Interfacial microstructure and mechanical property of SiO_2-BN ceramics and Invar joint brazed with Ag-Cu-Ti active filler metal

摘要

SiO_2-BN ceramics and Invar alloy were jointed by active brazing using Ag-21Cu-4.5Ti (wt.%) filler at 1113-1173K 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-TiB2 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_2Ti and Ni_3Ti, which dispersed in Ag- and Cu-based solid solution. The shear strength of the joint decreases with the increase of Fe_2Ti and Ni_3Ti 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.