For future high heat flux plasma-facing components
Engineers have developed a new, high-performance tungsten-copper metallic coating in a single step via plasma spray for future high heat flux (HHF) plasma-facing components (PFCs), particularly the divertor target plate
The Centre of Excellence in Coating and Surface Engineering (CE-CSE) at the University of Nottingham have revealed the successful fabrication of a fully functional graded tungsten-copper coating using an advanced shrouded atmospheric plasma spraying (APS) technique. This is the first time the scientific discipline has demonstrated how an axial injection plasma spray can help build these coatings without a highly specialised vacuum chamber.
The UK Atomic Energy Authority (UKAEA) funded the feasibility, and the work was published in the journal Surface and Coatings Technology.
Tungsten and copper are often utilised in high-temperature engineering applications because of their complementary properties. Copper can efficiently conduct heat away from critical components, whereas tungsten withstands extremely high temperatures and mechanical wear.
Directly combining the two materials is notoriously difficult as they expand at different rates when heated, which can cause internal stress, cracking, and early failure.
To overcome this, the research team designed a functionally graded coating in which the composition gradually transitioned from copper-rich at the base to tungsten-rich at the surface. Instead of stacking layers, the material changes smoothly across its thickness, reducing stress and improving bonding.
The team produced a coating graded continuously from 0 to 100 weight per cent tungsten, resulting in a dense, structurally stable material.
The research demonstrated several performance improvements, including ultra-low porosity compared to typical atmospheric plasma spray coatings. Lower porosity means fewer weak points and greater durability. Copper oxide content was significantly lower than in conventional plasma spraying, where oxidation levels are typically higher and lead to a progressive increase in hardness across the coating thickness.
Post-spray heat treatment further reduced microcracks in tungsten-rich regions and improved metallurgical bonding between layers.
The key breakthrough is how the coating was created. Plasma spraying works by injecting powdered metal into a high-temperature plasma jet, where it melts and is projected onto a surface to form a coating; but in conventional systems, the molten particles are exposed to oxygen in the surrounding air, leading to oxidation and weakened material.
The team used a shrouded axial injection atmospheric plasma spray system, which surrounds the plasma jet with a protective gas curtain. This ‘shroud’ acts as a shield around the molten particles, preventing unwanted reactions with air during flight.
Professor Tanvir Hussain from the University of Nottingham’s CE-CSE, said, “The ability to produce dense, graded copper–tungsten coatings have important implications for industries operating in extreme environment in space, aerospace and fusion sectors. Copper-tungsten components are essential for the UK to realise the ambition of cleaner fusion energy. Our plasma spraying technique adds a promising step to bring fusion energy one step closer to reality.
“By reducing oxidation, minimising porosity and tailoring mechanical properties across the coating thickness, the technology could extend component lifetimes, improve reliability and reduce maintenance costs.”
Dr Benjamin Evans, UKAEA, said, “Tungsten is a vital part of virtually all tokamaks; its high melting point is a blessing for plasma-facing components, but difficult for manufacturers to work with.
“The UKAEA Manufacturing Technology and Equipment Qualification (MTEQ) group and Materials Division are always looking for novel joining techniques and better ways to produce tungsten components. Joining dissimilar materials to one another is a complex challenge and extremely important in realising commercial fusion. The work that the University of Nottingham have demonstrated is a fantastic step towards bringing fusion energy to the UK.”
