Wetting and sealing of interface between 7056 Glass and Kovar alloy

This study examines the wetting and sealing of Kovar alloy with 7056 Glass. First, the Kovar alloy underwent pre-oxidization treatment at three different temperatures (700, 800 and 900 °C) and for seven different isothermal holding periods (0, 3, 5, 10, 15, 30 and 60 min), producing oxide layers of different thickness on the surface of the alloy. Then the wetting experiment was conducted at 925 °C for 15 min to observe the wettability of 7056 Glass on the underlying Kovar alloy discs. Finally, Kovar alloy and 7056 Glass were joined at thermal treatment temperature of 825–1000 °C with isothermal holding for 15 min at every interval of 25 °C. The wetting phenomenon and interface structure were observed under optical microscope and elemental analysis was also conducted on the glass-to-metal junction using an electron probe micro-analyzer. Experimental results reveal that Kovar alloy pre-oxidized at 700 °C and held isothermally for 5–15 min would have a denser and more compact oxide layer of 4–7 μm thick showing good adherence. Kovar alloy pre-oxidized at 700 °C and 10 min isothermal holding and heated in furnace filled with nitrogen only would obtain good wettability. Finally, thermal treatment temperature of 900 °C and 15 min isothermal holding resulted in a bigger surface area of the reaction layer and high-quality glass-to-metal junction.