A copper plate 2 mm thick has been bonded to an alumina ceramic disk 20 mm in diameter and 7 mm in thickness using an insert metal of titanium foil 0.02 mm thick without external pressure to the bond interface. The bonding has been carried out in a vacuum at a bonding temperature of 1173K above the (lowest) eutectic temperature between copper and titanium.
The thermal stress which is generated in the cooling process after the bonding by the difference in the amount of thermal shrinkage between copper and alumina ceramics has been analysed by the finite element method. The analysis showed that the thermal stress in the ceramics was influenced strongly by the arrangement of the copper and ceramic specimens: the thermal stress in the ceramics became much lower when a couple of ceramic specimens were bonded to both sides of a copper plate (symmetric arrangement) than when a ceramic specimen was bonded to one side (asymmetric arrangement).
In fact, cracks initiated at the periphery of the bond interface were observed in the ceramics for the asymmetric arrangement. A joint of the symmetric arrangement could be cut into two joints (copper-bonded alumina ceramics) of the asymmetric arrangement without any crack. The copper-bonded alumina ceramics obtained could be brazed successfully to a mild steel using filler metal of BAg8 (JIS).
