interest to the nuclear materials community not only for their improved mechanical properties but also for their radiation resistance, since grain boundaries are effective sinks for radiation-induced defects, ultimately impacting the radiation tolerance of nanocrystalline materials against net defect accumulation. However, even if nanocrystalline metals present increased radiation tolerance at the nanoscale, irradiation-induced grain growth is responsible for grain enlargement and annihilation of these benefits. While the literature shows several studies on this particular topic of grain growth in nanocrystalline metals, very little focus was put on grain growth in nanocrystalline oxides, especially under irradiation. The scarce available literature focuses on fuel oxides. In this work, grain growth kinetics was studied in Fe₂O₃, Fe₃O₄, Cr₂O₃ which are oxides commonly forming on components in nuclear reactor such as the ones made of steel. Thin films with nanocrystalline grain size were grown by Pulse Laser Deposition or Sputtering Deposition and subject to thermal annealing <i>in situ</i> in a Transmission Electron Microscope to follow the grain-growth. Samples were also irradiated <i>in situ</i> in the TEM at temperatures from 50 K to 773 K using 1 MeV Kr²⁺ ions to 10 dpa to study grain-growth under irradiation. Grain size was measured as a function of time for the thermal grain growth and in terms of irradiation dose (i.e. dpa) for the irradiated samples. The kinetics of grain growth was then discussed in the light of the literature and how it compares to the thermal spike model developed for metals.