Joining of alumina with a porous alumina interlayer

In the joining of structural ceramics, a porous interlayer is generally believed to deteriorate the mechanical properties of the joint. This paper, however, shows that a porous interlayer can sustain high adhesion strength when cavities or interfacial cracks are eliminated. The characteristic of the new slurry approach, described in this work, is that a pure alumina slurry interlayer is dried between two adjoining dense alumina plates and sintered with a negligible external pressure to form the porous interlayer. The effect of slurry concentration was studied to optimize the microstructure of interlayer. By controlling the interlayer microstructure and nature of the flaws, it was possible to fabricate high-strength bonds. The new slurry approach opens up the possibility of pure diffusion bonding which requires neither high pressure during heat treatments nor flat surfaces.