The microstructural evolution and formation mechanism in Si3N4/AgCuTi/Kovar braze joints

The braze joints of Si3N4-Kovar using AgCuTi braze alloys are investigated systematically with the brazing temperatures between 860 °C and 950 °C for 2–30min. The correlation between the joint strength and the microstructures of the braze joints is discussed. These results show that the reaction layer plays an important role in interface bonding. Growth of the reaction layer is a reaction-diffusion process, which mainly depends on the diffusion of Ti. The diffusion activation energy (Q) is estimated as 170.9–248.7 kJ/mol in this system, which may provide data support for Si3N4/metal braze joints. As the holding time is further prolonged (in the range of 10–30min), intermetallic compounds (IMCs) forms in the braze seam, which will prevent Ag solid solution from alleviating interfacial thermal stress. With the increasing of the brazing temperature, the residual thermal stresses increases. As a results, larger residual thermal stress is produced in the braze joints at higher braze temperature, which result in a weaker bonding. •The braze joints of Si3N4-Kovar using AgCuTi are investigated systematically.•An interfacial reaction layer plays an important role in interface bonding of Si3N4-Kovar.•Growth of the reaction layer is a reaction-diffusion process.•Ag(s, s) plays an important role in relieving residual thermal stress.•The fracture mechanism of the joint is further explored.