On Morphological and Microstructural Changes in Uranium Dioxide Powder during Binder-Free Hot Pressing

Plasticity of oxide fuel based on uranium dioxide is one of the less-covered topics in nuclear materials science. A useful tool to study the deformation mechanisms in this material at elevated temperatures is hot pressing. In this work, UO$_{2.06}$ powder prepared via~ADU route was uniaxially compacted at temperatures within the~$250$--$600$~{\textdegree}C range under a compressive axial stress from~$95$ to~$220$~MPa applied for a time interval between~$10$ and~$60$~min. Examinations performed with scanning electron microscopy~(SEM) and density measurements revealed a temperature effect on densification when increasing the compaction temperature from~$400$ to~$600$~\textdegree{C} with other conditions being equal. By varying the loading duration for hot pressing at~$600$~{\textdegree}C under constant compressive stress~$95$~MPa, different stages of compactions were analyzed. In addition,~XRD measurements revealed a texture developing in the material during compaction and a possible increase in dislocation density. It is argumented that dislocation-mediated plasticity contributes to densification at elevated temperatures.