Densification and Thermal Properties of Zirconium Diboride Based Ceramics
MISSOURI UNIV OF SCIENCE AND TECHNOLOGY ROLLA
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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,WC, 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 Wm dot K compared to 93 Wm dot K for nominally pure ZrB2 at 25 deg 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.
- Ceramics, Refractories and Glass
- Properties of Metals and Alloys