Microstructure and mechanical properties of sinter-HIPed ZrO2–ZrB2 composites

In the area of the advanced materials, there exists a persistent need to develop tougher, stronger and harder ceramics. In the present work, we report the microstructure and properties of hard and tough ZrO2 composites reinforced with 30 vol.% ZrB2 particulates, processed using sinter-HIPing (Hot Isostatic Pressing) route. The influence of ZrO2 matrix composition (Y2O3 content) on the microstructure and mechanical properties of the sinter-HIPed composites is investigated. While the presintering was carried out in argon at 1400 °C, subsequent HIPing of presintered samples was carried out at 1400 °C for 1 h under 110 MPa argon pressure. The fully dense sinter-HIPed microstructure is characterized by the dispersion of ZrB2 particles (1–3 μm) in submicron ZrO2 matrix. An important outcome of the present work is that an excellent combination of hardness (upto 20 GPa) and toughness (upto 18 MPa m1/2) is measured, for the first time, in ZrO2-based composites. The microstructure-property correlation is discussed with particular importance to understand the underlying microstructural reasons for the enhanced mechanical property. The measurement of fracture surface m-ZrO2 content indicates that the transformation toughening phenomenon is an active mechanism for toughness enhancement. Additionally, crack deflection toughening by ZrB2 particulates also contribute to toughening of the composite.