Microstructure and properties of SiCf/SiC composite joints with CaO-Y2O3-Al2O3-SiO2 interlayer

Using CaO, Y2O3, Al2O3, and SiO2 micron-powders as raw materials, CaO-Y2O3-Al2O3-SiO2 (CYAS) glass was prepared using water cooling method. The coefficient of thermal expansion (CTE) of CYAS glass was found to be 4.3 x 10-6/K, which was similar to that of SiCf/SiC composites. The glass transition temperature of CYAS glass was determined to be 723.1 degrees C. With the increase of temperature, CYAS glass powder exhibited crystallization and sintering behaviors. Below 1300 degrees C, yttrium disilicate, mullite and cristobalite crystals gradually precipitated out. However, above 1300 degrees C, the crystals started diminishing, eventually disappearing after heat treatment at 1400 degrees C. CYAS glass powder was used to join SiCf/SiC composites. The results showed that the joint gradually densified as brazing temperature increased, while the phase in the interlayer was consistent with that of glass powder heated at the same temperature. The holding time had little effect on phase composition of the joint, while longer holding time was more beneficial to the elimination of residual bubbles in the interlayer and promoted the infiltration of glass solder into SiCf/SiC composites. The joint brazed at 1400 degrees C/30 min was dense and defect-free with the highest shear strength of about 57.1 MPa.

Automated summary

The study investigated the joining performance of CYAS glass powder sintered under different temperature conditions with SiCf/SiC composites. The joint prepared under 1400 degrees C/30 min condition was the densest, defect-free, with the highest shear strength.