Joining alumina using an alumina/metal composite

Alumina/alumina (Al2O3/Al2O3) joints and alumina/aluminium metal–matrix composite (Al2O3/Al–MMC) joints were fabricated using an Al2O3–Al composite as an interlayer. The Al2O3/Al2O3 joining procedures involved the sintering of silica or silicate glass on the surface of the Al2O3, followed by the reactive penetration of liquid aluminium into the sintered glass to form an Al2O3–Al composite interlayer between the two Al2O3 pieces. To join Al2O3 to Al–MMC, after the fabrication of the Al2O3–Al composite layer on the surface of Al2O3 using the combination of sintering and reactive penetration, Al2O3/composite/MMC joints were fabricated by using diffusion bonding between the Al2O3–Al composite layer and the MMC. The microstructures, phase composition and mechanical properties of the joints were examined using scanning electron microscopy (SEM), XRD analysis and shear testing, respectively. Experimental results showed that the high porosity in the sintered glass layer led to the formation of a porous Al2O3–Al composite layer between two Al2O3 pieces. The addition of cordierite (2MgO·2Al2O3·5SiO2) to the pure silica lowered the melting point of the glass and led to the formation of a dense glass layer at the surface of the Al2O3. Consequently, a dense composite layer was produced. Stronger joints were fabricated with shear strengths of the Al2O3/Al2O3 and Al-MMC/Al2O3 joints of 105.2 and 47.6 MPa respectively.