| Abstract: |
Deposition of as-sprayed high crystalline Yb2Si2O7 environmental barrier coatings (EBCs) with controlled secondary phase formation on SiC ceramics is of great interest. This approach can preclude the need for any auxiliary heating during spraying, vacuum chamber, or subsequent heat treatment, leading to considerable cost, time, and energy savings. This research employed atmospheric plasma spray (APS) to deposit Yb2Si2O7 powder on SiC substrates with three different plasma enthalpies. High crystallinity levels in as-sprayed coatings were obtained by precisely adjusting the spray conditions. A desirable microstructure, including a dense, through-thickness crack-free structure with uniform distribution of small pores, was observed in higher enthalpy conditions. On the other hand, the silicon evaporation during spraying led to the formation of a Si-depleted secondary phase (Yb2SiO5) in the final coatings. Decreasing the enthalpy of plasma, while conducive for mitigating the silicon loss, affected the coating microstructure by increasing its porosity and inclusion of partially melted/unmelted particles. It was observed that a slow cooling down after spraying alleviated the microcracking in the coatings but had no significant effect on their crystallinity level. Annealing of the coatings at 1300 °C for 24 hours demonstrated a crack healing effect. Sintering indications were demonstrated in all coatings after annealing at 1300 °C that is close to the normal operating temperature.
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