Abstract
Suspension plasma spraying (SPS) process is showing promising improvements for the Thermal barrier coatings (TBCs) performance. This study will focus on the development of a low cost suspension plasma spray system with an axial feeding of yttria stabilized zirconia (YSZ) coatings. A unique twin-cathode plasma spray gun with three plasma torches; P-torch (reversed polarity: cathode nozzle and anode), and two N-torches (normal polarity: anode nozzle and cathode) was used. During operation, the electric power is supplied between P-torch anode and N-torches cathodes to maintain the plasma jet. The system requires only argon as plasma gas, since the enthalpy of plasma jet is enough high for melting ceramic powders, which makes it as cost reduction system. Moreover, the p-torch electrode is hollowed anode and therefore commercial dual tube nozzle was used for the axial feeding to increase the deposition efficiency. It was possible to fabricate dense and/or porous 8YSZ coatings with using only Ar plasma gas through using the twin cathode plasma spray system and the axial injection. The coating microstructure and porosity level can be controlled by appropriate changes in the solids amount in the suspension and the spraying parameters. To control the microstructure the main factor is controlling and adjusting the splat size.
