Interfacial Reactions and Mechanical Properties Studies of C-Coated and C/B4C Duplex-Coated SiC Fiber-Reinforced Ti2AlNb Composites

Abstract

Continuous SiC fiber-reinforced Ti2AlNb 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 SiCf/Ti. In this work, C coating and C/B4C duplex coating were successfully fabricated onto SiC fibers via chemical vapor deposition (CVD), then consolidated into the SiCf/C/Ti2AlNb and the SiCf/C/B4C/Ti2AlNb 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/B4C-dominated interfacial reactions in the SiCf/C/Ti2AlNb and the SiCf/C/B4C/Ti2AlNb were explored, revealing two different reaction products sequences: The different-sized TiC and the coarse-grained (Ti,Nb)C + AlNb3 for the SiCf/C/Ti2AlNb; and the fine-grained TiB2 + TiC, the needle-shaped (Ti,Nb)B2/NbB + (Ti,Nb)C, the coarse-grained (Ti,Nb)C + AlNb2 for the SiCf/C/B4C/Ti2AlNb. Annealing experiments were further carried out to verify the different reaction kinetics caused by C coating and C/B4C duplex coating. The reaction layer (RL)-dominated interfacial strength and tensile strength estimations showed that higher interface strength and tensile strength occurred in the SiCf/C/Ti2AlNb instead of the SiCf/C/B4C/Ti2AlNb, when the same failure mode of fiber push-out took place.