SiCf/SiC复合材料纳秒激光烧蚀机理研究OA

SiCf/SiC composites,as a new type of material with excellent properties such as high specific strength,high temperature resistance,and corrosion resistance,have become one of the preferred materials for turbine blades of next-generation aerospace engines,and have been widely used in the automotive industry,nuclear reactors,and other fields.However,their high hardness,brittleness,weak electrical conductivity and other characteristics make them processing extremely difficult.Nanosecond laser ablation is a non-contact processing with high efficiency and a wide processing range,which has a broad application prospect in the processing of ceramic matrix composites. The quality of SiCf/SiC composites processed by a nanosecond laser is greatly affected by the process parameters.In this paper,SiCf/SiC composites were processed by a nanosecond laser with a wavelength of 355 nm,a pulse width of 15 ns,a spot radius of 15 μm,and a pulse repetition frequency of 80 kHz,and the effects of the laser energy density and the scanning speed on the size of the ablation groove and the composition of the physical phase were investigated.The morphological characteristics after ablation were analyzed by observing the microscopic ablation morphology with a field emission scanning electron microscope(HITACHI,SU5000),measuring the width and depth of the ablation grooves with a laser confocal microscope(Olympus,OLS4000).The changes of the material before and after ablation were analyzed by micro-Raman spectroscopy(Thermo Fisher,DXR Microscope)to reveal the ablation mechanism of nanosecond laser ablation of SiCf/SiC composites. The results show that the laser energy density mainly affects the ablation width,and the scanning speed mainly affects the ablation depth within the range of the selected process parameters.The laser energy density is increased from 1.78 to 8.89 J/cm2,and the ablation width is increased by 10.06 μm.The scanning speed is decreased from 800 to 50 mm/s,and the ablation depth is increased by 76.12 μm.The main ablation product of nanosecond laser ablation of SiCf/SiC composites is SiO2.Inside the ablation bath,due to the low partial pressure of oxygen and the high temperature,the passive oxidation of SiC is transformed into active oxidation,which generates substances such as SiO and CO.In addition,SiC decomposes and evaporates during the ablation process,which affects the content and crystallinity of SiC in the material.When the laser energy input per unit time absorbed by the material is small,the gas recoil pressure generated by SiC evaporation decomposition throws the molten droplets away,forming a semicircular sputtering shape near the spot.When the material absorbs a larger laser energy input per unit time,most of the molten droplets cannot leave the ablation bath,forming a thicker recast layer and blocky buildup in the ablation bath.