Effect of heat treatment and residual stress due to contact deformation on fracture behavior of Al/sapphire joint fabricated by SAB

Surface activated room temperature bonding (SAB) has been proposed as a new process which can overcome many problems caused by traditional high temperature bonding. For an application of this technology, it is expected to elucidate mechanical properties and fracture behavior under the environment where it is supposed to be used. In this study, tensile tests were conducted for a Al/Sapphire joint cyclic heat treated to 400 degrees C. That brought about increase of bonding strength, which provides SAB process with good outlook for application. We pursued an analysis including residual stress by combination of FEM calculation and experimental observations. The findings of this research are summarized as follows. Softening of bulk Al due to heat treatment increased the bonding strength by decreasing stress concentration, but the ultimate tensile strength of the joint remained constant. Specimens held at high temperature for a long time showed shrinkage of interfacial defects, which resulted in the increase of bonding strength. On the other hand, it became clear that relaxation of residual stress as well as bulk softening is a contributing factor for the increase in bonding strength for the specimens held at high temperature for a short time.