SiC_f/SiC 钎焊连接微观组织及力学性能研究

[Background] Continuous SiC fiber-reinforced SiC-matrix composites (SiC_f/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 is very crucial to the safety of nuclear energy. [Purpose] This study aims to explore the microstructure and mechanical properties of SiC_f/SiC brazed joints, and optimize processing of connecting SiC_f/SiC with SiC_f/SiC using brazing method. [Methods] SiC_f/SiC was firstly prepared by chemical vapor infiltration (CVI) method, and active brazing method was used to join SiC_f/SiC under 850 ℃, 870 ℃, and 890 ℃ with Ag-26.77Cu-4.4Ti (wt.%) filler metal. Then, 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 & Conclusions] Observation results indicate that AgCuTi filler realizes stable joining for SiC_f/SiC, and the surface smoothing of SiC_f/SiC is beneficial to improve the shear strength of the joint. The reaction between Ti, Si, and C becomes more intense with the increase of the brazing temperature. When the brazing temperature reaches 890 °C, the brittle phase of Ti₅Si₃ gradually diffuses and disperses to the brazing seam, and the reinforced phase TiC becomes the main component of reaction layer, which effectively improves the microstructure and significantly increases the strength of the SiC_f/SiC brazed joint.