Grain growth stagnation in the dense nanocrystalline yttria prepared by combustion reaction and quick pressing with an ultra-high heating rate

Combustion reaction plus quick pressing was a developing technique that used the Joule heating effect of combustion reaction to sinter ceramics, and allows very high heating rate, short soaking duration and high pressure for densification of ceramics. By taking advantages of the particular conditions of this method, pure yttria ceramics with a relative density of 98.5% and an average grain size of 50 nm were obtained at 1620 K and 170 MPa. Moreover, the investigation on the grain growth of sintered yttria was carried out by analyzing the microstructure evolutions and responsible mechanisms. The combined effect of the ultra-high heating rate and the high pressure applied on compact at the peak temperature was effective in suppressing particle coarsening and enhancing densification. Besides, under the decreased sintering temperature and soaking duration, the retained nanostructure assisted to inhibit final-stage grain growth while without impeding the further densification of nanocrystalline ceramics.