Microstructure and properties of SiCf/SiC joint brazed by Y-Al-Si-O glass

In this study, SiC fiber reinforced SiC ceramic matrix composites (SiCf/SiC) were joined by Y-Al-Si-O glass. The effects of the composition of Y-Al-Si-O glass, brazing temperature and holding time on microstructure and properties of SiCf/SiC joint were investigated. Based on the investigated results, the brazing process was optimized. The results showed that the wettability of Y30 glass (SiO2 55 wt%, Al2O3 15 wt%, Y2O3 30 wt%,) and SiCf/SiC was good and the wetting angle was similar to 9.84 degrees. With the increase of the temperature from 1300 degrees C to 1400 degrees C, the crystal phase decreased and Y-Al-Si-O glass phase increased gradually in the joint brazed by Y30 glass. The joint layer brazed by Y30 glass at 1400 degrees C contained only amorphous phase, and the joint layer with smooth and defect-free structure is beneficial to its airtightness. The shear strength of the joint brazed by Y30 glass increased with the increase of the brazing temperature from 1300 degrees C to 1400 degrees C, and the shear strength reached the maximum at 1400 degrees C. The effect of holding time on the shear strength of the joint brazed by Y30 glass at 1400 degrees C was largely insignificant. The optimized joining process of the SiCf/SiC brazed by Y-Al-Si-O glass was that the brazing agent is Y30 glass, the brazing temperature and the holding time were 1400 degrees C and 0 min, respectively. With optimized process, the shear strength of the joint was 38.85 MPa. With the increase of thermal shock times, the shear strength of the joint with optimized process declined gradually because the cracks occurred in the interface near the SiCf/SiC and gradually propagated to the joint layer.