Preparation and Characterization of Thick Tungsten Coatings for Plasma Facing Materials

Abstract:

Plasma spray (PS) is the dominant technology for preparing tungsten (W) coatings used as plasma facing materials (PFM). Two types of tungsten powders, i.e. crystal tungsten powder and carbonyl tungsten powder, produced by different methods, were adopted during plasma spray. Three thick tungsten coatings with thickness of 3-4 mm on copper-chromium-zirconium (Cu, Cr, Zr) alloy substrate with 110 mm × 130 mm were fabricated by means of atmospheric plasma spray (APS). The CuMo/MoW was used as the interlayer of tungsten coatings. Characterization of coatings was performed in order to assess microstructure, mechanical and thermal properties. The results indicate that the coating from carbonyl tungsten powder has better over-all properties than that from crystal tungsten powder, and for the coatings from the same powder, the thin coating possesses higher bond strength than the thick. The porosity of the coating is less than 2% by digital image analysis. The maximal tensile strength value of coatings is about 10 MPa. The content of oxygen is about 6 wt% by EDS. The maximal thermal conductivity of the pure tungsten coatings is 12.52 W/(m·K). The high oxygen results in the low thermal conductivity of the tungsten coating. The work performed has demonstrated the feasibility of 3-4 mm thick W coatings on flat geometries by APS, which is the foundation of preparing the low cost and high property thick tungsten coatings.

Key words:tungsten; coating; plasma spray; plasma facing materials; nuclear fusion