Microstructure evolution and mechanical properties of porous Si3N4 and dense Si3N4 joints bonded using CaO Li2O-Al2O3 SiO2 glass-ceramic

A novel CaO-Li2O-Al2O3-SiO2 (CLAS) glass was developed for the joining of porous Si3N4 and dense Si3N4. A multiphase interlayer consisting of CaAl2Si2O8, LiAlSi2O6 and CaSiO3 phases was formed in joint, which possessed matched CTE with the Si3N4 substrates. In addition, the infiltrated layer with bilayer structure in the porous Si3N4 substrate was observed. The effects of joining temperature and cooling rate on microstructure, phase evolution and shear strength of joints were studied carefully. The results showed that the kinds of precipitated phases remained invariable with the joining temperature increased, but the crystallinity in the interlayer was improved remarkably as the cooling rate reduced. The maximum shear strength of 45 MPa was obtained when the joining temperature and cooling rate were 1100 degrees C and 5 degrees C/min, respectively. Moreover, fracture during the shear test occurred mainly within porous Si3N4 side, indicating superior joining of dense Si3N4/glass-ceramic/porous Si3N4.