Microstructures and Deteriorations on Al_2O_3/Al Alloy Joints
The deterioration behavior of Al<SUB>2</SUB>O<SUB>3</SUB>/Al-alloy interlayer bonding interfaces when immersed in molten Na were investigated. Two Al<SUB>2</SUB>O<SUB>3</SUB> cylinders were bonded in a vacuum bonding facility using an Al alloy interlayer, at a bonding temperature and compression of 590°C and 10MPa, respectively. After simple immersion or thermal cycling while immersed in molten Na or in air, four-point bending tests were executed. The cracks on the bonding interfaces were investigated. The results showed that Na had penetrated into the specimens that underwent immersion, and that the Al<SUB>2</SUB>O<SUB>3</SUB>/Al bonding interface seemed to be more susceptible to damage than Al and Al<SUB>2</SUB>O<SUB>3</SUB> themselves. Bending strength declined remarkably after thermal cycling while immersed. On the other hand, it scarcely declined during cycling in air. Striations observed on the fracture surface enabled us to measure the crack growth rate during the while-immersed thermal cycling, and thermal stresses found to promote the propagations of the cracks. The results of observation by transmission electron microscope (TEM) and analysis by energy dispersive X-ray analyzer (EDX) indicated that certain kinds of impurities concentrated on and near the bonding interface. It seems likely that some of these impurities weakened the bonds and others dissolved easily in the molten sodium, so we believe the concentrations of the impurities to be one of the causes of deterioration.
- Materials transactions, JIM
Materials transactions, JIM 37(5), 1127-1131, 1996-05