Joining Si3N4 ceramic to Invar using Mo mesh and Cu foil interlayer

Si3N4/Invar joints with Mo mesh and Cu foil as interlayers, individually and together, were vacuum brazed using Ag27.5Cu4.5Ti active filler at 1153 K for 10 min with following configurations: Si3N4/Ag26.7Cu4.5Ti + Mo/ Invar, and Si3N4/Ag26.7Cu4.5Ti + Mo/Cu/Ag-Cu/Invar. The correlation between the microstructure of the brazing seam and shear strength of the joints are investigated. Ti segregated at Si3N4/filler interface and metallurgical bonding is established by formation of TiN and Ti5Si3 reaction products. Vickers microharndess profiles unveiled varying degrees of hardness across the brazing seam, resembling the layered structure. Indi-vidually introducing Mo mesh as interlayer suppressed the Fe2Ti and Ni3Ti intermetallic compounds (IMC) within the brazing seam, resulting in shear strength of 191.7 MPa. Hybrid combination of Mo mesh with Cu foil as interlayers, yielded 235.5 MPa shear strength in brazed Si3N4/Invar joints. This improvement is attributed to simultaneous favorable effects of Mo such as reduced residual stress near the Si3N4/filler interface and Cu, which prevents Fe2Ti and Ni3Ti IMC in the brazing seam, thereby enhancing the plastic flow.