Interfacial microstructures and bonding strength between aluminum nitride and silver brazing filler metals containing various active elements

Effect of active element on interfacial microstructures and bonding strength of brazed AIN/AIN joints has been investigated and compared with the case of brazed Si₃N₄/Si₃N₄ joints. Brazing was carried out at 1173 to 1473 K for 3.6 ks in a vacuum using Ag-Cu filler metals containing Ti, Zr, V and Nb as an active element. The obtained joint had no defects such as un-bonded areas, regardless of active element and bonding temperature. Four kinds of active elements were divided into two groups by shear tests and microstructural observations. One was Ti and Zr, and the other was V and Nb. The bonding strength of the former was higher than that of the latter. In particular, the joint with Ti addition showed an excellent strength of about 200 MPa. Main fracture position in the joints with Ti and Zr additions was within the AIN, while most joints with V and Nb additions broke at the interface between the active filler metal and the AIN. In the former, TiN and ZrN layers consisting of fine grains were observed adjacent to the AIN. On the other hand, the joint with Nb addition had roundish grains of Nb ₂N in similar locations. It was considered that the existence of fine grains contributed to the enhancement of bonding strength due to the increase of contact area and to the formation of complicated interface. These tendencies were essentially consistent with those of the brazed Si₃N ₄/Si₃N₄ joints.