Abstract
Transparent sapphire and magnesium aluminum spinel (MgAl2O4) ceramic was first brazed using La2O3-SiO2-B2O3-Nb2O5 (LSBN) or La2O3-SiO2-B2O3-Nb2O5-MgO (LSBNM) glass filler. The Al2O3 layer was formed at MgAl2O4/LSBN interface or sapphire/LSBNM interface, which caused the decrease of light transmission of joints. To avoid the formation of this interface layer, sapphire/LSBN/LSBNM/MgAl2O4 joints with double glass interlayers were fabricated by using a two-step joining method consisting of high-temperature coating and low-temperature bonding. After the first step of high-temperature coating, no interfacial layer was observed in sapphire/LSBN glass and MgAl2O4/LSBNM glass samples. During the bonding process, low bonding temperature (750 °C) resulted in cracks and unbonding, while high bonding temperature (950 °C) caused the crystallization of glass interlayers. However, when the bonding temperature was 850 °C, the in-line transmission and shear strength of the sapphire/MgAl2O4 joints reached 78.3% and 52 MPa, respectively.
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