Abstract:The joining of porous Si 3 N 4 to dense Si 3 N 4 ceramics has been successfully performed using mixed RE 2 O 3 (RE = Y or Yb), Al 2 O 3 , SiO 2 , and α-Si 3 N 4 powders. The results suggested that the α-Si 3 N 4 powders partly transformed into β-SiAlON and partly dissolved into oxide glass to form oxynitride glass. Thus, composites of glass/β-SiAlON-ceramic formed in the seam of joints. Due to the capillary action of the porous Si 3 N 4 ceramic, the molten glass solder infiltrated into the porous Si 3 N 4 ceramic side during the joining process and formed the "infiltration zone" with a thickness of about 400 µm, which contributed to the heterogeneous distribution of the RE-Si-Al-O-N glasses in the porous Si 3 N 4 substrate. In-situ formation of β-SiAlON in the seam resulted in a high bonding strength. The maximum bending strength of 103 MPa and 88 MPa was reached for the porous Si 3 N 4 /dense Si 3 N 4 joints using Y-Si-Al-O-N and Yb-Si-Al-O-N glass solders, respectively.

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In this paper, 49.77wt.% CaO-50.23wt.% Al2O3 (CA) glass has been designed, fabricated and studied for the joining of SiC ceramics. The thermophysical properties, crystallization kinetics, crystallization behavior of glass solder, and the microstructure of the joint were analyzed and discussed in detail. It is found that the melting point of CA glass solder is 1437 °C, the crystallization activation energy is 274.07 kJ/mol, and the precipitated crystal is 12CaO·7Al2O3. The minimum wetting angle of CA solder on pre-oxidized SiC ceramics is 23°. The joint interface is well combined, and two crystal phases of 2CaO·Al2O3·SiO2 and 12CaO·7Al2O3 are formed in the weld. The typical microstructure of a SiC ceramic joint with CA glass solder is SiC/2CaO·Al2O3·SiO2+12CaO·7Al2O3/SiC at 1550 °C for 10 min.