Joining of Al₂O₃ by epitaxial growth of aluminum borate whiskers for higherature applications

Alumina ceramics were directly bonded for higherature applications by epitaxial growth of aluminum borate whiskers in air. The Al₂O₃/whisker/Al₂O₃ joints were characterized via scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The microstructural observations showed that the Al₁₈B₄O₃₃ whiskers along the [001] crystallographic direction grew across the seam and thereby achieving the joining of alumina substrates. Both of whiskers diameter and density of joints increased with the increase of bonding temperatures. Three-point bending results showed that the maximum strength of the joints tested at 800°C was 27 MPa. The possible mechanism of the bonding process was discussed as well.