Research examines defect distribution at metal-oxide interface for future reactor material

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This inverse Fast Fourier Transform reconstruction, as uncovered by transmission electron microscopy, shows irradiation induced dislocations at the interface. The dislocations, not present in the unirradiated material, are behind a mechanism for the redistribution of radiation-induced point defects. The dislocations cause defect accumulation close to the interface.

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Materials under high energy radiation in a nuclear reactor develop various types of defects, including vacancies, interstitials, dislocations and voids. In such a hostile environment, a thin oxide layer formed on the metal protects the surface from corrosion. But it remains understudied and not fully understood how the presence of the oxide layer impacts the evolution of radiation defects in the metal. A new Journal of Applied Physics paper from a research team including Los Alamos National Laboratory scientists examines the defect distribution of an irradiated metal and oxide interface and how it evolves with an increasing dose of radiation. The research found surprising radiation-induced defect distribution mechanisms at the metal and oxide interface, and that radiation-induced dislocations at the interface preferentially absorb interstitials and affect defect distributions in the metal.

In an extreme environment that combines high temperature, high pressure and corrosive media, defects can gradually degrade materials. The research team used two types of characterization to discover the radiation-induced defect distribution mechanism at the metal-oxide interface: positron annihilation spectroscopy, which measures the elapsed time between the implantation of positrons into material and the emission of annihilation radiation, and transmission electron microscopy, which transmits electrons through a material for imaging. At the ion beam laboratories at Los Alamos National Laboratory and Sandia National Laboratories, the team irradiated an Fe₂O₃/Fe bilayer with 2 megaelectron volt Fe ions with an implantation depth of ~1 micrometer. The oxide was 50 nanometers thick.

At low doses of radiation, no significant vacancy accumulation was observed near the interface as the interface works as a neutral defect sink. However, with increasing doses, the formation of radiation induced dislocations at the interface suggested preferential absorption of interstitials. Vacancy accumulation was observed accordingly in the metal underneath in the positron annihilation spectroscopy data. The results also demonstrate that the passive oxide layers formed during corrosion impact the defect distribution in the metal underneath. The team’s findings emphasize that the synergistic impact of radiation and corrosion will differ from their individual impacts.

Funding and mission

This work was supported by the Department of Energy Office of Science, Basic Energy Sciences. The work supports the Global Security mission area and the Materials for the Future capability pillar.

Reference

“Interface effect of Fe and Fe₂O₃ on the distributions of ion induced defects,” Journal of Applied Physics, 132, 105901 (2022); DOI: 10.1063/5.0095013. Authors: H. Kim, M.R. Chancey, T. Chung, Y. Wang, J.K. Baldwin, B.K. Derby, N. Li (Los Alamos National Laboratory); I. Brackenbury, F.A. Selim (Bowling Green State University); M.O. Liedke, M. Butterling, E. Hirschmann, A. Wagner (Helmholtz-Zentrum Dresden-Rossendorf); K.H. Yano and D.J. Edwards (Pacific Northwest National Laboratory).

Technical contact: Hyosim Kim (MST-8)