Silicon Carbide (SiC) ceramics belong to an important class of structural materials used for high temperature applications. The specific attributes that account for their utility as engineering ceramics are high value of thermal conductivity together with lower thermal expansion coefficient, thereby having higher thermal shock resistance. High mechanical strength also plays a vital role for considering SiC as structural components in various devices. However, it is difficult to densify SiC even at elevated temperature because of the covalent nature of its bond. In the present work, fine powder of ?-SiC mixed with sintering additives (Al, B, C) was hot pressed at 32 MPa in graphite die at various temperatures in the range of 1700-1900°C under vacuum. Hot pressing at 1900°C yielded a fully dense material. Optical micrographs showed presence of elongated grain of a-SiC. Fracture surface of SiC observed under scanning electron microscope (SEM) revealed the occurrence of liquid phase sintering. The grain boundaries appeared to be free of secondary phase as revealed from the bright field conventional transmission electron microscopy (TEM) images. High-resolution electron microscopy analysis, however, provided evidence for distribution of amorphous phase at the grain triple junction. Hardness and toughness of the hot pressed SiC were found to be in the range of 20-22 Hv_(0.1) and 2.5-3.0MPa.m respectively. Flexural strength of the highly dense samples was found to be in the range of 225-240MPa.
展开▼
