Carbon Dioxide Laser Cutting of a Carbon‐Fiber–Silicon Carbide‐Matrix Composite

Abstract

CO2 laser scribing and cutting were studied on a carbon‐fiber‐silicon carbide‐matrix (C/SiO) composite nominally containing 45 vol% of carbon fibers. The scribing and cutting were performed in continuous‐wave (CW) mode using laser powers between 750 and 1500 W, and specimen translation velocities between 0.5 and 4 cm/s. The laser spot size was 300 μm in diameter. The groove width and depth were measured as functions of power and velocity. The results were compared to theoretically predicted values obtained by solving the quasi‐steady‐state heat conduction equation in three dimensions for a moving body. Reasonably good agreement between theory and experiment was found. The microstructures of the laser‐cut surfaces indicated the formation of redeposit by condensation from the vapor phase. X‐ray diffraction and Raman spectroscopy analyses of the redeposit showed the presence of β‐SiC and graphitic carbon. The four‐point bending strength of the laser‐cut composite was found to be approximately 20% lower than the corresponding strength of the diamond‐cut composite. The strength was fully recovered after removing 180 ± 10 μm of the material from the lased surface by grinding. The oxidation resistance of the laser‐cut and diamond‐cut composites was studied with a thermogravimetric balance at 1103°, 1304°, and 1402°C in air. The oxidation behavior at all investigated temperatures for both materials was dominated by a rapid initial mass loss due to the oxidation of carbon and a possible active oxidation of SiC, followed by a slow mass gain due to the passive oxidation of SiC. At 1304°C the rate of passive oxidation of SiC in the laser‐cut material was somewhat higher than in the diamond‐cut material. At 1402°C, the diamond‐cut surface oxidized more rapidly than the taser‐cut surface. The differences in oxidation rates were attributed to the differences in microstructure.