化学気相析出法によるSiC/C系傾斜機能材料の合成と評価

概要

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SiC/C Functionally Gradient Materials(FGM) were prepared by chemical vapor deposition (CVD). SiCl4, CH4 and H2 were used as source gases. Non-FGM of SiC/C molar ratio with 0-1 were obtained by changing the ratio of SiCl4/CH4 in a temperature range of 1300-1500°C and in a pressure range of 10-100 Torr. Several non-FGM with various SiC/C ratio were subjected to the evaluation of mechanical properties and thermal properties. Modified SP test showed that fracture stress and Youngs moduli of non-FGM changed with SiC/C ratio. Relationship between mechanical properties and SiC/C ratio, however, did not follow the rule of mixture(R.O.M.).Coefficient of thermal expansion of non-FGM did not change widely within a range of C=0-80mol%.Non-FGM with carbon content of 90-100mol% showed anisotropy. Thermal conductvity of non-FGM also did not follow R.O.M.. The reasons for the non-R.O.M. tendency seemed to be (1) Porosity in SiC/C mixture (2) Preferred orientation of carbon (3) SiC skelton structure even in non-FGM with low SiC/C ratio. Finally FGM of SiC/C were prepared by changing the ratio of SiCl4/CH4 stepwisely or conteniously. FGM or step FGM could be deposited not only on graphite plate, but also on carbon fibers and also cylindrical graphite tube. Microscopic observation revealed that CVD technique could be useful for the preparation of FGM on the substrate with complex shape.