High temperatures, as well as high fluxes of neutrons and other highly energetic particles during the operation of a magnetic confinement plasma device (Tokamak) make imperative the use of materials that are resistant to high temperatures and radiation. Tungsten is a candidate plasma facing material for the interior walls of a fusion reactor due to its high melting point, high thermal conductivity, low tritium retention and heat stress resistance. However, tungsten suffers from brittle behavior at low temperatures due to the relatively high ductile to brittle transition temperature, limiting its exploitation.
The objective of Dimitris Papadakis’ PhD is the study of the annealing effects of fission neutron irradiated tungsten materials.
Selected neutron irradiated tungsten materials will be annealed in the temperature range of 600 – 1500 C with the aim of studying the restoration of the properties of tungsten to the pre-irradiated state. Neutron irradiation causes damage in a material, resulting in the creation of defects. With the use of Positron Annihilation Lifetime Spectroscopy the type and percentage of open volume defects will be determined. Additionally, optical and electron microscopy (SEM), as well as X-ray diffraction (XRD) will be used to determine the changes in the structure of the materials during annealing and irradiation.
Annealing at very high temperatures results in structural changes of the tungsten material through diffusion and the interaction of various defects in the crystalline lattice, or even through the mechanism of recrystallization. These structural changes lead into the change of the mechanical and electrical properties of the materials. Through various techniques of characterization of mechanical properties (Macro-Nano Indentation, Impulse Excitation) and electrical properties (DC Resistivity), structural changes will be correlated with changes in the physical properties of the material.
The PhD thesis will be defended at the Physics Department of UoA.