The joining development, metallurgical study and characterisation approach of brazed joints between tungsten and fusion related materials for divertor applications

Student thesis: Doctoral Thesis

Abstract

The design of brazed joints between tungsten to other fusion related materials is a significant challenge in developing fusion reactors, largely due to the dissimilar physical metallurgy of the materials to be joined. Under extreme thermal loading and plasma irradiation conditions, selecting suitable materials is very restricted and poses a significant challenge to the design. The candidate brazing filler materials for fusion related materials are often unconventional and lack material data and design experience. The work presented in this thesis focuses on the design and fabrication of dissimilar brazed joints between tungsten and fusion relevant materials with novel gold-based fillers. Vacuum furnace brazed joints of tungsten-tungsten, tungsten-Eurofer 97, tungsten - copper and tungsten-SS316L are successfully joined with a novel gold-based Au80Cu19Fe filler. Metallurgical and interfacial studies have been carried out for each brazed joint to understand their microstructural properties, and nanoindentation testing was performed at the joints to generate mechanical properties of the brazed layers. Optimised brazing procedures for vacuum furnace brazing and induction brazing were developed to limit the defects within the brazed layers with an equivalent Au80Cu20 filler. The brazing developments showed that the gold-based fillers could be used to fabricate qualified brazed joint between tungsten and the dissimilar materials considered. The brazing process design has been used for the proof-of-concept study of divertor mock-up fabrications, and the findings have contributed to the limited test data on fusion relevant materials. Finally, due to the substantial procurement costs of the gold-based filler material and the inability to generate macro scale properties from the braze layer, the use of conventional Cu60Zn40 fillers allowed a casting and brazing process methodology to be developed to correlate the in situ mechanical properties within the brazed layer to the properties generated by macro-level mechanical testing. The findings showed that this methodology could be used for predicting the mechanical properties of the brazed layer by the cast and heat-treated macro-level filler metal specimens, which are applicable to brazed joints in a range of applications.
Date of Award10 Jun 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorAlexander Galloway (Supervisor) & James Wood (Supervisor)

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