Study of the effect of the impurity composition of silicon on the defectiveness of reaction-bonded silicon carbide samples

Abstract

Large-sized complex-shaped silicon carbide products can be obtained via liquid silicon infiltration, however, the presence of free silicon in their composition limits the scope of their application. The silicon content can be reduced by forming a fine-grained porous structure of the material and control of the growth rate of the carbide layer on the pore walls during liquid-phase silicification. We present the results of studying the effect of the impurity composition of silicon grade KR00 on the appearance of defects in the structure of fine-grained reaction-bonded silicon infiltrated silicon carbide (The results obtained can be used in the production of tribotechnical parts, valves, etc. on the basis of RGCC.). It is shown that iron contained in industrial silicon KR00 exerted the greatest effect. At a content of Fe below 0.94 %wt., SiSiC samples are almost defect-free with the density not less than 3.00 ± 0.05 g/cm3. At a Fe content of 1.49 %wt., defects in SiSiC samples are observed in the form of under-impregnated regions, which are probably attributed to the increased solubility of carbon in the silicon melt upon impregnation with technical silicon with an increased iron content and, as a consequence, more intensive growth of the silicon carbide layer on the pore walls with their subsequent overlapping. As the melt moves deeper into the carbonized porous sample, it becomes depleted in silicon with an increase in the content of impurities, primarily Fe and Al, and the formation of SiC, Fe3C, and FeSi. The theoretical calculation showed that the relative changes in volume for the reactions of SiC and Fe3C formation upon interaction of 1 mole of carbon with silicon and iron are 134 and 339%, respectively. Moreover, with a significant content of iron in the melt, a significant role in the overlap of capillaries can be played by the volumetric change associated with the formation of Fe3C. The results obtained can be used in the production of SiSiC-based tribotechnical parts, valves, etc.