Impact of ZnO content in BAS glass–ceramics and pre-oxidation temperature on Kovar alloys to their sealing strength

This work studied the effect of Si/Zn ratio on the structure of B₂O₃–Al₂O₃–SiO₂ (BAS) parent glass and the microstructure, properties of the resulting glass-ceramics after heat treatment. Additionally, the effects of different pre-oxidation temperature of Kovar alloys and sealing temperature on the shear strength of these sealed glass–ceramics-to-Kovar samples were studied. First, the parent glass precipitated three kinds of crystals Al_0.52Zr_0.48O_1.74 (PDF#53-0294), ZrO₂ (PDF#37-1484), and ZnAl₂O₄ (PDF#05-0669) in BAS glass–ceramics. The coefficient of thermal expansion of glass–ceramics increased from 48.17 × 10⁻⁷ to 54.92 × 10⁻⁷°C⁻¹ with the gradual increase of ZnO content. With an optimizing pre-oxidized temperature of Kovar at 950°C, a champion sample with the highest sealing strength of 6.086 MPa was achieved when BAS glass–ceramics sealed to Kovar at 1000°C for 30 min. Moreover, the sealing interface was observed to consist of four distinct regions: the matrix alloy, the alloy iron-deficiency area, the iron-rich glass–ceramics, and the matrix glass–ceramics.