Commercial ultra-high-strength PAN-based carbon fibers (T1000G) were heat-treated at the temperature range of 2300– 2600 °C under a constant stretching of 600 cN. After continuous high-temperature graphitization treatment, microstructures, mechanical properties and thermal stability of the carbon fibers were investigated. The results show that the T1000G carbon fibers present the similar round shape with a smooth surface before and after graphitization, indicating the carbon fibers are fabricated by dry–wet spinning. In comparison, the commercial high-strength and high-modulus PAN-based carbon fibers (M40JB and M55JB) present elliptical shapes with ridges and grooves on the surface, indicating the carbon fibers are fabricated by wet spinning. After graphitization treatment from 2300 to 2600 °C under a constant stretching of 600 cN, the Young’s modulus of the T1000G carbon fibers increases from about 436 to 484 GPa, and their tensile strength decreases from about 5.26 to 4.45 GPa. The increase in Young’s modulus of the graphitized T1000G carbon fibers is attributed to the increase in the crystallite sizes and the preferred orientation of graphite crystallites along the fiber longitudinal direction under a constant stretching condition. In comparison with the M40JB and the M55JB carbon fibers, the graphitized T1000G carbon fibers are easier to be oxidized, which can be contributed to the formation of more micropores and defects during the graphitization process, thus leading to the decrease in the tensile strength.

The microstructures and mechanical properties of ultra-high-strength PAN-based carbon fibers during graphitization under a constant stretching
    Abstract
    1 Introduction
    2 Experimental procedures
        2.1 Raw materials and high-temperature graphitization treatment
        2.2 Characterization of carbon fibers
    3 Results and discussion
        3.1 Crystal structure of carbon fibers
        3.2 Morphologies and microstructures of carbon fibers
        3.3 Oxidation behaviors and mechanical properties of carbon fibers
    4 Conclusions
    References

• Chong Ye(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Huang Wu(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Dong Huang(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Baoliu Li(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Ke Shen(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Jianxiao Yang(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Jinshui Liu(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University)
• Xuanke Li(College of Materials Science and Engineering, Hunan University/Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University/The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology)