Effect of different interfaces on the mechanical properties of 3D Nextel 720/mullite composites

PyC and PyC/SiC interface layers were coated on the surface of Nextel 720 fibers by chemical vapor infiltration. The 3D Nextel 720/mullite composites were fabricated by precursor infiltration and pyrolysis using TEOS- AIP as precursor. The mechanical properties and rupture model of the 3D Nextel 720/mullite composites with PyC and PyC/SiC coating were analyzed. Results indicate that the rupture model is brittle rupture for the 3D Nextel 720/mullite composites with PyC coating, and the flexural strength is 56 MPa only, due to the forming of strong bonding interfaces between fibers and matrix in the 3D Nextel 720/mullite composites during the pyrolysis process. But gap/SiC composite interfaces resulted from PyC/SiC interface layers lead to a weak bonding between fibers and matrix. As an obstruct layer, SiC prevents fibers from contacting to matrix, and the gap results in the pulling-out of fibers. The rupture model of the 3D Nextel 720/mullite composites with PyC/SiC coating is toughness failure and the flexural strength reaches to 267.2 MPa.