Microstructural Change during Heat Exposure in Air of Modeled Environmental Barrier Coating Processed by Aerosol Deposition Method

Abstract

Optimal deposition parameters for the aerosol deposition of a β-SiAlON coating and the microstructure change of an EBC after heat exposure in air are investigated. Dense and crystalline SiAlON coating having developed texture, where the (0001) plane is declined approximately 10° from the coating plane is formed. The deposition rate increases with the gas flow rate when the rate is ranging from 12 to 16 L/min. Further increase of the gas flow rate decreases the deposition rate. Regarding the 15 µm thick mullite coating deposited on SiAlON substrate heat exposed at 1573 K over 30 h, delamination of the coating occurs due to the oxidation of SiAlON. 30 µm thick mullite coating prevents the oxidation. As for the EBC deposited on Si–SiC substrate, delamination occurs at Si–SiC/SiAlON interface by the oxidation of SiC during heat exposure at 1573 K. At the bonded region during heat exposure, SiAlON prevents the mullite coating to become (SiO₂+mullite) two-phase state by supping Al to the mullite. Residual Si at the substrate moves to SiAlON and mullite coating under heat exposure at 1673 K. Structure of EBC is maintained by using SiC substrate in which the Si will not move to the coating during exposure.

 

This Paper was Originally Published in Japanese in J. Japan Thermal Spray Soc. 57 (2020) 88–96.

Fig. 11 SEM micrographs and EDX maps showing a cross-section of a modeled EBC deposited on a SiC substrate. EDX maps showing the distribution of the Si, Al, O and N elements. The distribution of the elements is represented by shading. The as-deposited EBC specimens (a), (b) were heat exposed in air at 1673 K for (c), (d) 10 h.