Benefits of Zr additive element in the Ti–24Ni eutectic filler in vacuum brazing of SiC ceramics

The SiC ceramics have been successfully brazed using Ti–24Ni (at. %) eutectic filler at 1030 °C with 15 min holding time. A Ti ₅ Si ₃ and TiC mixed reaction layer was formed adjacent to SiC substrate, while Ti ₂ Ni intermetallic compound was the major component in brazing seam area. It's found that the Ti ₂ Ni phase has extremely high coefficient of thermal expansion (CTE), and the residual stress caused by the CTE mismatch between Ti ₂ Ni and SiC is unfavorable for shear strength of the joints. Through adding 15 at. % Zr into the Ti–24Ni filler, α-Ti[Zr] solid solution with lower CTE as well as good ductility was generated in the joints, which was beneficial for relaxing the residual stress. Consequently, shear strength of the joints was improved from 69 MPa to 112 MPa at room temperature and from 36 MPa to 62 MPa at 600 °C, respectively.