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Title: On nanosized precipitates in steels for advanced nuclear reactors
Author: Davis, Thomas Paul
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2020
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Nuclear fission power is a reliable and zero carbon-dioxide emitting energy source and nuclear fusion is regarded as the ultimate terrestrial energy source. Both processes require radiation resistant structural reactor core materials. Atom probe tomography, nanoindentation, and electron microscopy were used to investigate a) radiation-induced precipitation of nanosized Mn-Ni-Si precipitates (MNSP) and nanosized copper-rich precipitates (CRP), and radiation-induced solute segregation to dislocations in neutron and ion irradiated T91 ferritic-martensitic steel and b) the effect of yttrium-titanium-oxygen (Y-Ti-O) nanosize precipitates on the grain structure and mechanical properties of Fe-14Cr-W-0.25Ti-0.25Y2O3 (14YWT (wt%)) oxide dispersion strengthened steel. Two neutron irradiated T91 steel conditions were investigated: 2.14 dpa at 327C and 8.82 dpa at 377C. The MNSP compositions fell near the MnSi(Ni) phase field, which is distinctly different than the typically cited 'G-phase' (Mn6Ni16Si7). MNSPs appeared as a co-precipitated appendage to CRPs. CRP-MNSP number densities, radii, and volume fractions agreed well with literature cluster dynamics model. Parallels were drawn between the limited database on MNSPs in neutron irradiated Fe-Cr alloy systems with the extensive literature on precipitate evolution in reactor pressure vessel steels. T91 was Fe4+ irradiated from 0.12 dpa to 4.1 dpa at ∼300°C with the characterisation of MNSP and their impact on mechanical properties were discussed. 14YWT Y-Ti-O (7-15 nm diameter; number density 1023 − 1024 #/m3) particles had a small effect on the hardness, suggesting that the dominant hardening mechanism was related to the grain boundary refinement rather than the dislocation pinning on the oxides.
Supervisor: Armstrong, D. E. J. ; Moody, M. P. ; Bagot, P. A. J. ; Auger, M. A. Sponsor: Clarendon Scholarship
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Science