Congratulations to Matthew Lloyd, an Oxford Fusion CDT student who successfully defended his thesis at viva earlier this year. Matthew’s thesis is entitled “Radiation Damage and Transmutation in Tungsten-Alloys for Nuclear Fusion Applications” and supervisors are David Armstrong (Oxford), Michael Moody (Oxford), Paul Bagot (Oxford); Duc Nguyen-Manh (UKAEA) and Enrique Martinez (Los Alamos National Laboratory).
Matthew will be moving to Singapore once travel restrictions are eased, to start a postdoctoral position working on the development of radiation damage tolerant materials.
An abstract from Matthew’s thesis is below.
“In this work, the effect of neutron-induced radiation damage and transmutation on the microstructure of W is investigated. Samples irradiated in the High Flux Reactor to a dose of 1.67 dpa at 1173 K were characterised using a combination of atom probe tomography and electron microscopy based techniques. Characterisation showed a microstructure dominated by voids and precipitates rich in Re and Os atoms produced via transmutation. Voids were shown to be decorated with Re and Os. Samples with equivalent Re and Os concentrations were produced via arc melting by ACI alloys, and heavy-ion irradiated at Sandia National Laboratory, USA, to a peak dose of 1.7 dpa at 1173 K. Characterisation using APT and TEM was used to highlight key differences in the microstructure produced by ion and neutron irradiation, including a smaller average void size and weaker precipitate formation. The clusters observed under ion irradiation were smaller, more diffuse and consisted primarily of Os, with slight enrichment of Re measured using cluster analysis techniques. The clusters in the neutron irradiated material on the other hand were dense and comprised mainly of Re, but with a central Os rich core. Cluster analysis methods showed cluster compositions comparable to samples from the Joyo reactor, however, line profile analysis suggested that some of the clusters had a composition consistent with σ phase in the centre. Kinetic Monte Carlo simulations of W-Re showed that transport of Re to point defect sinks occurred via mixed interstitial defects. A new energy model including Os was developed in which more accurate vacancy interactions were modelled by introducing local vacancy concentration dependant interactions. Analysis of the binding energies showed that Re and Os bind strongly to vacancies, and that Os had the strongest binding. The new model was used to simulate the formation of voids in W under irradiation and forms the basis for further study of the phenomena observed experimentally in this thesis.”