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.%.