Densification of nano-SiC by ultra-high pressure effects of time, temperature and pressure

Abstract

High density SiC ceramics with 4 wt.% (in mass) and without Al 2O 3 as sintering additive were fabricated by nano-SiC as raw materials under different technical condition (1000–1300 °C, 4.0–4.5 GPa, 15–35 min) using China-type twain face anvils apparatus. The effect of sintering parameters on the mechanical property of SiC ceramics was studied. The sintered SiC was characterized by XRD, SEM, EDS and micro-hardness instruments. The results indicated that pure SiC could be sintered to high density (SiC sintered at the condition of 4.5 GPa/1250 °C/35 min could reach 96% of its theory density) by ultra-high pressure technique, and Al 2O 3 is a kind of effective sintering additive, SiC doping with only 4% Al 2O 3 could be sintered to full density by ultra-high pressure technique. The grain size was kept in nano-scale, its crystal lattice shrinkage was about 0.45%, while β-SiC has not changed. The micro-hardness and density were increased with increasing sintering temperature, pressure and holding time. The ultra-high pressure method could effectively lower the sintering temperature, shorten the sintering time and reducing the usage of sintering additive. Under 4.5 GPa the lowest sintering temperature was 1300 °C, which was above 600 °C lower than that for conventional liquid-phase sintering and its density is much higher.