INTERLAYER MICROSTRUCTURE AND BONDING BEHAVIOR OF ULTRASONIC-WELDED ALUMINUM-OXIDE ALUMINUM JOINTS

The microstructure and composition of interlayers in ultrasonically we lded Al/Al2O3 compounds are investigated by high voltage and high reso lution transmission electron microscopy including X-ray microanalysis. The joining is mainly effected via a 2 to 20 nm thin amorphous interl ayer of Al and O, which probably is an oxide with an excess of metal. Oxygen has diffused from alumina toward the metal, with the interlayer probably being a residue of the former oxide layer on the metal or a reaction product caused by the welding process. Numerous crystal defec ts, unbonded porous regions and microcracks in the ceramic owing to fr iction and thermal mismatch are observed as well as indications of loc al transient melting. Different orientations and pre-treatments do not lead to major changes in the observed interlayer defect structure whi ch possibly governs the quality of the welding procedure and thus the interlayer shear strength.