Fabrication and properties of 3D oxide fiber-reinforced Al2O3–SiO2–SiOC composites by a hybrid technique based on sol–gel and PIP process

Three-dimensional (3D) Nextel™440 fiber-reinforced Al2O3–SiO2–SiOC matrix (N440/ASS) composites were fabricated by a hybrid technique based on sol–gel and PIP process, employing diphasic Al2O3–SiO2 sols and polysiloxane. The sol–gel derived Al2O3–SiO2 ceramic was composed of 59.1 wt% Al2O3 and 39.8 wt% SiO2, and the element composition of the polymer-derived SiOC (PDC-SiOC) ceramic was SiO1.31C2.22 with excess carbon (~29.7 wt%). The porosity, density, microstructure and mechanical properties of the composites were investigated. Results showed that the density of the composites increased while the porosity decreased as densification cycles of polysiloxane increased. Microstructure analysis revealed that the matrix pore even inner fiber bundle was partially filled with PDC-SiOC. N440/Al2O3–SiO2 (N440/AS) composites showed single long cracking behavior with low flexural strength (31.5 MPa), owing to high porosity and low matrix modulus. On the contrary, N440/SiOC composites showed typical brittle fracture behavior like monolithic ceramics with flexural strength of 45.9 MPa because of high matrix modulus and strong interfacial bonding. N440/ASS2 composites, densified by PDC-SiOC for two cycles, showed typical toughened fracture behavior with improved mechanical properties (flexural strength, 81.4 MPa; interlaminar shear strength, 29.5 MPa), even after thermal aging at 1000 °C for 100 h.