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

Abstract This work studied the effect of Si/Zn ratio on the structure of B 2 O 3 –Al 2 O 3 –SiO 2 (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 0.52 Zr 0.48 O 1.74 (PDF#53‐0294), ZrO 2 (PDF#37‐1484), and ZnAl 2 O 4 (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.