Spark plasma sintering of Al$_2$O$_3$–SiC ceramics. Study of the microstructure and properties

The features of spark plasma sintering of submicron Al$_2$O$_3$ powders with different contents (0, 0.5, 1.5, 5 vol.%) of $\beta$-SiC nanoparticles have been studied. The microstructure and hardness of Al$_2$O$_3$ + 5 vol.% SiC ceramics obtained by sintering Al$_2$O$_3$ powders with $\beta$-SiC particles of various types (nanoparticles, submicron particles, fibers) have been studied. Sintering was carried out at heating rates $(V_h)$ from 10 to 700$^\circ$C/min. The sintering process of Al$_2$O$_3$ + SiC ceramics with low heating rates ($V_h$ = 10–50$^\circ$C/min) has a complex three-stage character, with a flat area in the temperature range of 1200–1300$^\circ$C. At high heating rates ($V_h>$ 250$^\circ$C/min), the usual three-stage character of sintering is observed. The analysis of temperature dependences of compaction was carried out using the Young–Cutler model; It was found that the kinetics of powder sintering is limited by the intensity of grain boundary diffusion. It is shown that the dependence of the hardness of Al$_2$O$_3$ + SiC ceramics on $V_h$ has a nonmonotonic character, with a maximum. In the case of pure alumina, an increase in $V_h$ leads to a monotonic decrease in hardness.