Silicon nitride-based composites reinforced with zirconia nanofibres

Silicon nitride (Si3N4) ceramics exhibit remarkable mechanical, chemical and thermal properties; however, fracture toughness is a decisive characteristic for these advanced ceramics. In this paper, an alternative route to improve the fracture toughness of Si3N4 ceramics is presented. In order to enhance the fracture behaviour, we used ZrO2 nanofibres to combine two types of toughening effects such as fibre toughening and phase transformation toughening. We characterized the effect of nanofibers on the mechanical properties using instrumented hardness, Young's modulus, fracture toughness and bending tests. In order to compare the effects of nanofibers, we also studied silicon-nitride ceramics containing ZrO2 particles. The results of fracture toughness and flexural strength measurements show a significant improvement: 15 wt% ZrO2 fibre exhibits 10.05 +/- 0.7 MPa m(1/2) fracture toughness and 543 +/- 19 MPa flexural strength, which means 105% and 115% improvements compared to the reinforcement-free samples. We assume that ZrO2 nanofibres can increase the mechanical properties of the composites in a complex way, including phase transformation toughening and fibre-toughening mechanisms.