In-situ strengthening of Al₂O₃ ceramic glass brazing joint and its mechanism

In view of the problems of poor machinability, difficult preparation of complex structure and large-size components of Al₂O₃ ceramics, 48.5SiO₂-48.5B₂O₃-3Na₂O(mol.%) borosilicate glass was used to obtain reliable bonding of Al₂O₃ ceramic which not only has excellent mechanical properties, but also can form a reinforced phase with Al₂O₃ ceramics in situ. The results show that during the brazing connection, Al₂O₃ ceramics diffuse and dissolve into the glass solder, and SiO₂-B₂O₃-Na₂O glass transformed to SiO₂-B₂O₃-Al₂O₃-Na₂O glass in the weld zone, and the integration of Al₂O₃ improves the mechanical strength of the glass matrix. Furthermore, a large number of dispersed aluminum borate whiskers were generated in situ inside the glass matrix and at the interface between glass solder and Al₂O₃ ceramics, forming an aluminum borate whisker reinforced borosilicate glass composite joint of Al₂O₃ ceramics, and the whiskers not only further strengthened the glass matrix through pull-out effect, crack deflection, crack bridging, absorption effect, etc., but also played the role of nailing and suturing at the connection interface, realizing the high-strength and high-reliability connection of Al₂O₃ ceramics. When temperature is 1250 ℃ and time is 60 min, the joint strength reached the highest value of 136 Mpa.