Pressure-less joining SiCf/SiC tube and Kovar alloy with AgCuInTi filler: Interfacial reactions and mechanical properties

Abstract

The brazing of tube-bar structures is more difficult than that of traditional plate-plate structures, owing to the absence of pressure on the interface. In this study, AgCuInTi filler was employed to join SiC_f/SiC tube and Kovar alloy bar and the joining can be completed at a significantly lower temperature of 780 °C, benefiting from the addition of In. Moreover, the lower temperature not only hindered the formation of Fe₂Si and Ni₂Si at the ceramic interface, but also avoided the appearance of the Fe₂Ti phase in the joint. The typical microstructure of the joint was SiC_f/SiC-(TiC + Ti₅Si₃) layer + (Ag, In) (s, s) + Cu (s, s) + Cu₇In₃+ Ni₃Ti-Kovar. The finite element analysis indicated that lower brazing temperature can also reduce the level of residual stress compared to that of AgCuTi filler, which contributes to the maximum shear strength of 86.1 MPa despite the press-less joining. The fracture path originated from the SiC fibers, then passed through the interfacial reaction layer, and finally extended into the brazing seam.