Microstructure and mechanical properties of SiC bonded joints prepared by CVI

In this study, the C/SiC two-layer beams with SiC bonded joints were prepared via chemical vapor infiltration (CVI), and the microstructure characteristics as well as the shear properties of the SiC bonded joints were studied. It was found that the density of the SiC bonded joints is inhomogeneous and the bonding areas formed during the CVI process were not continuous. To understand the effect of the SiC bonded joints on the mechanical behavior of C/SiC two-layer beam, bending tests were conducted. Based on the results of the bending tests, the shear properties of the SiC bonded joints were evaluated by the composite beam theory, and the average values of the effective shear stiffness and the effective shear strength were 15.5 GPa and 7.8 MPa, respectively. Moreover, the relationship between the shear properties and the porosity of SiC bonded joints was studied, and the porosity was deduced to be 56.4% on average. Finally, the failure morphologies of the SiC bonded joints were observed. The results of failure analysis indicate that both SiC particles and carbon fibers can contribute to the shear strength of the SiC bonded joints.