Reactive hot pressing of ZrB2-based composites with changes in ZrO2/SiC ratio and sintering conditions. Part I: Densification behavior

ZrB2-SiC-ZrO2 composites were hot pressed in order to investigate the effects of adding nano-sized ZrO2 particles as well as the hot pressing parameters on the densification behavior of ZrB2-SiC composites. An L9 orthogonal array of the Taguchi method was employed to study the significance of each parameter such as the sintering temperature, time, the applied external pressure, and ZrO2/SiC volume ratio on the densification process. The statistical analyses revealed that among the mentioned parameters, the hot pressing temperature had a great influence over the densification. By being hot pressed at 1850 °C for 90 min under 16 MPa, fully dense ZrB2-based composites were obtained. The relative density of the composites decreased at first and then enhanced as a function of ZrO2/SiC ratio. Microstructural investigation of the fracture surfaces of the composites, which was carried out using the SEM analysis, showed the formation of new phases on the surfaces of SiC grains. The EDS and XRD analyses identified the ZrC as the newly formed interfacial phase due to the reaction between nano-ZrO2 and SiC. The ZrC acted as an adhesive interphase between the ZrB2/SiC grains, which could assist the sintering process.