Interfacial microstructure and mechanical property of SiO2-BN ceramics and Invar joint brazed with Ag–Cu–Ti active filler metal

Highlights: ► The diffusion of Fe and Ni from Invar has great influence on joint microstructure. ► Shear strength depends heavily on Ni3Ti and Fe2Ti brittle compounds. ► Formation mechanism of the composite TiN–TiB2 fine-grain layer was discussed. ► TiN–TiB2 fine-grain layer was the key factor in achieving a good bonding. - Abstract: SiO2-BN ceramics and Invar alloy were jointed by active brazing using Ag–21Cu–4.5Ti (wt.%) filler at 1113–1173 K for 5–30 min. Scanning and transmission electron microscopy studies revealed that the amorphous SiO2 was not reacted during brazing while h-BN had strong tendency to react with Ti to formation a fine-grain layer adjacent to SiO2-BN ceramic. The composite TiN–TiB2 fine-grain layer with the thickness of 100–150 nm was the key factor in achieving a good bond between SiO2-BN ceramic and Invar. Invar alloy dissolved into the molten filler and reacted with Ti to form Fe2Ti and Ni3Ti, which dispersed in Ag- and Cu-based solid solution. The shear strength of the joint decreases with the increase of Fe2Ti and Ni3Ti brittle compounds. The maximum shear strength reached 32 MPa when the joint brazed at 1153 K for 10 min. Cracks primarily propagated in the SiO2-BN ceramic and partially along the reaction layer.