Microstructure and mechanical properties of SiCf/SiC brazed joints

Background: Continuous SiC fiber-reinforced SiC-matrix composites (SiCf/SiC) can be used as the fuel cladding, control rod sheath, intermediate heat exchanger, and tube components for nuclear reactor, the reliability of its joining would be crucial to the safety of nuclear energy. Purpose: This study aims to connect SiCf/SiC with SiCf/SiC using brazing method. Methods: SiCf/SiC was prepared by chemical vapor infiltration (CVI) method. Active brazing method was used to join SiCf/SiC under 850℃, 870℃, and 890℃ with Ag-26.77Cu-4.4Ti (wt. %) filler metal. The microstructure and interfacial phase of the brazed joint under different temperatures were analyzed for a high joining performance using optical microscopy (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The mechanical properties of the brazed joint were analyzed using thermal simulated test machine. Results: The results indicated that AgCuTi filler could realize stable joining for SiCf/SiC, and the surface smoothing of SiCf/SiC was beneficial to improve the shear strength of the joint. Conclusions: When the brazing temperature reached 890 °C, the brittle phase of Ti5Si3 gradually diffused and diffusely distributed to the brazing seam, and the reinforced phase TiC became the main component of reaction layer, which effectively improved the microstructure and significantly increased the strength of the SiCf/SiC brazed joint.