Effect of carbon fiber preform structures on the mechanical properties of Cf@PyC/SiC composites

Cf@PyC/SiC composites, using needle-punched preforms, 3D orthogonal woven preforms and 3D 4-step braided preforms (braiding angles of 10 degrees, 20 degrees and 30 degrees) as the reinforcement, were obtained through che-mical vapor infiltration (CVI) method. The tensile strength before and after oxidation of the composites were investigated, and the microstructure, appearance of fracture and phase component of the composites were also analyzed. The results show that the mechanical properties and oxidation resistance of composites are greatly affected by the preform structures. The tensile strengths of 3D 4-step braided composites with the braiding angle of 10 degrees are the best among all composites before and after oxidation, which are 266.40 +/- 16.98 MPa and 238.66 +/- 14.98 MPa. Before oxidation, the fibers and matrix at the fracture of 3D 4-step braided composites are in staggered distribution. The mechanical enhancement mechanisms of composites such as crack deflection, interface debonding and fiber pull-out, were beneficial to good per-formance and excellent mechanical properties. After oxidation, the deflection and branching effects of the interface on the crack are not fully manifested, and enhancement and toughening mechanisms are not fully played due to the oxidation of the carbon fiber and the PyC interface.(c) 2022 Published by Elsevier B.V.