Preparation And Characterization Of W Coatings Prepared By Low Pressure Plasma Spraying

Low Pressure Plasma Sprayed physically stable W coating on the CrZrCu heat sink material was considered as one of ideal PFMs(Plasma Facing Materials, PFMs). However, the application of such structure was greatly affected by the properties of W coating, including oxygen content and porosity and thermal conductivity. The high oxygen content, high porosity can reduce the conductivity of W coating, which weaken the capatility of thermal conductance and finally leds to the failure of first wall material.The deposition of W coating on copper substrate was carried out via LPPS process in this paper. The plasma gun and feedstocks were selected. The powder feeding mode, plasma gun power and deposition pressure were optimized. The coating microstructure and properties for W coatings were characterized by SEM, XRD and oxygen nitrogen analyzer, and the effects of process parameters on the coating microstructure and properties were discussed.The following conclusions could be drawn:1) The deposition efficiency for W coatinged eposited by conventional F4 gun was just 35%, and many unmelted W particles were observed in the coating. Using the improved of F4–M gun in gun nozzle, deposition efficiency over 60% have been obtained and unmolten particles were invisible in the coating. Particles with size ranging from 15 to 30 micron can get fully melted in the plasma plume and completely fattened on the surface of substrate. The porosity for W coating with 15～30 micron W powder as feedstock was lower than 2%. Based on the above researches, the W powder was selected as feedstock for further study.2) W coating obtained with inside powder feeding mode was obviously inferior to the coating prepared by with outside powder feeding. When the plasma gun power reached 35kW, the density for W coating prepared with 15～30μm powder was over 98%. The coating microstructure and properties were strongly affected by the deposition pressure. The porosity and oxygen content for W coating was much lower than other coatings when the deposition pressure was 200 or 300 torr.3) Thermal conductivity for thick W coating directly deposited on the large area copper alloy substrate was 110.76W/m·K, and the pores for the coating was dominated by the micron pore size. The microstructure and properties of coating are better than other processe. Preheat of substrate over 60℃prevented from the coating crack as a result of qunching of W particle.The optimiz deposition process for W coatings are as follow: the F4-M spray gun and W powder with particle size ranging from 15 to 30 micron are selected as feedstock. The plasma gun power is 35kW and the deposition pressure is 200 torr. Using these excellent W coatings can obtain.