Fast interdiffusion and Kirkendall effects of SiC-coated C/SiC composites joined by a Ti-Nb-Ti interlayer via spark plasma sintering

SiC-coated 3D C/SiC composites were successfully joined with a Ti-Nb-Ti interlayer by SPS. When joined at 1200 °C, the apparent shear strength of the samples was as high as 61 ± 6 MPa as a result of an appropriate interface diffusion reaction. However, higher joining temperature (1600 °C) resulted in significantly lower shear strengths, and this was associated with the observed depletion of Si atoms and Kirkendall voids at the joining interface. Subsequently, a detailed characterization was performed by FIB/TEM/STEM. The interdiffusion mechanism of the samples during the joining process was revealed by thermodynamics and diffusion kinetics, and different interdiffusion mechanisms were associated with the evolution of the phase composition. The micro voids formed via Kirkendall effect were observed to grow rapidly with the joining temperature, resulting in catastrophic joint failure. Finally, these results were used to propose a failure model for the joints.