Microstructures and mechanical properties of Sr2Nb2O7-toughened 3Y-TZP ceramics

The effects of sintering time upon microstructures and the mechanical properties were investigated for Sr2Nb2O7-toughened 3Y-TZP ceramics. The incorporation of Sr2Nb2O7 secondary phase significantly enhanced the fracture toughness of 3Y-TZP ceramics, and the toughening effect was noticeably influenced by sintering conditions through microstructural changes: the fracture toughness increased with increasing soaking time for compositions of x⩽0.01, but a slight decrease of fracture toughness with soaking time was observed for x=0.015, where x is the mole fraction of Sr2Nb2O7. The high fracture toughness, K1C, of 13.7 MPa m1/2, was achieved in the ceramic with x=0.005 sintered at 1500 °C for 6 h. This is almost a doubling of fracture toughness, compared to the specimens without Sr2Nb2O7. It should be emphasized that the high fracture toughness, K1C of 10 MPa m1/2(1.4 times that of the matrix) could be obtained even for the situation without transformable tetragonal phase where the phase transition toughening was not active and the piezoelectric/ferroelectric secondary phase played an important role.