Sintering highly dense ultra-high temperature ceramics with suppressed grain growth

Grain coarsening normally occurs at the final stage of sintering, resulting in trapped pores within grains, which deteriorates the density and the performance of ceramics, especially for ultra-high temperature ceramics (UHTCs). Here, we propose to sinter this class of ceramics in a specific temperature range and coupled with a relatively high pressure. The retarded grain boundary migration and pressure-enhanced diffusion ensure the proceeding of densification even at final stage. A highly dense TaC ceramic (98.6 %) with the average grain size of 1.48 mu m was prepared under 250 MPa via high pressure spark plasma sintering using a C-f/C die at 1850 degrees C. It was suggested that the final-stage densification is mainly attributed to grain boundary plastic deformation involved mechanisms. Compared to the usual sintering route using a high temperature (> 2000 degrees C) and normal pressure (< 100 MPa), this work provides a useful strategy to acquire highly dense and fine-grained UHTCs.