Engineers have developed a new high-performance tungsten-copper metallic coating in one step using plasma spray, for future high heat flux (HHF) plasma facing components (PFC), specifically in the divertor target plate.
The Centre of Excellence in Coating and Surface Engineering (CE-CSE) at the University of Nottingham have demonstrated the successful fabrication of a fully functionally graded tungsten-copper coating using an advanced shrouded atmospheric plasma spraying (APS) technique. This is a first for the scientific discipline to demonstrate how an axial injection plasma spray can be used to build these coatings without the need for a highly specialized vacuum chamber.
The feasibility study was funded by the UK Atomic Energy Agency (UKAEA), and the work was published in the journal Surface and Coatings Technology.
Tungsten and copper are widely used in high-temperature engineering applications because of their complementary properties: Copper efficiently conducts heat away from critical components and tungsten withstands extremely high temperatures and mechanical wear.
However, directly combining the two materials is notoriously difficult. They expand at different rates when heated, which can lead to internal stress, cracking and early failure.
To overcome this, the Nottingham research team engineered a functionally graded coating in which the composition gradually transitioned from copper-rich at the base to tungsten-rich at the surface. Rather than stacking distinct layers, the material changes smoothly across its thickness, reducing stress and improving bonding.
The team successfully produced a coating graded continuously from 0 to 100 weight percent tungsten, achieving a dense and structurally stable material.
The research demonstrated several significant 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 reduced significantly lower than conventional plasma spraying, where oxidation levels are typically much 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 enhanced metallurgical bonding between layers.
The key breakthrough lies in how the coating was produced. 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; however, in conventional systems, the molten particles are exposed to oxygen in the surrounding air, causing oxidation and weakening the material.
The CE-CSE team used a shrouded axial injection atmospheric plasma spray system, which surrounds the plasma jet with a protective gas curtain. This "shroud" acts like a shield around the molten particles, preventing unwanted reactions with air during flight.
In simple terms, the material is sprayed inside a protective bubble, allowing it to solidify in a cleaner and more controlled way. This significantly reduced oxidation and improved coating
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.
Professor Hussain continues: "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 from the UKAEA adds: "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."
