Enabling sustainable fusion and other power generation technologies by novel manufacturing

Civil fusion power concepts that offer zero carbon energy at nation-scale are maturing, and the UK has a leading position through its novel Spherical Tokamak for Energy Production (STEP) concept. STEP requires tungsten reactor coatings to provide a critical protection for copper and steel-based plasma facing components because no other material can offer tungsten mix of thermophysical properties, including high melting point, high thermal conductivity and erosion resistance to plasma strikes that cannot be avoided. However, fabrication of thick tungsten coatings on copper or steel reactor vessel is challenged by the large difference in their melting points and thermal expansion coefficients that leads to severe thermal expansion mismatch strains and premature failure during manufacture and inevitable in-service thermal fluctuations. Current tungsten coating manufacturing routes cannot produce coatings of sufficient thickness (multi-millimetre) and lifetime (> 3 years) for sustainable commercial applications.

This project will address the manufacturing challenges by researching a new workflow based on 3D printing (3DP) and other approaches to create powder-based graded layers, followed by field assisted sintering (FAST). FAST is an advanced rapid powder consolidation technique.

Although applied for W coatings, the new approach will be applicable to a wide range of technologically important dissimilar coating/substrate systems for clean energy solutions. The novelty lies in several interlinked areas:

- 3DP with topographically patterned substrate surfaces, with no waste of metallic powders, for controlled strain relief by introducing regulated micro-cracking;
- Use of multi-material interlayers between steel and W layers, including complex geometries and/or a transitory liquid phase sintering material;
- Technology for effective polymer debinding of printed 3D multi-structures as an integrated part of the FAST workflow;
- Process simulations of the underlying physics including the evolution of stresses and strains, cracking and failure modes, and detailed microstructural characterisation of the novel multi-material structures; and
- Access to specialised plasma reactor simulators to test and optimise coatings and components under realistic conditions.

We aim to develop new capabilities and exploit the associated understanding to produce a generic manufacturing platform for tailored coatings systems for fusion and other low carbon power applications.

The overall project objectives are:
- To develop a new, scalable manufacturing process workflow for the fabrication of mm-scale tungsten coating on a range of materials for fusion energy applications, including steels and CuCrZr alloys;
- To extend the methodology to curved surfaces and structural components with complex geometry;
- To fabricate industrial scale demonstrator components for fusion applications.

The project will last the length of a fusion CDT studentship and build on the research knowledge we have accumulated over the last 10 years on joining dissimilar materials. It will also link more broadly with the body of fusion research within the Department of Materials , Oxford.

This project falls within the EPSRC manufacturing the future and nuclear fusion research area. The project is in collaboration with Dr. Fritsch (Germany), which is an advance machines and materials manufacturer.