Densification and thermal properties of zirconium diboride based ceramics

The research presented in this dissertation focuses on the processing and thermomechanical properties of ZrB2 based ceramics. The overall goal was to improve the understanding of thermal and mechanical properties based on processing conditions and additives to ZrB2. To achieve this, the relationships between the thermal and mechanical properties were analyzed for ZrB2 ceramics that were densified by different methods, varying amounts of carbon, B4C, or TiB2 additions.;Four main areas were investigated in this dissertation. The first showed that decreased processing times, regardless of densification method, improved mechanical strength to >500 MPa. This study also revealed that lower oxygen impurity contents led to less grain coarsening. The second study showed that higher heating rates narrowed the grain size distribution, which resulted in strengths above 600 MPa. However, the decreased processing times led to retention of ZrO2, which decreased the thermal conductivity. The third study revealed that carbon additions interacted with ZrO2 and WC impurities introduced during powder processing to form (Zr,W)C, which led to higher thermal conductivity than ZrB2 with no carbon added. The last area examined the effect of solid solution additions on the electron and phonon contributions to thermal conductivity. The formation of solid solutions decreased thermal conductivity to <60 W/m•K compared to 93 W/m•K for nominally pure ZrB2 at 25°C.;Taken as a whole, this research adds insight into the fundamental aspects of microstructure and composition that control the thermal and mechanical properties of ZrB2. These changes impact thermal and mechanical properties, which control the performance of ZrB2 based ceramics.