Microstructure evolution and mechanical properties of Ti₂AlNb-C/C joints brazed with Ag-Cu filler

Owing to their own unique advantage in performance, joining of Ti₂AlNb alloy to C/C composite is of importance. In this work, Ti₂AlNb alloy and C/C composite was bonded by vacuum brazing with Ag-Cu filler. The effects of brazing temperature and holding time on microstructures and mechanical properties of brazed joints were studied; the formation of brazing interface was discussed systematically. The typical microstructure consisted of Ti₂AlNb substrate /Ti₃(Cu,Al)₄+ (Nb,Ti)ss/AlCu₂Ti+ (Nb,Ti)ss/AlCu₂Ti+Cu(s,s)+Ag(s,s)/AlCu₂Ti/TiC/C/C composite substrate. The findings indicated that the inadequate brazing temperature or holding time prevented the formation of a continuous TiC layer. As the brazing parameters increased, the diffusion layer and reaction zone next to Ti₂AlNb alloy expanded, while the Ag-Cu eutectic structures diminished. Furthermore, AlCu₂Ti islands enlarged, and the compound layer beyond TiC phase thickened progressively. The mechanical properties of brazed joints were jointly determined by the quality of the TiC layer and the residual stress at the interface. Optimal brazing at 850 °C for 10 min resulted in a robust joint with a maximum shear strength of 38.7 MPa, attributed to a continuous TiC layer and sufficient plastic phases within the brazing seam.