In-situ strengthening mechanism of glass brazing Al₂O₃ ceramics joints

In view of the problems of poor machinability, difficult preparation of complex structure and large-size components of Al₂O₃ ceramics, 48.5%SiO₂-48.5%B₂O₃-3%Na₂O borosilicate glass was used to obtain reliable bonding of Al₂O₃ ceramic which not only had excellent mechanical properties, but also can form an in-situ reinforced phase with Al₂O₃ ceramics. It was shown that during the brazing process, as Al₂O₃ ceramics diffusing and dissolving into the glass braze, SiO₂-B₂O₃-Na₂O glass transformed to SiO₂-B₂O₃-Al₂O₃-Na₂O glass in the seam. The integration of Al₂O₃ strengthened the glass matrix. Furthermore, a large number of dispersed aluminum borate whiskers were in-situ generated not only inside the glass matrix but also at the interface between glass braze and Al₂O₃ ceramics, forming the in-situ aluminum borate whiskers reinforced composite Al₂O₃/Al₂O₃ joints brazed by borosilicate glass. 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 interface, realizing a high-strength and high-reliability connection of Al₂O₃ ceramics. When temperature is 1 250 ℃ and time is 60 min, the joint strength reached the highest value of 136 MPa.