Micro-mechanical properties and interfacial engineering of SiC fiber reinforced sol-gel fabricated mullite matrix composites

The toughening mechanisms of a SiC fiber reinforced sol-gel fabricated mullite matrix composites were studied by combining the microstructure, the micro-mechanical properties (especially the interface) and the macro fracture resistance by a bottom-to-up mechanical characterization method (transmission electron microscopy, nanoindentation, fiber push-in, digital image correction, etc.). The results show a chemical-reaction controlled fiber/matrix interface in the as-fabricated composite, leading to pretty strong interfacial shear strength (~537 MPa), measured by the fiber push-in tests. Interfacial engineering by chemical vapor deposited pyrocarbon interphase can effectively hinder the interfacial reactions and weaken the interfacial interactions. The low shear strength of the tailored fiber/matrix interface (~155 MPa) could trigger the toughening mechanisms like interface debonding, fiber pull-out, etc., when the composite was subjected to external bending stresses. Finally, the fracture toughness of the novel composite was found significantly enhanced from ~0.8 MPa√m to ~8.3 MPa√m, after the interfacial engineering with pyrocarbon interphase. Keywords: Mechanical properties, Interfaces, Crack/cracking, Chemical vapor deposition, Composites