This investigation aims at probing the radiation induced defects in Nickel/Oxide systems. The mobility and transport of defects by in-situ transmission electron microscopy allows to follow the micro-stuctural evolution of the irradiation induced defects in real time for experiments conducted at a wide range of temperatures. In addition to high temperatures, the investigation of the oxide at cryogenic temperatures allows the study of the amorphization behavior of the oxide.

In this proposed work, cross-sectional TEM specimens of Ni/NiO and (Ni-18%Cr)/NiO multilayers prepared by FIB lift-out technique will be irradiated in-situ in the microscope at the IVEM of ANL at temperatures from 20 to 773K using 1 MeV Kr2+ ions to 10 dpa similar to previous Fe-based samples irradiation conditions. The large range of temperatures is meant to provide information on the range of mobility of irradiation induced defects as a function of temperature. In addition, the cryogenic temperature will allow the study of the amorphization behavior of the oxide.

The microstructure evolution under irradiation will thus be followed and characterized at successive doses, using bright field and (g, 3g) weak beam dark field TEM imaging methods. Diffraction patterns will also be acquired at each irradiation condition. Furthermore, videos will be recorded throughout irradiation for subsequent frame-by-frame analysis (15 frames/s). The study of the mobility of the defects focuses on the identification of dislocation loop Burgers vectors, nature (interstitial vs. vacancy) and density as a function of dose. Special attention will be put on the characterization of the type of defect (faulted vs unfaulted loops and Burgers vector). Due to the time-consuming nature of this involved technique requiring the imaging of the same loops under several different diffraction conditions, this analysis will be conducted ex-situ at NCSU after the experiments are complete. In relation to the amorphization of the oxide, the formation of amorphous rings in the diffraction patterns as well as the loss of diffraction contrast in the bright field images will be investigated.

The ex-situ microchemistry analysis will be carried out at the NCSU using ChemiSTEM to evidence diffusion behavior under irradiation. Elemental mapping using the ChemiSTEM method will be carried out at interfaces of metal/oxide multilayers. In addition to the ex-situ ChemiSTEM mapping, high resolution TEM and high resolution STEM electron energy loss spectroscopy (EELS) will be utilized to characterize the valence state of Nickel and Chromium before and after irradiation at the interface between the metal and the metal oxide. Capturing any change in the valence state at the interface between the metal and the metal oxide will provide evidence of any oxygen diffusion across the interface due to an influx of point defects to this feature.

The Office of Basic Energy Sciences in the U.S. Department of Energy established the Energy Frontier Research Center (EFRC) program since 2009, to accelerate scientific breakthroughs that are needed to strengthen the United States’ economic leadership and energy security. Each EFRC are funded for four years between $2M and $4M annually. In June 2018, a proposal to better understand the links between radiation damage and corrosion in nuclear energy systems has received the green light to become a new EFRC. The full name of this new EFRC is Fundamental Understanding of Transport Under Reactor Extremes, or FUTURE. It is led by the Los Alamos National Laboratory (LANL) under Dr. Blas Uberuaga’s direction, and our group at the North Carolina State University (NCSU) is part of the winning team.

Instead of looking at the effects of just one variable, FUTURE will explore the coupling of radiation damage and corrosion in order to predict irradiation-assisted corrosion in passivating and non-passivating environments for materials in nuclear energy systems. Variables to be studied include temperature, radiation exposure, corrosion, stress and time. Mechanistic modelling is fully part of this effort, in close collaboration with the experimentalists.

The knowledge will ultimately improve the performance and predictability of materials used in advanced nuclear systems. FUTURE’s research supports the United States’ energy security mission area and its Materials for the Future science pillar through the creation of design principles, synthesis pathways, and manufacturing processes for materials with predictable performance and controlled functionality.