Tungsten Coatings for Nuclear Fusion Applications – materials strand project

Supervisor/s: Dr Ying Chen and Dr David Hall (University of Manchester), & Dr James Wade-Zhu (UKAEA)

The first-wall of a fusion reactor is the primary layer that protects the structural materials from the extreme temperatures generated in the fusion plasma. This application requires materials with high resistance to extreme heat fluxes and temperatures (20-25 MWm-2 or 2200-2800°C bursts) as well as sputtering erosion caused by incident particles bombarding the first-wall surface during plasma disruptions. After many years of research, tungsten has emerged as the most promising material for existing experimental and future commercial fusion reactors. Tungsten offers a range of outstanding material properties including a very high melting point, high thermal conductivity, low thermal expansion and low activation. Unfortunately, pure tungsten is hard, brittle and difficult to machine, bringing with it key technological challenges and increased cost in its bulk manufacture.

An alternative approach to tackle this manufacturing challenge is to apply tungsten as a coating onto reactor components. The advantage of coatings is that they are low-cost, microstructurally-tailorable and can be re-applied to repair damaged sections of the first-wall, e.g. after material loss due to evaporation and/or sputtering effects. However, many conventional coating methods such as thermal spray, physical vapour deposition (PVD) or chemical vapour deposition (CVD) have intrinsic problems in manufacturing tungsten coatings. For example, thermally sprayed coatings are usually porous and suffer material loss in the manufacturing process due to oxidation and evaporation. PVD and CVD are costly and cannot deposit thick coatings. As a result, a new coating method is needed to bridge this gap.

This project aims to develop a new method called aerosol deposition to manufacture tungsten and tungsten composite coatings for fusion first-wall applications (demonstration in Fig. 1a). Aerosol deposition is a novel coating process in which fine powder is mixed with a carrier gas to form an aerosol flow, ejected through a micro-orifice nozzle and deposited onto a substrate in a vacuum chamber. The method can be used to deposit non-metal, metal, thin and thick layers and has several advantages such as room temperature processing, suitability for mass production, direct deposition and low-cost. Powder mixes can also be deposited and optimised to produce doped and/or particle-reinforced microstructures that are more stable under high heat-loads by inhibiting tungsten recrystallisation. These features make aerosol deposition a promising method to deposit tungsten-based coatings for fusion applications.

The objectives of the project include:

  1. Develop and optimise an aerosol deposition to produce high-density, mm-thick tungsten and tungsten composite coatings,
  2. Determine the mechanical and thermal properties of the coatings at fusion-relevant temperatures,
  3. Irradiate coatings to understand changes in their performance under simulated fusion conditions,

The coating process development will be based on the newly-established aerosol deposition facility in the Henry Royce Institute at Manchester. The crystallinity and microstructures of the coatings will be studied by XRD, SEM and TEM. Key properties will be collected using advanced techniques, including cutting-edge in-situ micro-mechanical testing (see Fig. 1b) in the Henry Royce Institute and UKAEA. UKAEA will also support irradiations of the coatings at fusion-relevant temperatures, leveraging high-energy ion beam capabilities at the Dalton Cumbria Facility to introduce irradiation-induced defects into the coating surfaces. Post-irradiation micro-mechanical testing will be repeated at the Henry Royce Institute or UKAEA. The successful development of aerosol deposition of tungsten and tungsten composite coatings will provide a potential material solution for plasma facing materials in fusion reactors.

The project will be mainly based in Manchester but will involve travel to UKAEA for meetings and experiments. There will be opportunities for travel to conferences and collaborations with other groups.

This project is offered by University of Manchester. For further information please contact: Ying Chen (ying.chen-2@manchester.ac.uk), David Hall (david.a.hall@manchester.ac.uk) & James Wade-Zhu (james.wade-zhu@ukaea.uk).

This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.

Image above: Left: a dense coating made by aerosol deposition; Right: micromechanical testing of coatings