Effects of Cu interlayers on the microstructure and mechanical properties of Al2O3/AgCuTi/Kovar brazed joints

Al₂O₃ ceramic and Kovar alloy brazed joints were achieved using three types of Ag-based interlayers: a AgCuTi foil, a AgCuTi/Cu foil/AgCuTi multi-interlayer and a AgCuTi/Cu foam/AgCuTi multi-interlayer. The effects of the addition of Cu interlayers on the interfacial microstructure and mechanical properties of Al₂O₃/AgCuTi/Kovar brazed joints were investigated. When Kovar alloy and Al₂O₃ ceramic were brazed with 50 μm Cu foil at 900°C for 10 minutes, the Cu foil was completely dissolved in the liquid filler. A nearly continuous Cu layer remained in the joint when the thickness of the Cu foil reached 100 μm under the same brazing conditions. With the increase in Cu foil thickness, the thickness of Ti–O compounds + Ti₃Cu₃O reaction layer formed nearby the Al₂O₃ ceramic first increased and then remained the same. The Al₂O₃/Kovar joints brazed with 100 μm Cu foil at 900°C for 10 minutes showed a maximum shear strength of 138 MPa. A low brazing temperature was beneficial to maintain the original structure of the Cu foam. Furthermore, when the joints were brazed at 880°C for 10 minutes, the average shear strength of the Al₂O₃/AgCuTi/Cu foam/AgCuTi/Kovar joints was 140 MPa, which was 30 MPa higher than that of a single AgCuTi interlayer.