Properties and Process of SiC Preparation by Spark Plasma Sintering

In this work, SiC ceramics were prepared by spark plasma sintering (SPS) using alumina and rare earth oxides (RE2O3, RE = Gd, Y, Sc) as liquid phase sintering additives. Displacement shrinkage curve with the temperature, as well as with temperature and time, has been drawn by recording the displacement, time, and temperature of the device’s indenter Then, the shrinkage displacement curves were employed to investigate the sintering process. The microstructure and the phase composition of the sintered samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that the sintering process involves physical shrinkage, gas expansion, displacement stagnation, and liquid phase formation. The maximum linear shrinkage occurred at the stage of liquid phase formation. A similar trend for shrinkage displacement curve formation was observed at the first three stages for all samples. At the same time, different shrinkage temperatures and shrinkage rates were noticed on the fourth stage. After sintering, equiaxed grains with a grain size of about 1–2 μm were observed for all samples. The extremely high heating rate and short holding time of the SPS process prevent grain growth. Secondary phase Y3Al5O12/Gd4Al2O9 formed with Al2O3 + Y2O3 and Al2O3 + Gd2O3 additives, respectively, was used as liquid phases. Sintered samples exhibited superior mechanical properties, high electrical resistance, and lower thermal conductivity due to the low conductive secondary phase and small grain size.