Interfacial microstructure and sealing mechanism of Kovar alloy joint sealed with high-strength glass-ceramics

Traditional sealing glass has limitations in extreme environments due to its low high-temperature electrical insulation, poor chemical stability, and inherent brittleness. In this study, we suggest the use of B₂O₃-Al₂O₃-SiO₂ (BAS) glass-ceramics instead of conventional glass, coupled with pre-oxidized metals, to construct superior micro-interfacial structures. We developed a series of sealing glass-ceramics by adjusting the Al₂O₃ content in the parent glass and managing the ratio of crystalline to residual glass phases to achieve compatibility with Kovar alloy. Our findings indicate that Al₂O₃ improves the coefficient of thermal expansion, alkali resistance, bending strength (up to 174 MPa), Vickers hardness (6.60 GPa), and high-temperature resistivity. The seals between Glass-Ceramics and Kovar alloy reached a maximum strength of 7.49 MPa under optimal parameters (pre-oxidation at 950 °C, sealing at 985 °C for 30 min). Interface analysis identified five zones, and the sealing mechanism was elucidated. The BAS glass-ceramics prove to be exceptional high-temperature sealing materials. This study offers mechanistic insights into metal-to-glass-ceramics seals for special equipment.