Effect Of Particles In-Flight Properties On Microstructure And Properties Of Plasma Sprayed Yttria-Stabilized-Zirconia Coating

Yttria stabilized zirconia（YSZ）thermal barrier coating（TBC）prepared by atmospheric plasma spraying（APS）technology has broad application foreground in many industry fields such as aerospace,transportation and petrochemical,etc.for its low cost,high efficiency,low thermal conductivity,high thermal stability and so on.In this article,TBC was fabricated by supersonic atmospheric plasma spraying（SAPS）,in which the top ceramic was YSZ coating and the bond coating was NiCoCrAlY.The effect of spraying power,percent of H₂ flow rate and powder size on the YSZ particle in-flight melting state was analyzed.Meanwhile,the YSZ particles in-flight physicochemical properties during SAPS and spreading behavior on substrate were investigated.The microstructure,mechanical properties and thermal resistant properties of coatings were respectively experimented and analysed by relative characterization and technology.The results showed that:（1）The surface temperature and average velocity of the particles in-flight increase gradually with the increase of spraying power and the average velocity slowly increases when spraying power is higher than 60 kW.The surface temperature of the particles in-flight increase gradually with the increase of H₂ flow rate,while the average velocity decrease gradually.Both the surface temperature and average velocity of finer powder are higher than conventional powder’s when the spraying parameters are same.（2）The melting index of the particles in-flight increases and then decreases with the increase of spraying power.Higher or lower power has have negative effect.The melting index of the particles in-flight increases gradually with the increase of H₂ flow rate.The melting state of finer powder is better than conventional powder’s when the spraying parameters are same and the experiment results are reported to verify the correctness of theory calculation.（3）Powders injected into the SAPS plasma jet are quickly heated and melted companied with breakup and collision-coalescence and the inside is dense with hollow structure.The content of zirconium（Zr）and yttrium（Y）element decreases and phase transits.（4）The particles in-flight with better melting state have higher deposition efficiency and the morphology of splat is mainly disk-like with better combination condition between splat and substrate and splat-splat.However,the particles in-flight with worse melting state have lower deposition efficiency and the morphology of splat is irregular and mainly bump-like with worse combination condition between splat and substrate and splat-splat.（5）The improvement of melting state of the particles in-flight is helpful to improving the density of the as-sprayed coating and lowing defects such as pore,crack,etc.Compared with the coatings made by particles in-flight with worse melting state,the coatings made by particles in-flight with better melting state have continuous columnar crystals.The microstructure of the coating is more complex and the properties of mechanical,heat insulation,oxidation resistance and thermal shocking resistance of coatings are better.