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

Abstract

Abstract SiO 2 -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 SiO 2 was not reacted during brazing while h-BN had strong tendency to react with Ti to formation a fine-grain layer adjacent to SiO 2 -BN ceramic. The composite TiN–TiB 2 fine-grain layer with the thickness of 100–150 nm was the key factor in achieving a good bond between SiO 2 -BN ceramic and Invar. Invar alloy dissolved into the molten filler and reacted with Ti to form Fe 2 Ti and Ni 3 Ti, which dispersed in Ag- and Cu-based solid solution. The shear strength of the joint decreases with the increase of Fe 2 Ti and Ni 3 Ti brittle compounds. The maximum shear strength reached 32 MPa when the joint brazed at 1153 K for 10 min. Cracks primarily propagated in the SiO 2 -BN ceramic and partially along the reaction layer.