Effects of Metal Additives (M=Ti, Zr) and Oxigen Content on the Thermal Decomposition of Si-M-C-O Fibers

SiC matrix composites in which Si-M(=Ti, Zr)-C-O fiber is used as the reinforcing fiber are materials with superior heat capability and damage tolerance. It is known that the fiber's oxidation and thermal decomposition characteristics have a significant influence on the durability of Si-M-C-O/SiC. We measured the weight change, oxide layer thickness, and crystallite size of Si-M-C-O fiber, and the X-ray absorption fine structure (XAFS) of Si-Zr-Cr-O fiber, when exposed in an ambient atmosphere and in a vacuum. We determined the thermal decomposition of the fiber exposed in an ambient atmosphere, and we analyzed the influence of the added metal elements (M=Ti, Zr) and the oxygen content on thermal decomposition based on the difference in thermal decomposition behavior due to the type of fiber and the exposure environment.The results indicated that, when in a vacuum, the oxygen content of the fiber had a significant influence on the thermal decomposition of the Si-M-C-O fiber and the nucleation of ZrC in the Si-Zr-C-O fiber. On the other hand, when in the ambient atmosphere, in comparison with the behavior of ZrC in Si-Zr-C-O (1), TiC in Si-Ti-C-O (2) was formed at a lower temperature in a shorter time, indicating that resistance to thermal decomposition is greatly influenced by the type of metal added.