Competitive correlation between the interface layers determines the shear strength in Kovar/AgCuTi/Si3N4 joints

Abstract

As a promising high-thermal-conductivity ceramics, the direct bonding of Si₃N₄ with metals remains challenging. Here, we employed active metal brazing of Si₃N₄ ceramics and Kovar alloys using AgCuTi metal filler, and found that the shear strength in the prepared Kovar/AgCuTi/Si₃N₄ joints depends on the competitive correlation between the interface layers. The competitive consumption for active element Ti by Kovar/AgCuTi interfacial reactions reduced AgCuTi/Si₃N₄ 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 Ti₅Si₃ was the primary cause of failure. Density functional theory (DFT) revealed that Ag (111)/Fe₂Ti (001) interface had higher ideal work of adhesion (W_ad) than Ag (111)/Ti₅Si₃ (001) interface, confirming the importance of AgCuTi/Si₃N₄ interface layer. Ultimately, by adjusting interface reaction layer thickness, the joints reached a high shear strength of 154.3 MPa.