Effect of active metal on bonding characteristics and interfacial structure of the Si₃N₄/Si₃N₄ joints brazed by Ag-Cu filler metal

Joining of Si₃N₄ to Si₃N₄ was carried out using Ag-Cu filler metal containing Ti, Zr, V and Nb as an active metal. Bonding treatment was performed at 1173 to 1473 K for 1h in a vacuum. The shear strengths of the joints brazed at 1173 to 1473 K using active filler metals containing Ti and Zr were 150 to 250 MPa. The fracture position of the joints after shear test was the filler metal or mixture of the filler metal and Si₃N₄. On the other hand, the average shear strengths of the joints brazed at 1373 K using active filler metals containing V and Nb were 144 and 163 MPa, respectively. The fracture position of the joints using these filler metals was the interface between filler metal and Si₃N₄ in all cases. The active filler metals containing Ti and Zr yielded TiN and ZrN fine grains close to the Si₃N₄. No fine grains were observed in the joint using active filler metal containing V and coarse columnar grains of V₃Si were observed. Therefore, it is concluded that the fine grains of the nitrides formed close to the Si₃N₄ is responsible for the substantial bonding between filler metal and Si₃N₄.