Microstructure evolution and high-temperature mechanical properties of SiCf/SiC composites in liquid fluoride salt environment

- Corrosion behavior of SiCf/SiC CMCs in fluoride salt was studied.
- O-contained boundaries result in the non-uniform corrosion of SiC matrix.
- The SiF coordinate bond plays important roles in SiC corrosion.
- Corrosion damage of matrix leads to degradation of mechanical properties.

High temperature mechanical properties and microstructure evolution of chemical-vapor-infiltrated SiC fiber reinforced SiC ceramic matrix composites (SiCf/SiC) in 46.5LiF-11.5NaF-42.0KF (mol.%, FLiNaK) eutectic salt were investigated. The results indicate that the corrosion of SiCf/SiC composites was accelerated with increase of corrosion temperature. Interlayer boundaries in SiC matrix with higher oxygen content were corroded preferentially. The F− formed SiF coordinate bond with SiC and replaced carbon, followed by the corrosion of SiC matrix. While single SiC fiber tensile strength suffered no depravation after corrosion, corrosion and damage of SiC matrix led to deteriorated high temperature mechanical properties of SiCf/SiC composites.