Microstructural mechanism and mechanical properties of C_f/SiC composite/ TC4 alloy joints composite-diffusion brazed with TiZrCuNi + TiC_p composite filler

摘要

in this paper, C-f/SiC composites and TC4 alloys were joined by the novel composite-diffusion brazing process using (Ti-Zr-Cu-Ni) + TiCp composite filler. The microstructural behavior and mechanism of the joints was deeply investigated by SEM, TEM and XRD. Mechanical properties versus different process parameters of the joints were thoroughly discussed. It was discovered that a reaction-breaking phenomenon occurred for TiC particles. During the bonding process, Zr atoms concentrated around TiC particles and reacted with them to form Ti(Zr)C compound layer on the surface of TiCp . As the reactions progressed, the Ti(Zr)C layer split into fine particles from TiC and then distributed uniformly in the joining layer together with the residual TiC particles. The smaller the TiC particle was, the less time it took to complete the breaking and dispersion process. These low coefficient thermal expansion (CTE) particles were beneficial for releasing the joint residual stress and significantly improved the mechanical properties of the joints. The shear strength of the joints at room temperature (RT) showed a peak value as the bonding temperature was raised or the holding time was prolonged when the TiCp content kept constant. With the increase of TiCp content, the bonding temperature corresponding to the peak shear strength of the joints became higher, the holding time corresponding to peak shear strength of the joints became longer. The shear strength of the joints at 800 degrees C had similar variation trend with the changing of bonding temperature, holding time and the content of TiCp . But, compared with the RT shear strength, the shear strength of joints at 800 degrees C was much smaller and the peak shear strength corresponded to longer holding time. The maximum shear strength of the joints at room temperature and 800 degrees C were 224 MPa and 157 MPa respectively.