Thesis
Investigating the static corrosion of T91 for lead-bismuth eutectic reactors at the atomic scale
- Abstract:
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T91 steel is a candidate material for structural components in lead-bismuth-eutectic (LBE) cooled systems, for example, fast reactors and solar power plants. However, the corrosion mechanisms of T91 in LBE remain poorly understood. In this study, we have analysed the static corrosion of T91 in liquid LBE using a range of characterisation techniques at increasingly smaller scales. Both the corrosion in reducing and oxidising environments are considered. Several different corrosion mechanisms are identified and the effect of oxygen content on LBE corrosion is investigated.
Oxygen concentration strongly influences the corrosion pattern. In a reducing environment (low oxygen content), the physical dissolution of elements (e.g. Fe, Cr) in LBE is the main factor with slight oxidation happening at the interface of T91 and LBE. A unique pattern of liquid metal intrusion is observed that does not appear to correlate with the grain boundary network. Atomic scale elemental redistribution and 3D morphology of the corrosion interface are revealed using scanning transmission electron microscope (STEM) and atom probe tomography (APT). A thin surface oxide layer (presumably wüstite) is observed at the LBE-steel interface.
In an oxidising environment (high oxygen content), preferential oxidation at grain boundaries is the dominant process, with LBE penetration into materials happening more locally. Complex oxide structures are identified with the use of STEM and APT. Moreover, the quality of the oxide layer may directly influence the protection effect.
Upon closer inspection, electron backscatter diffraction (EBSD) reveals a change in the morphology of grains at the LBE-exposed surface for both reducing and oxidising environments, suggesting a local phase transition. Energy dispersive X-ray (EDX) maps show that Cr is depleted in the T91 material near the LBE interface. The dissociation of Cr carbides and the overall Cr depletion adjacent to the corrosion interface show a potential correlation to the phase change observed in this region. High-resolution electron backscatter diffraction (HR-EBSD) and micro-beam Laue X-ray diffraction measurements further support the results. Based on this detailed nano-scale information from STEM and APT, a potential mechanism of Cr depletion, Cr carbide dissociation, and phase change in T91 induced by LBE corrosion is proposed.
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(Preview, Dissemination version, pdf, 18.5MB, Terms of use)
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Authors
Contributors
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Materials
- Role:
- Contributor
- Institution:
- University of Oxford
- Role:
- Contributor
- Role:
- Contributor
- Role:
- Contributor
- Role:
- Contributor
- Funder identifier:
- https://ror.org/0439y7842
- Funding agency for:
- Moody, M
- Grant:
- EP/T011505/1
- Programme:
- An Atomic-Scale Characterisation Facility for Active Nuclear Materials.
- Funder identifier:
- https://ror.org/01bj3aw27
- Funding agency for:
- Short, M
- Grant:
- NEUP 19-16754
- Programme:
- Simultaneous Corrosion/Irradiation Testing in Lead and Lead-Bismuth Eutectic: The Radiation Decelerated Corrosion Hypothesis.
- Funder identifier:
- https://ror.org/0439y7842
- Funding agency for:
- Hofmann, F
- Grant:
- EP/T002808/1
- Programme:
- Simultaneous Corrosion/Irradiation Testing in Lead and Lead-Bismuth Eutectic: The Radiation Decelerated Corrosion Hypothesis (RC-3).
- DOI:
- Type of award:
- DPhil
- Level of award:
- Doctoral
- Awarding institution:
- University of Oxford
- Language:
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English
- Subjects:
- Deposit date:
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2025-04-10
- ARK identifier:
Terms of use
- Copyright holder:
- Minyi Zhang
- Copyright date:
- 2024
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