Microstructure and mechanical properties of the SiC/Nb joint brazed using AgCuTi+B4C composite filler metal

Abstract

The residual stress is considered to be the driving force for the failure of ceramic/metal brazing joint. In this paper, the residual stress in a SiC/Nb joint is alleviated by using AgCuTi+B4C composite brazing filler. SEM, EDS and XRD are applied to characterised the microstructure of the joint, which is determined to be SiC/Ti3SiC2/Ag(s,s)+Cu(s,s)+TiB+TiC/TiCu+ Nb(s,s)/Nb. The effects of the B4C strengthening phase mass fraction and the brazing temperature on the microstructure and the mechanical properties of the joint are investigated. It is found that the reaction products between B4C and the brazing filler (TiB whisker and TiC particles) uniformly distribute inside the joint if the mass fraction of the B4C is not higher than 1.5 wt% and when the amount of B4C reaches 2 wt%, the reaction products begin to agglomerate. With the rising of the brazing temperature, the thickness of the Ti3SiC2 reaction layer next to the ceramic increases and when the brazing temperature reaches 910 °C, another reaction layer of Ti5Si3 can be found adjacent to the Ti3SiC2 reaction layer. The strength of the joint first increases and then decreases with the increase of both the strengthening phase and the brazing temperature. The highest shear strength of the joint reaches 98 MPa when the joint is achieved at 890 °C using AgCuTi+1.5 wt%B4C brazing filler.