Mechanical properties of unidirectional laminated hybrid SiC-NextelTM 720 fiber-reinforced oxide matrix composites fabricated by a novel precursor infiltration and pyrolysis method

Unidirectional laminated hybrid SiC-NextelTM 720 fiber-reinforced yttria-stabilized zirconia-mullite composites were fabricated by a novel precursor infiltration and pyrolysis method. The effect of annealing atmosphere (Ar and air) at 1200 degrees C on the mechanical properties and failure mechanism of the composites was investigated. The Ar-annealed composite had a superior flexural strength of 337.1 +/- 5.7 MPa and a good fracture toughness of 13.3 +/- 0.1 MPa m1/2, and exhibited non-brittle failure behavior. However, the Air-annealed composite had a poor flexural strength of 102.8 +/- 0.8 MPa and a low fracture toughness of 5.3 +/- 0.3 MPa m1/2, and it exhibited brittle failure behavior. Further analysis indicated that the presence of a considerable amount of residual carbon in the Ar-annealed composite effectively weakened the fiber/matrix interface by reducing the residual radial compressive stress and the interfacial coefficient of friction. The weak interface could trigger toughening mechanisms in the composite, such as fiber pullout and debonding, and crack deflection. The mechanical degradation of the Air-annealed composite was also associated with the slight damage of NextelTM 720 and the oxidation of SiC fibers after exposure in a high-temperature air environment. The findings of this study provide guidance for designing new composites exhibiting high performance.