Review of reactive air brazing: fundamental, progress, and perspective

Reactive air brazing (RAB) has been widely applied in fabricating solid oxide fuel cell stacks, gas separators, sensors, and other fields due to the joint good oxidation resistance. Nevertheless, a methodical analysis of fundamental principles, development process, and application scope has yet to be reported since RAB was proposed in 2000. Although various braze systems have been developed, a comprehensive comparison and classification are still absent, making it difficult to guide the selection of RAB braze. Besides, this technique faces several intractable issues, such as excessive interfacial reactions, large thermal mismatch, etc., seriously restricting the RAB application. Hence this review elucidates the basic information, braze systems, existing issues, and corresponding solutions of RAB. The joining mechanism, development history, and application fields are explicitly introduced. Reported braze systems are analyzed in-depth and divided into three categories according to reactivity. Further, we outline four issues of RAB: excessive interfacial reaction, excessive thermal expansion coefficient of braze, limited aging performance, and high-temperature softening of braze, and discuss the corresponding solutions. Finally, our review proposed several potential improvements and possible future research trends in the RAB technique, aiming to guide the future development of RAB and offer new insights to broaden its application range.