Irradiation Effects of Fiber and Matrix Induced by He⁺ Ion for High-Performance C/C Composites

Abstract

To optimize the performance of the carbon fiber reinforced carbon matrix (C/C) composites by controlling the microstructure for more reliable and safety application in thorium molten salt reactor (hereafter, TMSR), we have investigated the irradiation effects of fiber, matrix, and their interfaces in C/C composite induced by He+ ions and further reveal their corresponding micromechanism. Compared with fibers, an obviously fragmented surface morphology in matrix appears and then gradually becomes widespread around the surface of C/C composite with increasing dose of irradiation. This found is attributed to the breakage of crystallites observed by synchrotron-based grazing incidence X-ray diffraction (GIXRD) and the increase of defect state density revealed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, respectively. Three different microstructure evolutions in fiber, matrix and fiber-matrix interface induced by irradiation damage have been further revealed in detail by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). It is found that the layered structure gradually loses its initial ordering and the nanostructural degradation in carbon matrix is much more serious than that of the fiber, resulting in breaks and bends in the lattice with increasing dose. Observed by nanoindentation experiment, the enhancement of the hardness and modulus of the matrix is more significant than that in fiber, which can be attributed to the more obviously pinning of basal plane dislocations in the matrix due to lattice defects induced by He+ irradiation. These discoveries are properly contribute to improve the performance of the C/C composites by regulatory microstructure composition, such as fiber and matrix.