The effect of laser irradiation on the microstructure and properties of PAN-based carbon fiber during graphitization

Carbon fibers (CF) with highly ordered graphitic structure are in demand for various applications. This study introduces fiber laser graphitization that offers a novel approach to enhance the properties of carbon fibers by utilizing precise laser irradiation to induce graphitization of PAN-based carbon fibers. The structural and mechanical properties changes were assessed through different detection and characterization techniques. Upon graphitization at different laser powers, Raman spectra revealed graphitic order features and a significantly increased degree of graphitization. The structural analysis showed an increase in both the out-of-plane (Lc) and in-plane (La) crystallinity, along with the preferred orientation of crystallites in the axial fiber directions. The surface morphology revealed a rough structure attributed to the fast energy supply from the laser power. The HRTEM lattice-fringe showed the growth of graphene layers and the rearrangement of graphite lamellar. The increase in tensile modulus was attributed to changes in crystalline size that outlined the rearrangement and the tensile strength decreased due to both residual stresses and structural defects that were introduced during processing. This research highlights fiber laser as a method to develop carbon fibers with a microstructure that is ultimately beneficial to achieve enhanced mechanical properties while also achieving a high degree of graphitization.