Microstructure Controlling, Properties, and Thermodynamic Analysis of SiC Joints Brazed with Ni-Ti Fillers

Silicon carbide (SiC) ceramics were brazed with Ni-Ti fillers at 1350 °C for 10 min. The experimental results show that with the increase in Ti content in the fillers, the interface layer composed of Ni₂Si, Ni₃Si₂, graphite, and TiC becomes thinner due to the inhibition of the Ti/SiC reaction on the Ni/SiC reaction. When Ni-45Ti filler is used, TiC becomes the only phase of the interface layer in the brazing seam. The elimination of graphite improves the mechanical property of the joints. The shear strength of the SiC joints brazed by Ni-15Ti, Ni-30Ti, and Ni-45Ti fillers is 33 MPa, 92 MPa, and 125 MPa, respectively. From the point of thermodynamics, the calculated component point of the Ni/SiC reaction transition to the Ti/SiC reaction is x_Ti = 31 at.%. When the Ti content is higher than 31 at.%, the ΔG_Ni/SiC > ΔG_Ti/SiC, and TiC will be preferentially generated at the interface. Therefore, the Ni/SiC reaction is inhibited and the harmful graphite is eliminated.