Mullite and mullite/ZrO2-7wt.%Y2O3 Powders for Thermal Spraying of Environmental Barrier Coatings

Mullite and Mullite/ZrO₂-7wt%Y₂O₃ coatings could be thought among the main protective layers for environment barrier coatings (EBCs) to protect Si-based substrates in future gas turbine engines. Most of the target compositions are not presently available. In this study, different powder processing routes as Spray Drying, (SD), Freeze Drying (FD), and Flame Spheroidation (FS) are compared. The influence of the powder production technique on the particle size, the morphology and microstructure of the powder particles was investigated. In addition, different thermal treatments were performed to increase the grain cohesion to enhance the powders flowability. The effect of the heat treatments on the powder crystallinity and microstructure was also evaluated. These powders were plasma-sprayed and their in-flight particles characteristics monitored. Splats deposited on SiC substrates were collected and analyzed via scanning electron microscopy (SEM). A correlation among powder morphology, in-flight particle characteristics and splat morphology was established in order to better understand the influence of the powder processing route on the coating formation.