Pressureless sintering of HfB2-based ceramics as control rod materials: Synergistic effects of the sintering additive and solid solution

Abstract The effects of sintering additives (Boron and SiC) and solid solution (TiB2) on the densification of HfB2-based ceramics, processed by pressureless sintering, were investigated for potential applications as advanced control rod materials. The addition of B was found to improve the densification properties of HfB2 through removal of the oxygen contamination yet incurred unfavourable grain growth. SiC was able to further enhance the densification through a grain pinning effort, improving the microstructure. In combination with oxygen impurity removal by the addition of B, the solid solution of Ti into HfB2 contributed to further improving the densification by reducing the particle size of HfB2 powder, further promoting diffusion during sintering. The grain size of SiC phase was also reduced through the refinement of HfB2 powder via solid solution. The deployment of B and SiC sintering additives, alongside TiB2 solid solution, during pressureless sintering was found to be beneficial in the preparation of high density HfB2-based ceramics, increasing microstructure density and enhancing mechanical properties.