Effect of C/C composite surface pretreatment on properties of brazed joint

The high temperature brazing of C/C composite and TiAl alloy was realized using BNi-2 filler metal under the condition of 1030 °C/20 min, less than 10−3 Pa. Surface pretreatment of C/C composite was carried out to adjust the interface structure of brazed joint, to explore the method of improving joint strength. The microstructure of the interface was observed by SEM, and the phase composition was detected by EDS and XRD. The shear strength of brazed joints was tested, and the fracture behavior and joining mechanism were also investigated. During brazing, Ti, Cr, and other carbide forming elements diffused to C/C composite side, forming Cr3C2, Cr7C3, TiC and other carbides, realizing metallurgical joining between the brazing filler metal and C/C composite. The microstructure of the interface of C/C-TiAl brazed joint was: TiAl alloy → TiAl + AlNi3 → AlNi2Ti → Ni(s, s) + Ti3Al + Ni3Si → Ni(s, s) + Ni3(Si, B) + CrB → Ni(s, s) + Ni3Si + TiCr2 → (Ti, Cr)C → C/C composite. The joint form and fracture path of the brazed joint on surface pretreated C/C composite side were changed. The average room temperature shear strength of surface pretreated C/C-TiAl brazed joint was 14.8 MPa, which was about 50% higher than that of brazed joint without C/C composite surface treatment.