Microstructural evolution at the bonding interface during the early-stage infrared active brazing of alumina

Abstract

Infrared brazing of Al₂O₃ and alloy 42 using a silver-base active braze alloy was investigated at 900 °C for 0 to 300 seconds, with a heating rate of 3000 °C/min. Experimental results show that Ti₃(Cu, Al)₃O intermetallic with various amounts of Al is observed in the reaction layer and plays an important role in the early stage of reactive wetting. A two-layer structure is observed at the reaction interface brazed at 900 °C for 5 seconds. The reaction layer close to the alumina contains large amounts of Al, so the mass balance of the system is maintained. The growth of the reaction layer is not rate controlled by diffusion within the first 120 seconds. After 120 seconds, the rate controlling mechanism of the reaction layer becomes the diffusion control, satisfying the parabolic law. Dynamic wetting angle measurements using a traditional vacuum furnace at the heating rate of 10 °C/min demonstrate that the wetting angle rapidly decreases within the first 150 seconds, especially 0 to 80 seconds, and eventually stabilizes after 600 seconds.