Active Brazing Alloys
Active brazing alloys (ABAs) are specially alloyed metals that promote wetting on ceramics. Active alloys allow for the direct joining of metals to ceramics by forming an intermediate layer on the ceramic during the braze process thus allowing for the braze alloy to wet to the intermediate layer.
ABA’s should be brazed in vacuum or argon. If brazed in argon, the vapor pressure of elements such as silver should be taken into consideration when programing the peak temperature. ABA’s are best suited for furnaces. Induction can cause uneven heating which leads to the cracking of ceramic components. Rapid cool down rates should also be avoided when ceramic is brazed to metal. The fast contraction of metal can put stresses on the ceramic which lead to cracking or residual stress on the braze joint at ambient temperatures.
The soak time at temperature is often extended for ABA’s to allow the active agent to react with the surface of the ceramic. ABA’s cannot be brazed in atmosphere with flux or under nitrogen.