Brazing SiO₂-BN diphase ceramic with Nb by using multilayer Ti-Ni composite foils

The multilayer Ti and Ni foils were designed to braze SiO₂-BN diphase ceramic with Nb at 1140 °C for 5min. The interfacial microstructure was examined using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD) methods, respectively. Experimental results and thermodynamical calculations showed that the interfacial microstructures between Nb and SiO₂-BN ceramic were (βTi,Nb)-TiNi eutectic structure/TiNi + TiNi₃/TiN + Ti₃O₅ + TiB₂ + Ti₅Si₃. The effects of the Ti content in the Ti-Ni braze alloy on the microstructures of the joints were investigated. With the increase of the Ti content, less Ni₃Nb formed in the joint and TiNi₃ phase successfully turned into TiNi and Ti₂Ni. The effects of the Ti content in the Ti-Ni braze alloy on the shear strength of the joints showed that the optimum thickness of the TiN + Ti₃O₅ + TiB₂ + Ti₅Si₃ reaction area was about 13 μm and the maximum shear strength of 52 MPa was achieved when the Ti content was 45 wt.%.