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

Infrared brazing of Al2O3 and alloy 42 using a silver-base active braze all oy was investigated at 900 degrees C for 0 to 300 seconds, with a heating r ate of 3000 degrees C/min. Experimental results show that Ti-3(Cu, Al)(3)O 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-l ayer structure is observed at the reaction interface brazed at 900 degrees C for 5 seconds. The reaction layer close to the alumina contains large amo unts 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 heati ng rate of 10 degrees C/min demonstrate that the wetting angle rapidly decr eases within the first 150 seconds, especially 0 to 80 seconds, and eventua lly stabilizes after 600 seconds.