Microstructural Studies Of Ion Irradiated C/C Composites

C/C composites are an attractive and potential candidate of structural materialsfor nuclear reactors for their excellent high temperature stability, resistance tocorrosion and radiation. Fission products of liquid fuel may induce irradiation damageon structural materials in molten salt reactor. Therefore, it is necessary to study theirradiation effects on C/C composites induced by fission products. However, to ourknowledge, there are few irradiation experiments on the surface structure of C/Ccomposites caused by fission products. In the thesis, the irradiation effects of fissionproducts on the C/C composites were studied by using ions beam at different energies.The morphology and microstructure of the samples had been characterized by Ramanspectroscopy and scanning electron microscope.In the first part of the thesis, the studies on the matrix surfaces revealed thatdefects are created in C/C composites due to ion irradiation. According to the analysisof Raman spectroscopy, with increasing irradiation dose, the surface defects in theirradiated samples are significantly increased. By using the scanning electronmicroscope, some cracks and holes were found in the matrix surfaces, the largest onesare even up to the size of one micrometer. However, the matrix surface defects in thecarbon cloth layer and the mat layer are different. In addition, experimental resultsshowed that ion irradiation with lower energy can produce more damage in the matrixsurface. The mechanism is identified as follows: radiation damage depth caused bylow energy ions is more shallow than that by the high energy ones. Furthermore,sputtering of low energy ions is greater than the high energy ions.In the other part of the thesis, microstructural analysis were carried out on themorphology of the carbon fibers and the pyrolytic carbons before and after irradiation.It showed that the pyrolytic carbons around the carbon fiber are easily split andtwinned by ion beam irradiation. Moreover the interface between the carbon fibersand the pyrolytic carbons was found to be blurred after irradiation. Its mechanism is shown that the interstitial atoms generated by the irradiation can create a planebetween the existing planes. The new plane may destroy the lamellar structure ofpyrolytic carbons.