Microstructure and mechanical properties of ZrB₂-SiC ceramic composite brazed joint

The ZrB₂-SiC ceramic matrix composites were joined by vacuum brazing with BNi₂ filler metal. SEM,EDS and XRD were used to analyze the interface microstructure and properties. The optimized brazing parameters were 1 160℃ of brazing temperature and 20 min of holding time. The experimental results show that the interface products were mainly δ-Ni₂Si,β₁-Ni₃Si,ZrB₂+C,Ni(s,s) and Cr_xB_yC_z phases. With the increase of brazing temperature and holding time, the shear strength of the joint increased first and then decreased. The maximum shear strength of the joint brazed at 1 200℃ for 20 min reached 121 MPa. The effect of brazing temperature and holding time on the joint fracture mechanism was similar. When the holding time was short,cracks mainly occurred at Ni(s,s) in the seam,and then propagated to the Ni diffusion layer. When the holding time was suitable,the fracture mainly occurred in the Ni diffusion layer. When the holding time increased further, cracks mainly initiated in the Ni(s,s) with some β₁-Ni₃Si and later developed to the Ni diffusion layer.