Functionally Graded Material by Cold Spray for Fusion Energy Devices

In fusion devices, plasma-facing materials are submitted to high heat flux in operating conditions. Tungsten is known as well appropriate as plasma facing material. Actively water-cooled concepts are proposed, involving the use of a metallic structural material such as CuCrZr or lower-activation Eurofer steel. During thermal cycling, the transition zone between outer tungsten and the structural material is submitted to high thermal stresses, due to the mismatch in thermal expansion coefficients. To reduce the stresses and avoid the failure of the system, a functionally graded layer is an effective solution.

Cold spray process allowing both dense coatings and the avoidance of oxide formation appears as promising to join W to CuCrZr or Eurofer. A further difficulty with Eurofer alloy, compared to copper, is its reactivity with tungsten leading to brittle phase formation.

The aim of this work is to investigate the cold spray technique to produce a graded transition between W and copper or Eurofer alloys. Multilayer systems were produced. The microstructure and composition ratio of the coatings as well as the Vickers microhardness were investigated. Graded composition pipes were finally realized to be bonded to W tiles and structural pipe.