Influence of air plasma spraying process parameters on the thermal barrier coating deposited with micro- and nanopowders

This study investigates the optimal conditions to deposit a thermal barrier coating using micro- and nanopowders in the air plasma spraying (APS) process. The influence of the APS process parameters on the thickness, porosity and hardness of the yttria-stabilized zirconia (YSZ; ZrO₂ × 8Y₂O₃) coatings deposited with a single-electrode plasma gun was determined. The temperature and velocity of melted particles were determined by the DPV diagnostic system to decrease the number of experimental processes. The current and H₂ flow rate were changed in this research. Metco-6700 YSZ micropowder has already been used in plasma spray physical vapor deposition. The results of this study suggest the possibility of using it for APS. The particles of this powder are characterized by high temperature (2,700°C–2,900°C) and high speed (>380 m/s). The highest thickness of the coating was obtained with 6 NLPM (normal liter per minute) H₂ flow and 800 A current. Difficulties were observed with the feeding of the powder particles at higher H₂ flow. The results showed that using APS, deposition of Metco-6609, a nanopowder normally used in suspension plasma spraying, is possible. In this research, this powder was fed using a carrier gas. The coatings were around 40 μm thick and had high porosity. The lowest porosity of the coating was obtained at a current of 600 A and H₂ flow rate of 12 NLPM. In the coatings, unmelted spherical particles were also visible.