Microstructure and strength of interface between pure aluminum and α-alumina

Abstract

The interface strength and microstructure of α-alumina/pure aluminum were evaluated. In a solid-state joining, the strength of the joint increases with increasing joining temperature. In a liquid state joining, the strength gradually decreases due to the formation of an unjoined area. The strength, σb, is expressed by the following equation as a function of the unjoined area, A,: σb=2.22A+143 (70%≦A≦100%). The highest strength reached 400 MPa when the interface is formed at around the melting temperature of aluminum. An aluminum layer becomes a single crystal when it is joined to a sapphire. The following crystallographic orientation relationship is established: (111)Al//(001)α-Al2O3,〈110〉 Al//〈100〉α-Al2O3 Amorphous alumina islands are formed at the interface. In the amorphous alumina, spinel nano crystals grow from the sapphire and they have the same orientation relationship with sapphire as above.