Competitive correlation between the interface layers determines the shear strength in Kovar/AgCuTi/Si 3 N 4 joints

As a promising high‐thermal‐conductivity ceramics, the direct bonding of Si 3 N 4 with metals remains challenging. Here, we employed active metal brazing of Si 3 N 4 ceramics and Kovar alloys using AgCuTi metal filler, and found that the shear strength in the prepared Kovar/AgCuTi/Si 3 N 4 joints depends on the competitive correlation between the interface layers. The competitive consumption for active element Ti by Kovar/AgCuTi interfacial reactions reduced AgCuTi/Si 3 N 4 interface layer thickness and deteriorated final shear strength, even when using a high‐Ti‐content filler. Surface analysis indicated that interfacial fracture between Ag‐based solid solution and Ti 5 Si 3 was the primary cause of failure. Density functional theory (DFT) revealed that Ag (111)/Fe 2 Ti (001) interface had higher ideal work of adhesion ( W ad ) than Ag (111)/Ti 5 Si 3 (001) interface, confirming the importance of AgCuTi/Si 3 N 4 interface layer. Ultimately, by adjusting interface reaction layer thickness, the joints reached a high shear strength of 154.3 MPa.