Fabrication of sapphire/MgAl2O4/sapphire laminated transparent composite by brazing with BaO-B2O3-SiO2 glass filler

For improving the mechanical properties of MgAl2O4 ceramic and maintaining its wide band transparency, the sapphire/MgAl2O4/sapphire laminated transparent composites with thin sapphire layers were fabricated by brazing with BaO-B2O3-SiO2 (BBS) glass filler. The BBS glass filler had an appropriate CTE (coefficient of thermal expansion) value and good wettability on the surface of sapphire and MgAl2O4 ceramics. Joining experiments were first carried out to optimize the preparation process parameters of laminated composites. The results indicated that high bonding temperature promoted mutual dissolution and diffusion of BBS glass and MgAl2O4 ceramic, but led to the intergranular infiltration of glass filler and the formation of pores due to volatilization of B2O3. When the bonding temperature was 1000 °C, the sapphire/MgAl2O4 joints with the best transparency and acceptable shear strength could be obtained. On this basis, the laminated composites with 0.15 mm thick sapphire layers were fabricated by brazing using BBS glass at 1000 °C. The flexural strength of the laminated composite reached 320 ± 10 MPa, which was higher than that of MgAl2O4 (195 ± 15 MPa). The in-line transmittance of laminated composite was 80.9% at 1000 nm, which was slightly lower than that of MgAl2O4 (82.2%).