Microstructure and properties of brazed joints of C/C and TC4 with foamed Cu/AgCuTi composite interlayer

To address the issues of residual stress concentration and excessive brittle phase formation at the joints of C/C composites and TC4 alloy during brazing, a foamed Cu/AgCuTi composite interlayer for heterogeneous bonding was employed. The effects of brazing temperatures (860 ~ 920 °C) on interfacial microstructures, shear strength, and fracture morphology of the joints were systematically investigated. The results show that all joints achieve reliable metallurgical bonding, with a typical interfacial structure of TC4/Ti-based solid solution + TiCu/Ag-based solid solution + Cu-based solid solution + TiCu₂/TiC/C/C composites. As the brazing temperature increases, the width of the brazing seam gradually decreases, while the phase composition and distribution patterns remain consistent. Compared to conventional AgCuTi brazing alloy, the foamed Cu/AgCuTi composite interlayer significantly enhances the Cu-based solid solution content in the seam, effectively reducing residual stress accumulation during cooling and suppressing brittle compound formation. The shear strength of the joints exhibits an initial increase followed by a decrease with rising temperature, peaking at 29.2 MPa at 880 °C. Fracture analysis reveals a correlation between fracture characteristics and interfacial evolution, demonstrating the positive impact of the composite interlayer design on enhancing the mechanical properties of the joints.