Interfacial microstructure and mechanical properties of the vacuum brazed C/SiC composite and Nb joints

In the present study, vacuum brazing was adopted to join carbon fiber reinforced silicon carbide (C/SiC) composite and Nb using Ti-Ni composite foils. The interfacial microstructure as well as mechanical properties was investigated, and the contact-reaction mechanism was analyzed. The results show that, (Ti, Nb)C reaction layer, (Ti, Nb)2Ni and Ti-Ni-Nb-Si compounds, and TiNi-(Nb, Ti) eutectic form in braze seam. Ti-Ni composite foils turn into liquid eutectic alloy by two stages. Firstly, Ti and Ni foils react to fabricate TiNi alloy. Secondly, the pseudo-binary eutectic reaction of TiNi and Nb substrate begins to form the liquid eutectic alloy. The maximum shear strengths of the brazed joints reach 192 MPa, 155 MPa, 115 MPa and 82  MPa at room temperature, 600 °C, 800 MPa and 1000 °C, respectively. To enhance the mechanical properties of the joints, laser drilling holes on C/SiC composite prior to brazing was proposed. Because the infiltration of filler alloy into holes can increase the load bearing capacity and decrease the residual stress of the joint, the shear strengths of laser-drilled joints are significantly improved to 259 MPa, 186 MPa, 161 MPa and 122  MPa at room temperature, 600 °C, 800 °C and 1000 °C, respectively.