Particle in-flight behavior and its influence on the microstructure and properties of supersonic-atmospheric-plasma-sprayed nanostructured thermal barrier coatings

In order to accurately control the microstructure and property of yttria-partially-stabilized-zirconia (YPSZ) coatings, this paper elaborated the particle in-flight behavior during supersonic atmospheric plasma spraying (SAPS) and its significance in determining the microstructure and thermal insulation properties of SAPS-YPSZ coatings. The results suggested that, for a Laval nozzle with an internal injection port, the influence of spray power on the particles velocity is more significant than the temperature. When the spray power and argon flow rate were kept unchanged, the increase of hydrogen percentage in the mixed plasma gas can increase the temperature while decrease the velocity. Compared with other spray parameters, the standoff distance had the most significant influence on both the temperature and velocity of in-flight particles. The particles temperature and velocity determined the melting state of particles and the content of unmelted nanoparticles of as-sprayed coatings, which decreased from 12% to 6% when the particles temperature and velocity increased by 10% and 14%, respectively. For a 300-μm-thick YPSZ coating, thermal insulation temperature increased from 69 °C to 90 °C (increased by 30%) when the unmelted nanoparticle content increased from 6% to 12%.