Interfacial Reactions and Mechanical Properties Studies of C-Coated and C/BC Duplex-Coated SiC Fiber-Reinforced TiAlNb Composites.

Continuous SiC fiber-reinforced TiAlNb matrix composites have a great potential for high-temperature aviation structure applications, and their properties strongly depend on the microstructure of the interfacial reaction layer. Notably, introducing diffusion barrier coatings has still been a popular strategy for optimizing the interfacial structure and interfacial properties of SiC/Ti. In this work, C coating and C/BC duplex coating were successfully fabricated onto SiC fibers via chemical vapor deposition (CVD), then consolidated into the SiC/C/TiAlNb and the SiC/C/BC/TiAlNb composites, respectively, via hot isostatic pressing (HIP) under the condition of 970 °C, 150 MPa, 120 min, and finally furnace cooled to room temperature. The C- and C/BC-dominated interfacial reactions in the SiC/C/TiAlNb and the SiC/C/BC/TiAlNb were explored, revealing two different reaction products sequences: The different-sized TiC and the coarse-grained (Ti,Nb)C + AlNb for the SiC/C/TiAlNb; and the fine-grained TiB + TiC, the needle-shaped (Ti,Nb)B/NbB + (Ti,Nb)C, the coarse-grained (Ti,Nb)C + AlNb for the SiC/C/BC/TiAlNb. Annealing experiments were further carried out to verify the different reaction kinetics caused by C coating and C/BC duplex coating. The reaction layer (RL)-dominated interfacial strength and tensile strength estimations showed that higher interface strength and tensile strength occurred in the SiC/C/TiAlNb instead of the SiC/C/BC/TiAlNb, when the same failure mode of fiber push-out took place.