Irradiation damage of oxide dispersion strengthened steels

Advanced fission and fusion power offer long-term energy production from fundamentally carbon-free fuel sources, with high-energy densities and high reliability. However, for these power sources to be realised, many materials challenges need to be addressed. Oxide dispersion strengthened (ODS) ferritic alloys are recognized as potential fission fuel cladding and fusion structural materials because of their high-temperature stability and swelling-resistance imparted by the nano-scale oxide clusters they contain. This work presents the study of a set of model ODS alloys with a systematic variation in alloy chemistry in order to investigate the influence of chemical additions on the oxide cluster nature and the irradiation resistance. To investigate these properties, the high-resolution characterisation techniques of atom probe tomography and transmission electron microscopy were applied in combination with nanoindentation to assess mechanical properties and X-ray diffraction to study the crystallinity. The quantification of the character of the oxide particles in these ODS alloys by atom probe tomography presented a number of challenges and I extend the conventional analysis techniques in order to overcome these difficulties. By comparison of the addition of Ti, and then Cr, to a Fe-Y2O3 alloy, the influence of alloy chemistry on the oxide particles was evaluated. The main aims were to investigate the microstructure, the oxide cluster composition and to set a baseline to which the irradiated samples were compared. The irradiation damage of the oxide clusters was investigated using ion irradiation as an analogue for neutron damage. Irradiation experiments were performed at a range of temperatures and the stability of the clusters was assessed based on their size, number density and chemistry. Subtle changes in cluster chemistry at elevated temperatures and the dramatic changes which occurred after irradiation at low temperatures lead to conclusions about the competition of thermal diffusion and irradiation damage.