Multiscale high-temperature mechanical performance of materials for nuclear fusion

Nuclear fusion is now being seriously considered as future power source for post 2050, as demonstrated by the recent announcement of the STEP construction in Nottinghamshire. Understanding how irradiation damage from neutrons affects the mechanical properties of structural materials is a key step towards realising nuclear fusion as a sustainable power source. Without understanding the effect that neutron damage has on the materials there is not realistic method of lifing components hence reactors. However we cannot just build a reactor to test materials and however, working on irradiated materials is costly, and generating mechanical data from them is difficult.

Neutron damage can be simulated with ion irradiations but the damage layers are thin - 200 nm to 100 um. As such traditional mechanical testing methods cannot be used and novel micro-mechanical tests must be conducted. This leads to difficulties in interpreting the results due to size effects inherent in testing small material volumes. Mechanical models are being developed that will include the effect of irradiation damage on the evolving mechanical properties, but these require substantial experimental input in the form of characterisation and mechanistic understanding of how different microstructural features (voids, precipitates, loops) control irradiation induced hardening.

This project will aim to use micromechanical testing on a series of model alloys to deconvolute the effects of different microstructural features. The alloys will be cast with controlled levels of chromium, carbon, and vanadium, to allow control of solid solution, interstitial and carbide strengthening. Samples will be irradiated with both heavy ions and helium to generate voids and dislocations loops. Hardening will be studied using nanoindentation at both room and operational temperatures. Nanoindentation at room temperature is a standard method of studying irradiation hardening but much less work has been carried out on high temperature irradiation hardening using nanoindentation. We expect that using newly developed computational plasticity finite elements methods developed in oxford we will see the effect off irradiation damage not just on yield tress but also work hardening. To understand both the starting microstructure, the microstructural evolution under irradiation and the interaction of the glissile dislocations with microstructural features advanced electron diffraction imaging will be used. This will include diffraction contrast TEM which is well established for studying such microstructures and also transmission Kikuchi diffraction which is much less applied to studying radiation damage but has the advantage of simpler and cheaper imagining equipment. We expected that byt the end of the project we will have gnateatered a range of microstructures, irradiated them, mechanically tested them and related the hardening to the observed microstructures. This will then be inputed to newly developed models at UKAEA.

The project is in collaboration with the UKAEA/Culham Centre for Fusion Energy and the DPhil student will be part of the EPSRC CDT on the Science & Technology of Fusion. The research programme aligns with the EPSRC portfolio themes of both 'Energy' and the sub-themes 'Fusion' and 'Nuclear Power'. The 'Engineering' theme is also relevant through the 'Materials Engineering - Metals and Alloys' research area.