Melting/Solidification of Si Bond Coat Layer in Oxide/Si/RB‐SiC Environmental Barrier Coating System

The effect of melting the Si bond coat layer of a mullite/Si/reaction‐bonded SiC model environmental barrier coating system on the change in its microstructure is studied. Once the Si bond coat layer melts, the molten Si moves toward the RB‐SiC substrate via free Si channels, after which the Si bond coat layer disappears. Just after the onset of solidification of Si, the formation of small spherical Si particles is observed on the surface of the RB‐SiC substrate. This behavior can be attributed to the decrease in the volume of Si owing to a solid–liquid transition and the increase in the volume of Si because of a liquid–solid transition.