Wetting and strength issues at Al/α–alumina interfaces

The wetting behavior and strength at aluminum/alumina interfaces is an active subject of research. Al/alumina applications include ceramic-metal composites and several applications for electronic industries. In this paper the interface strength and microstructure of Al/α-alumina was investigated. We discovered that, in a solid-state joining, the strength of the joint increases with increasing joining temperature, whereas, in a liquid-state joining, the strength of the joint gradually decreases with increasing temperature due to the formation of unbonded areas. The strength, σb, is expressed by the following equation as a function of unbonded area, A: σb=2.69 A+116 (70%⩽A⩽100%). The highest strength reached 400 MPa when the interface was formed around the melting temperature of aluminum. An aluminum layer close to the interface became a single crystal when it was bonded to a sapphire. The following crystallographic orientation relationship was established:1̄11Al//001α-Al2O3,<110>Al//<100>α-Al2O3Amorphous alumina islands were formed at the interface. In the amorphous alumina, γ-alumina nanocrystals grew from the sapphire, with the same orientation relationship to sapphire as above.