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

ZrB 2 –SiC nanocomposite ceramics toughened by ZrO 2 fiber were fabricated by spark plasma sintering (SPS) at 1700 °C. The content of ZrO 2 fiber incorporated into the ZrB 2 –SiC nanocomposites ranged from 5 mass% to 20 mass%. The content, microstructure, and phase transformation of ZrO 2 fiber exhibited remarkable effects on the fracture toughness of the ZrO 2(f) /ZrB 2 –SiC composites. Fracture toughness of the composites greatly improved to a maximum value of 6.56 MPa m 1/2 ± 0.3 MPa m 1/2 by the addition of 15 mass% of ZrO 2 fiber. The microstructure of the ZrO 2 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-ZrO 2 to m-ZrO 2 , which was also an important reason behind the improvement in toughness.