The effect of heat treatment on the structural development and mechanical properties of carbon fibers

Abstract

Carbon fibers have been of great interest in many industrial applications due to their high specific mechanical properties. The tensile strength of the polyacrylonitrile (PAN)-based commercial carbon fiber is as high as 7 GPa, and the highest tensile modulus is about 600 GPa although the theoretical properties of carbon-carbon bonds are known to be 150 GPa and 1060 GPa, respectively. The property discrepancy is attributed to the defective structures including voids and structural heterogeneity. In addition, carbon fibers are often subjected to extreme environment such as high stress and high temperature, which may change their microstructure and properties. In this study, we have heat-treated commercial carbon fibers as high as 2400 °C without applying external stress, and traced the changes in microstructure using Raman spectroscopy, wide-angle X-ray diffraction, and X-ray photoelectron spectroscopy. The tensile testing and nano-indentation experiment were also conducted to examine the correlation between the microstructural variation and corresponding mechanical properties. The structure-property relationship of carbon fibers upon high temperature heat treatment will be presented.