Processing and mechanical properties of ZrO2–TiB2 composites

In this paper, a strategy is described to develop high toughness yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) composites reinforced with hard TiB2 particles. The experimental results revealed that fully dense Y-TZP composites with 30 vol.% TiB2 can be obtained with a moderate hardness of 13 GPa, a high strength up to 1280 MPa and an excellent indentation toughness up to 10 MPa m1/2 by hot pressing in vacuum at 1450 °C. The toughness of the composites can be tailored between 4 and 10 MPa m1/2 by varying the yttria stabiliser content of the ZrO2 matrix between 3 and 2 mol%. An optimum composite toughness was achieved for a ZrO2 matrix with an overall yttria content of 2.5 mol%, obtained by mixing pure monoclinic and 3 mol% Y2O3 co-precipitated ZrO2 starting powders. An important observation is that the thermal residual tensile stress in the ZrO2 matrix due to the TiB2 addition, needs to be taken into account when optimising the transformability of the ZrO2 matrix in order to develop high toughness Y-TZP composites.