Sol-gel temperature dependent ductile-to-brittle transition of aluminosilicate fiber reinforced silica matrix composite

A thorough understanding in the micro mechanical properties of the fiber, the fiber/matrix and the matrix of the composite material, especially in response to different processing temperatures, is critical to explore the strengthening and toughening mechanisms of the novel oxide fiber reinforced oxide ceramic matrix composites. This work contributes this by studying the sol-gel temperature dependent micro mechanical properties of an aluminosilicate fiber reinforced silica matrix composite using novel nano-mechanical methods like nanoindentation and push-in techniques. In the sol-gel temperature range of 600-1200 °C, the aluminosilicate fiber was comparably stable in mechanical properties, though a microstructure transition from amorphous SiO2+ γ-Al2O3 to crystallized mullite+γ-Al2O3 was found at 1000 °C. The silica matrix was amorphous in microstructure, but were more crystallized as the sol-gel temperature increased, which subsequently led to an enhanced mechanical property at higher temperature. The interfacial shear strength was small in the temperature range of 600-1000 °C, and was increased slightly from ∼50 MPa at 600 °C to ∼84 MPa at 1000 °C. The interfacial shear strength at 1200 °C was high (∼256 MPa), due to the interfacial reaction occurring at this temperature. Correlating these micro mechanical properties to the macro fracture resistance that was quantified by the three-point bending test, an interface mediated toughening mechanism was finally concluded to explain the sol-gel dependent fracture resistance of the composite and the ductile-to-brittle transition observed in the temperature range.