Microstructure and mechanical response of the SiO_2f/SiO₂ composite and Invar alloy joints brazed with an AgCuTi alloy

The SiO_2f/SiO₂ composite and the Invar alloy were brazed at 860 °C from 5 min to 25 min using an AgCuTi alloy. Scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) was employed to examine the elemental distribution in the joint. X-ray diffraction (XRD) and transmission electron microscopy (TEM) was selected to accurately identify the species, morphologies and crystal structures of the reaction products. The effect of the holding time on the interfacial microstructure evolution of the joint was studied in detail. The shear strength of the joints and the fracture morphologies were closely related to the thickness of the whole reaction layer, as well as the thickness ratio of the Ti₅Si₃ + TiO₂ layer to the Cu_xTi_6-xO layer. The maximum shear strength was 26 MPa obtained at 860 °C for 10 min. Finally, the formation of the reaction products in the joint was analyzed by thermodynamic calculations. A brazing mechanism was proposed based on the experimental results.