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Title: Radiation behaviour of high-entropy alloys for fusion reactor environments
Author: Fernández Caballero, Antonio
ISNI:       0000 0004 8501 2755
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2019
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The world is hungry for energy with an estimated need of 20 TW-year at present. The demand of electrical power (approximately 1/4) could be supplied by the construction of a few 1,000 nuclear fusion power plants each providing 1 GW of clean electrical energy. After achieving the main challenge of producing and confining a deuterium-tritium plasma, the economic, safety, and environmental impact factors will have to be considered for the development of advanced reactor structural materials. These materials will have to withstand demanding heat and radiation flux environments during an estimated 30-40 years of device lifetime with doses of 200 dpa and temperatures of 1,000 C. Current fusion structural candidate materials such as bcc ferritic/martensitic, fcc austenitic stainless steels, or ODS steels have serious limitations after exposure to radiation and heat fields in terms of their induced brittleness at room temperatures, or fracture by creep at high temperatures. HEA (high entropy alloys) are a new type of complex metallic material that are fabricated on the basis that the alloy contains multiple principal elements. HEAs have come to attention after their intrinsic radiation resistance, and excellent mechanical properties both at low and intermediate temperatures. The chemical complexity is at present the source of many hypotheses about their properties, in particular their phase stability at temperature and irradiation resistance. In this thesis, a novel formulation of short-range order based on electronic structure methods is developed for predicting phase stability in bcc HEAs. This was used to predict the formation of a bcc phase, associated with a Cr-Cr-Cr-Cr tetrahedron cluster, in an fcc lattice. In experimental work, in contrast to previous studies, but in agreement with the modelling results, a bcc phase enriched in Cr was observed in the fcc HEA CrMnFeNi following a recrystallisation heat treatment. This phase was also present after irradiating with Ni ions up to 20 dpa at temperatures of 300 and 450 C, although no significant increase in volume fraction was measured, indicating that matrix stability was maintained. The mechanical properties after the ion irradiation were investigated by nanoindentation. There was a significant increase in hardness with irradiation dose. The associated changes in microstructure were examined by transmission electron microscopy.
Supervisor: Mummery, Paul ; Pickering, Edward Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: irradiation damage ; nuclear fusion ; transmission electron microscopy ; nanoindentation ; cluster expansion ; ab initio ; high-entropy alloys ; monte carlo