Microstructural evolution during reactive brazing of alumina to Inconel 600 using Ag-based alloy

A metal-ceramic bonding process was developed to produce vacuum tight alumina-Inconel 600 joints using an Ag-based active metal brazing alloy that can withstand continuous operating temperature up to 560 °C. The microstructure and microchemistry of the braze zone was examined using extensive microanalysis of the constituent phases and a mechanism for the interfacial reactions responsible for the bonding is proposed. Prolonged heat treatment at 400 and 560 °C under simulated in-service conditions revealed that the microstructure of braze zone of the joints was stable and maintained leak-tightness and strength. The bond strength of the interface was high enough to cause failure in the alumina side of the joints. Failure of the joints was caused by initiation of crack on the surface of alumina as a result of high tensile residual stress adjacent to the metal-ceramic interface.