CONSOLIDATION AND MICROSTRUCTURE OF ALUMINA-SiC COMPOSITES BY THE SPARK PLASMA SYSTEM AT LOW TEMPERATURE

The densification of pure Al2O3 and Al2O3-SiC composites (with 5%,10%, 20% and 30 % SiC) manufactured by the SPS process was remarkably enhanced due to additional diffusion mechanisms induced by the spark plasma even at low temperature (830 degrees C - 1050 degrees C). The densification enhancement was attributed to the acceleration of the diffusion process due to additional mass-transport mechanisms induced by the spark plasma. The onset for densification of Al2O3- SiC composites was delayed with increasing amounts of SiC compared with the pure Al2O3 compact, respectively. The delay of the densification is thought to be due to the decrease in the grain boundary and lattice diffusivity, resulting from the second phase SiC dispersion. Therefore, in the composite case, higher temperatures for fully densification should be required to supplement the decrease in the diffusivity, compared with pure Al2O3. The thermal conductivity of SiC material is higher than that of Al2O3 particularly at elevated temperatures and consequently, the addition of SiC might be expected to promote heat transfer from the graphite die to the compacts. Finally, the enhancement of densification for the SPS process can also be attributed by considering the additional diffusion due to Joule heating, impact force and the electric field effect in which the diffusion of ions for sintering is accelerated by an applied electric field. It is reported that the generation of spark plasma at the insulating particle-to-particle contact points enhance densification. The monoclinic moganiteSiO(2) was identified in the composite with 10% SiC particles as well as rombohedral alpha-Al2O3 and distortioned hexagonal and rhombohedral SiC polytypes. Also, a hexagonal AIC(0.5)O(0.5) compound was revealed in the composites with 5-20% SiC and cubic Si was identified only in the composition with 30% SiC