Toughness optimisation of ZrO2-TiB2 composites

Yttria-stabilised tetragonal zirconia (Y-TZP) composites with 30 vol. % TiB2 are fabricated by hot pressing in vacuum for I hour at 1450 degreesC. Commercial co-precipitated zirconia starting powder as well as a range of experimental powder mixture grades of monoclinic and coprecipitated 3Y-TZP powders were used to study the influence of the zirconia matrix composition on the fracture toughness of the composites. The observed variation in mechanical properties of the composites is explained in terms of the microstructure, the residual stresses due to the presence of TiB2 and the stabiliser content. Whereas the overall yttria content is very crucial, the residual stress is found to be an additional important parameter influencing the t-ZrO2 transformability that needs to be taken into account when optimising the toughness of the composites. Beside transformation toughening, crack deflection was identified as an active toughening mechanism in the composites. A simple approach to tailor the toughness of ZrO2-TiB2 composites is proposed.