Microstructure and mechanical properties of Si₃N₄/Cu AMB joints

The active metal brazed joints of Si₃N₄ and Cu were obtained by using Ag-Cu-In-Ti brazing filler at a brazing temperature of 780 °C. The interfacial microstructure of the joint and its formation mechanism were investigated, and the effect of holding time on the interfacial microstructure and mechanical properties of the joint was analyzed. The results have shown that during brazing, the Ti element reacts with Si₃N₄ to form a 170 nm-thick nanocrystalline TiN and a Ti₅Si₃ layer with a wavy profile. In the brazing seam, the residual Ti atoms after the reaction integrate with two brittle compounds, Cu₂InTi and Cu₄Ti. In addition, a very small amount of Cu₃Ti₂ and CuTi phases occurs. By regulating the reaction process at the Si₃N₄ ceramic-side interface, the holding time controls the morphology of the Ti₅Si₃ reaction products, as well as the content of brittle Cu₂InTi and Cu₄Ti compounds in the brazing seam, which determines the shear strength of the brazing joints. With the extension of the holding time, the interfacial reaction becomes more sufficient, and the amount of brittle intermetallic compounds in the brazing seam decreases. When the holding time is 20 min, the shear strength of the joints reaches the highest, with a value of 309 MPa. The fracture occurs at the interfacial reaction bilayer close to the Si₃N₄ ceramic, among which the Ti₅Si₃ is weaker.