Research On The Laser Water Jet Manufacturing Technology Of Silicon Carbide Fiber Reinforced Ceramic Matrix Composites

SiC Fiber reinforced Ceramic Matrix Composites(SiC_f/SiC)are widely applied in the aerospace industry due to the excellent material natures such as high strength and toughness,low thermal expansion coefficient and density.The fabrication of groove,cutting and micro hole of SiC_f/SiC has become a vital issue for the employment of heat shield of aircraft engine afterburner.Conventional machining,electrical discharge machining and laser machining are commonl y utilized for the manufacturing of these micro structures on SiC_f/SiC.Nonetheless,various deficiencies are exposed during their application,for instance,machining precision and quality.Meanwhile laser water jet(LWJ)machining has been paid extensive attention by researchers because of its unique superiorities.Compared to other machining technologies,high machining quality,low heat affected zone and recast layer could be obtained with LWJ.Moreover,the conflicts among precision,efficiency and low damage in SiC_f/SiC machining could be solved by LWJ prospectively.In this work,the method of nanosecond laser combined with micro water jet is proposed for precision manufacturing of SiC_f/SiC,including the research of groove,cutting and micro hole.Furthermore,LWJ machining confined with coaxial gas is put forward,which provides a significant technological means for high quality and efficiency fabrication of composites.Firstly,the physical model of laser induced water ionization is established referring to Fokker-Planck equation.Evolution mechanism of electron concentration is explored during the interaction between laser and water,as well the laser parameters.In this paper,beam envelope method is proposed to investigate the energy distribution,attenuation and waveform evolution inside the coupling jet with numerical calculation.Furthermore,verification tests are carried out to evaluate and analyze the energy distribution and laser power.Besides,single-point multi pulses ablation experiment on suitable target material by LWJ is raised to validate the accuracy of theoretical model of coupling jet.Secondly,the machining system of nanosecond laser combined with micro water jet and coaxial constraint gas is established according to the laser parameters selection.On the basis of machining system,volume of fluid method is selected to describe the gas-liquid two-phase flow model of coaxial helical/annular gas atmosphere.The influences of gas component,pressure and intake type on the jet stability and coherence are analyzed with numerical simulations and experiments.Argon,nitrogen and compressed air are employed for coaxial helical gas atmosphere,as well the compressed air is chosen for coaxial annular atmosphere.To compare the processing capacity improvement of LWJ under different gas constrained atmospheres,the groove depth of single-row scribing experiments are carried out identically.Thirdly,photo-thermal model of LWJ is set up based on the first law of thermodynamics combined with imping and cooling effect of water jet.Geometric topological modeling of SiC_f/SiC is realized with Layer wise Theory(LWT)and Unit cell method(UCM),meanwhile a representative unit is selected to describe the interaction between SiC_f/SiC and LWJ.Then the evolution and distribution of temperature field on material surface is studied with different laser pulse energy.Moreover,the evolution mechanism of materials removal is investigated through numerical simulation and scribing experiments.Finally,the basic tests of processing technology are researched with LWJ.The laser with different pulse widths and wavelengths are adopted for single-row scribing on SiC_f/SiC surface.With the morphology of grooves and EDS analysis,processing quality of different methods are evaluated directly.A series of single-row and multi-row scribing experiments are carried out to explore the influence law for groove morphology between chamber pressure,pulse energy and scribing speed.In addition,single-point and turn-by-turn concentric circle drilling methods are adopted to investigate influencing mechanism of LWJ parameters on micro hole morphology.The influence of different operating conditions on the morphology of micro hole is also analyzed with experiments.With the analysis of experimental results,the application fields of LWJ confined with coaxial gas are further summarized.Moreover,tensile tests are developed to discuss the influence for tensile strength and fracture property of micro hole sample fabricated by different methods.