Characterization of plasma-sprayed tungsten coating on graphite with intermediate layers

Tungsten (W) coatings were successfully deposited by vacuum plasma spraying (VPS) technique on graphite substrate. Two kinds of intermediate layers were examined to evaluate the interface adhesion between metal W and graphite substrate. Interlayers of silicon carbide (SiC) and titanium (Ti) films prior to the tungsten coating were formed by chemical vapor deposition and sputtering process in order to increase the adhesion strength of coated layers. Tungsten powder with a median size of 10 μm was applied to prepare coatings via a plasma spray system. For VPS processing, argon and hydrogen were used as plasma forming gases, and the coatings were deposited in 35 mbar vacuum pressure. Heat exposure experiment was performed in a sapphire crystal growing furnace hold at 2100 °C for 84 h. After heat exposure, only the Ti interlayered VPS-W coatings were soundly bonded with graphite substrate.