This study concerns four high performance structural alloys designed to withstand the extreme temperature and irradiation environment inside fusion and fission fast breeder reactors: two Reduced Activation Ferritic Martensitic (RAFM) steels (Fe-14wt%Cr and a European standard alloy EUROFER97) and two equivalent Oxide Dispersion Strengthened (ODS) steels (Fe-14wt%Cr ODS (CEA ODS) and EUROFER ODS). Neutron irradiation of the samples was impractical due to timescale and specific handling requirements for radioactive samples. Instead, ion implantation was used to simulate the helium and damage of neutron irradiation. Samples of each alloy were subjected to a range of ion implantations: 75appm He, 2000appm He, 2000appm He + 4.5dpa Fe and 2000appm Ne. The matrix of four materials and five implantation conditions was analysed using the following experimental techniques: nanohardness indentation, Vickers hardness testing, micropillar compression, microcantilever bending, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). These techniques were used to compare the properties of the unimplanted materials and their response to implantation. Yield stress (σ<sub>y</sub>) was comparable across hardness testing and microcantilever bending, and consistently showed σ<sub>y</sub> Fe-14wt%Cr < EUROFER < EUROFER ODS < CEA ODS. When subject to helium implantation, 75appm He caused insignificant changes in σy while 2000appm He increased σ<sub>y</sub> in all materials. This increase was most significant in Fe-14wt%Cr due to its low grain boundary density and lack of oxide/carbide particles. The particle dispersions in the other materials act as helium traps, preventing the formation of TEM visible bubbles and reducing the hardening effects of the helium. Across all results it becomes clear that, although not to the degree of the ODS materials, EUROFER is more radiation resistant than Fe-14wt%Cr. It therefore appears that it is the presence of a complex microstructure including small grains and a distribution of oxide or carbide particles, rather than the specific inclusion of oxide nanoparticles, that provides RAFM steels with superior irradiation resistance properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:711958 |
| Date | January 2015 |
| Creators | Grieveson, Eleanor M. |
| Contributors | Roberts, Steve |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:6234be04-02f3-44bd-9b11-cc915b2ecbee |
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