SIPM Makes Progress in Femtosecond Laser Processing Of Silicon Carbide Ceramic Matrix Composites

Recently, a research team from the State Key Laboratory of Intense-Field Laser Physics, Shanghai Institute of Optical Precision Machinery (SIPM), Chinese Academy of Sciences (CAS), in collaboration with a team of academician Shao-Ming Dong from the Shanghai Institute of Silicates, CAS, etc., has proposed and demonstrated a method to monitor femtosecond laser machining of silicon carbide ceramic matrix composites (SiC CMCs) based on the femtosecond laser filamentation of SiC CMCs and the monitoring of femtosecond laser machining process through filament induced plasma A method based on femtosecond laser filamentation processing of SiC CMC and monitoring of the process by filament-induced plasma fluorescence is proposed and demonstrated. The results of the study were published as "Femtosecond laser filament ablated grooves of SiC ceramic matrix composite and its grooving monitoring by plasma fluorescence" in the journal CCTV. The results were published in Ceramics International under the title "Femtosecond laser filament ablated grooves of SiC ceramic matrix composite and its grooving monitoring by plasma fluorescence.
Silicon carbide ceramic matrix composites, as a new generation of thermal structural materials, have significant advantages such as low density, high temperature resistance, corrosion resistance, high strength, etc., and therefore have great potential for application in aerospace, nuclear power, national defense, hypersonic transportation, etc. The high hardness and anisotropic nature of the SiC CMC material devices have put forward higher requirements and challenges for machining processes such as precision machining of curved surfaces and deep holes, etc. The results are summarized as follows. Machining. Traditional mechanical, waterjet, EDM, ultrasonic and other processing technologies are prone to burrs, delamination, cracks and other defects, and it is difficult to realize precision processing. Ultrafast laser processing, as a new system of "cold processing", is expected to meet the needs of high-precision and even over-precision SiC CMC processing.
In this work, the researchers through the femtosecond laser air filamentation, resulting in high-intensity, long interaction range of the filament, using the filament in the SiC CMC surface to complete high-precision groove processing, and systematic study of the filament position, laser pulse energy, scanning speed and scanning number of the width of the filament processed groove width, depth, heat-affected zone, the inner wall inclination angle and other parameters. The long interaction range characteristic of the light filament provides a new way for ultrafast laser precision machining of curved surfaces and deep holes. The study proposes and demonstrates a monitoring method for the process of SiC CMC processing by optical filament by collecting and analyzing the plasma fluorescence generated by optical filament processing of SiC CMC in real time, such as the 390.55 nm fluorescence of silicon atoms (Figs. 1 and 2). It is found that the variation of the intensity of the 390.55 nm fluorescence spectral line of silicon atoms directly responds to the SiC CMC surface material removal under different processing parameter conditions, which is helpful for understanding, monitoring and optimizing the process of photofilament processing of SiC CMC.
This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Key Project of International Cooperation of the Chinese Academy of Sciences, the Science and Technology Project of Shanghai Municipality, and the Project of Shanghai Scientific and Technological Achievement Transformation and Industrialization.

Fig. 1 (a) Schematic diagram of V-groove processed by optical filament, (b) and (c) photographs of top view and cross-sectional morphology of V-groove processed by optical filament, respectively, (d) photographs of lateral fluorescence of optical filament, and (e) and (f) original spectra and spectra with removal of continuum spectral background of plasma fluorescence induced by interaction of optical filament with SiC CMC, respectively.

Fig. 2 (a) Morphology of SiC CMC grooves processed by light filament at different laser energies, (b) contour curves of the depth profile of the groove cross-section at 2.4 mJ, (c) variation of the groove width, depth, heat-affected zone, and inclination angle of the inner wall with the laser energy, and (d) variation of the plasma fluorescence intensity with the laser energy.