Effect of Fabrication Process on Internal Friction of SiC/SiC Composites

Silicon carbide (SiC) based fiber reinforced SiC composites have been fabricated by various methods which are, for example, polymer impregnation and pyrolysis (PIP), hot press (HP) and chemical vapor infiltration (CVI) processes. It is also well known that there are many differences in the density, the elastic modulus and the strength of composites made by those methods. In this paper, the effect of fabrication process on the internal friction of SiC/SiC composites was studied. From the temperature dependences of internal friction and elastic modulus of composites made by PIP, HP and CVI processes, a suitable method to make the high-damping SiC-based composite with a good elastic property is considered to be CVI process. In the case of the composite produced by CVI process at 1323 K, a stable peak of internal friction due to the grain boundary relaxation was obtained at about 1200 K. The temperature of this peak moved to the lower side after heat treatment at 1773 K. Also, it was found that the peak was not affected by the property of the SiC based fiber but by the microstructure of the matrix.