Influence of the microstructure evolution of ZrO2 fiber on the fracture toughness of ZrB2–SiC nanocomposite ceramics

ZrB2–SiC nanocomposite ceramics toughened by ZrO2 fiber were fabricated by spark plasma sintering (SPS) at 1700 °C. The content of ZrO2 fiber incorporated into the ZrB2–SiC nanocomposites ranged from 5 mass% to 20 mass%. The content, microstructure, and phase transformation of ZrO2 fiber exhibited remarkable effects on the fracture toughness of the ZrO2(f)/ZrB2–SiC composites. Fracture toughness of the composites greatly improved to a maximum value of 6.56 MPa m1/2 ± 0.3 MPa m1/2 by the addition of 15 mass% of ZrO2 fiber. The microstructure of the ZrO2 fiber exhibited certain alterations after the SPS process, which enhanced crack deflection and crack bridging and affected fracture toughness. Some microcracks were induced by the phase transformation from t-ZrO2 to m-ZrO2, which was also an important reason behind the improvement in toughness.