Cold sprayed tungsten armor for tokamak first wall

Numerous obstacles are still to be resolved before power sources based on nuclear fusion could be employed. One of the major challenges are the materials used for construction of the main reactor vessels. In tokamaks, torus-shaped fusion facilities confining the hot plasma by strong magnetic fields, the inner-most chambers are to be coated with dense coatings of W-based alloys. So far, the attempts for such coatings formation by other methods failed due to oxidation, high porosity, insufficient adhesion, high specific surface, or even insufficient thickness below 10 µm. Cold spraying seems a promising technology for the task. Here we demonstrate a successful fabrication of thick W, W-Cr and W-Cr-Ti coatings prepared without oxidation of the metals. For the first time in history, a deposition of 80 µm-thick coating of pure W was achieved. All coatings exhibited high hardness and good interface quality with different substrates. Oxidation kinetic curves were then measured, suggesting the W-Cr and W-Cr-Ti coatings decreased the oxidation rates compared to pure W. A promising potential for desirable oxidation resistance scales was manifested by formation of complex Cr₂WO_x; importantly, these oxides are not volatile, retaining its function in case of LOCA accident, yielding such coatings acceptable for application.