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Title: Materials for Fusion Reactors - The Brittle-Ductile Transition in Vanadium
Author: Joseph, T. D.
ISNI:       0000 0001 3593 1970
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2008
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This thesis describes experiments investigating the brittle-ductile transition in single and polycrystalline vanadium using four-point bend specimens. Pre-cracks were created in the beams by machining a notch into the tensile surface using EDM, which produced a network of sharp cracks in the base ofthe notch. Single crystal material was vacuum annealed at 1000°C and 400°C. The material annealed at 1000°C was had a low concentrations of dislocations and interstitial hydrogen. It produced a sharp BOT typical of dislocation free material, with an activation energy of 0.26 eV ± 0.07 eV. Material annealed at 400°C had a low concentration of interstitial hydrogen and a normal dislocation density and produced a soft transition, typical of metallic materials with active dislocations, with an activation energy of 0.22 eV ± 0.02 eV. Unannealed single crystal material had a high concentration of interstitial hydrogen and a normal dislocation density and produced a soft transition with an activation energy of 0.14 eV ± 0.04 eV. Its behaviour was thought to be dominated by the effects of interstitial hydrogen. Annealed polycrystalline vanadium was found to be ductile at temperatures of 77 K and above. Unannealed polycrystalline vanadium was ductile at 77 K and at high temperatures but exhibited a region of brittle failure between approximately 100 K and 300 K. A number of unusual phenomena were observed in this material and were attributed to competing effects of interstitial hydrogen. A number of attempts to measure the velocity of dislocations in vanadium were unsuccessful but direct imaging of the plastic zones of a number of samples using EBSD was used to investigate dislocation activity at different points in the transition curves.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available