The radial microstructural in carbon fibers is important for their mechanical properties. Microstructures at different locations in the radial direction produced by heat treatments from 1350 to 2400 °C and their relationship to the mechanical properties were investigated by Raman spectroscopy, elemental analysis, X-ray diffraction, high-resolution transmission electron microscopy and mechanical testing. Results indicated that the differences of the shift and full widths at half maxima (FWHM) of the Raman G and D bands at different points in the radial direction from the skin to the core, showed minima while the tensile strength of the fibers was a maximum at 1700 °C heat treatment temperature. The maximum tensile strength of carbon fibers at 1700°C was ascribed to the smallest skin-core variation at this temperature. The FWHM of the G and D bands from the same points in the radial direction decreased with heat treatment temperature, indicating an increased uniformity of the vibration modes of both G and D bands The sizes and the orientation degree of the crystallites increased with heat treatment temperature, leading to an increase of tensile modulus. Non-carbon elements were preferentially released, and crystallites were preferentially grown and orientated in the skin region compared to those in the core due to the preferential heat absorption in the skin, leading to the lower values of FWHM of G and D bands in the skin than in the core. The Raman shift of the G band had a maximum at 1700 °C while that of D band decreased with heat treatment temperature at the same radial points of the fibers. The fact that the release rate of non-carbon elements increased with heat treatment temperature below 1700 °C could be responsible for the increased G band shift below 1700 °C. With a continuous decrease in the non-carbon element content, this effect was lessened and the improvement of the perfection of the graphite structure became dominant above 1700 °C.

碳纤维的径向微观结构对于其机械性能很重要。通过拉曼光谱，元素分析，X射线衍射，高分辨率透射电子显微镜和机械测试研究了在1350至2400°C的热处理条件下沿径向不同位置产生的微观结构及其与机械性能的关系。结果表明拉曼G和D的位移和半高全宽（FWHM）的差异在从皮肤到芯的径向不同点上的带显示出极小值，而在1700°C的热处理温度下纤维的拉伸强度最大。碳纤维在1700°C时的最大拉伸强度归因于该温度下最小的皮芯变化。径向相同点的G和D波段的FWHM随着热处理温度的降低而降低，表明G和D振动模式的均匀性均增加带随着热处理温度的增加，微晶的尺寸和取向度增加，导致拉伸模量增加。与皮肤中的核心相比，非碳元素优先释放，并且在皮肤区域中优先生长和定向微晶，这是由于皮肤中的优先吸热，导致皮肤中G和D带的FWHM值较低比核心。G带的拉曼位移在1700°C时最大，而D带的拉曼位移最大。在相同的纤维径向点处，带随着热处理温度而降低。非碳元素的释放速率随热处理温度低于1700°C而增加的事实可能是导致低于1700°C的G带位移增加的原因。随着非碳元素含量的不断降低，在1700°C以上，这种作用减弱，石墨结构的完善性成为主要问题。