Silicon carbide was hot pressing sintered at 1300 ̊C/30 MPa by using magnesium additive. Microstructure and sintering mechanism are studied. Result shows that the hot pressing sintered sample composed of both α-SiC and β-SiC, indicating that no polytype transition has happened. Magnesium with stacking faults is located on the silicon carbide matrix as second phase particles. Dislocations and stacking defaults are initiated from grain boundaries and move toward the interior. Micropores locate on grain boundaries, substructure and triple grain junction, revealing a boundary diffusion mechanism. Long-range dislocations in grains and substructures in the lattice confirm a power-law creep mechanism.www.hslabrasive.com
Silicon carbide offers excellent ceramic properties such as creep resistance, chemical stability, higher modulus, hardness and strength even at high temperature owing to its extra-strong covalent bond [1], [2]. So it is widely used in various industrial applications, including metallurgy, aerospace, environmental area, nuclear power plant and semiconductor industry [3]. However, due to the strong covalent binding energy between Si and C, silicon carbide is hard to be sintered, resulting in a high sintering temperature more than 1600 ̊C with conventional additives, such as B4C and Al [2], [3], [4], [5]. The high temperature not only increases energy consumption, but also brings potential safety hazards. Therefore, it is essential to develop high-quality sintered silicon carbide by more effective additives.
There is no doubt that liquid phase additives are more efficient than solid phase additives in lower temperature which act as a binder [6], [7]. Aluminum is a most widely used liquid phase additive in silicon carbide sintering. However, compositions such as boron, carbon or boron carbide must be added, resulting in a large content of impurity [8]. According to the results reported by Huang et al. [9] and Easton et al. [10], reaction products between silicon carbide and magnesium/aluminum have a crystal structure closer to magnesium than to that of aluminum. Due to this fact, magnesium may be a candidate liquid phase additive.silicon carbide for sandblasting
So far, no unanimous conclusion has been drawn on the mechanisms of liquid phase sintering of silicon carbide. And sintering mechanisms are commonly been investigated just by densification and grain growth data [11], [12], [13], which is rough and conditional-affected. To the best of our knowledge, investigations on microstructure of liquid phase sintered silicon carbide have not been systematically presented. In this paper, we propose a novel magnesium additive combine with a convenient hot pressing sintering process for preparing silicon carbide ceramic. The phase content, particle sizes and distribution, defects and substructures have been systematically investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The sintering mechanisms have been discussed according to microstructure features. |
