The bonding strength of the sintered alumina is discussed in terms of the bonding conditions, and it is evaluated based on the fracture mechanics concept and the acoustic emission measurement.
The bonding process is obviously promoted with the aid of the binder. From the measurement of the relative density and the observation of the microstructure of the bonding layer, it is found that the bonding strength is improved by the densification of the bonding layer, independent of the thickness of the binder less than 60 μm. The bonding strength increases with increasing the bonding temperature, pressure and holding time up to certain limits, but it increases no longer beyond the limits due to the microstructural damage caused by creep defromation.
By regarding the residual pore in the bonding layer as a crack having an equivalent length, the relationships between the bonding strength and the equivalent crack length can be calculated for the circular shape crack model and the penetrate shape crack model. The measured bending strength of the bonding specimens lie between two curves representing calculated relationships. It is also found that the maximum root-mean-square value of the acoustic emission signal increases with an increase in the bonding strength.