Active metal brazing of SiO2-BN ceramic and Ti plate with Ag-Cu-Ti + BN composite filler

SiO2-BN ceramic and Ti plate were joined by active brazing in vacuum with Ag-Cu-Ti + BN composite filler. The effect of BN content, brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated. The results showed that a continuous TiN-TiB2 reaction layer formed adjacent to the SiO2-BN ceramic, whose thickness played a key role in the bonding properties. Four Ti-Cu compound layers, Ti2Cu, Ti3Cu4, TiCu2 and TiCu4, were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag. The central part of the joint was composed of Ag matrix, over which some fine-grains distributed. The added BN particles reacted with Ti in the liquid filler to form fine TiB whiskers and TiN particles with low coefficients of thermal expansion (CTE), leading to the reduction of detrimental residual stress in the joint, and thus improving the joint strength. The maximum shear strength of 31 MPa was obtained when 3 wt% BN was added in the composite filler, which was 158% higher than that brazed with single Ag-Cu-Ti filler metal. The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content, brazing temperature and holding time. Based on the correlation between the microstructural evolution and brazing parameters, the bonding mechanism of SiO2-BN and Ti was discussed.