Spatial mapping of hydrogen in coatings for fusion using Atom Probe Tomography to inform modelling of tritium trapping

Future fusion reactor designs such as DEMO and STEP will need to breed large quantities of tritium fuel and maintain tritium inventory to ensure safe and efficient plant operation.

Thin (micron-scale) multilayer coatings are one way to control tritium diffusion, which is vital to prevent tritium loss, and these are an active area of materials development. A ceramic oxide or nitride tritium permeation barrier (TPB) basecoat is applied to structural materials, followed by a liquid metal-facing topcoat to provide corrosion resistance. Erbia and yttria TPBs have acceptable chemical compatibility with Li, and perform well with permeation reduction factors (PRFs) greater than 1000. However, experimental measurements of PRFs in the literature can vary, and are often orders of magnitude lower than theoretical predictions, making it difficult to accurately predict and validate coating performance. One reason for this is a limited understanding of hydrogen trapping and transport behaviour within such ceramics, which could be addressed through quantification and spatial mapping of tritium within the coating and at the coating-substrate interface. One technique capable of this is Atom Probe Tomography, which has previously shown the ability to quantify and map hydrogen at microstructural features in steel and tungsten.

This project will apply APT to coatings to address the knowledge gap around tritium trapping in ceramics. Coated samples will be exposed to hydrogen isotopes through ion driven exposures and gas soaking methods at UKAEA. The project will make use of cryogenic sample preparation and vacuum transfer procedures developed by Oxford and UKAEA, aimed at minimising hydrogen isotope loss during such treatments. The APT quantification and spatial mapping results will be benchmarked by thermal desorption spectroscopy (TDS) and secondary ion mass spectrometry (SIMS). APT data will also be complemented by first principle modelling from UKAEA colleagues to aid interpretation and ultimately improve coating lifetime predictions and reactor designs.

Materials to be studied will include alumina, erbia, yttria and novel coatings developed in house within UKAEA. Experimental techniques the student will utilise include scanning electron microscopy (SEM), focused ion beam (FIB) micromachining and atom probe tomography (APT). The student will also have the chance to liaise closely with researchers working at UKAEA.

Project will be co-supervised by Dr. Hazel Gardner and Dr. Benjamin Jenkins (UKAEA).

NB: Expected funding arrangements for this project are currently being finalised