飞秒激光加工参数对RB-SiC表面形貌的影响

Effect of Femtosecond Laser Processing Parameters on RB-SiC Surface Morphology

目的揭示飞秒激光加工参数对反应烧结碳化硅(Reaction-Bounded Silicon Carbide,RB-SiC)表面形貌的影响规律。方法通过改变激光能量密度和有效脉冲数,研究RB-SiC表面烧蚀槽的形貌变化规律,确定飞秒激光加工RB-SiC的去除机理。采用扫描电镜、共聚焦显微镜、X射线能谱仪和拉曼光谱仪分析RB-SiC烧蚀前后的表面形貌演变行为。结果激光能量密度在0.62~10.48 J/cm^(2)时,Si富集区域形成凹陷结构,SiC颗粒区域形成周期性结构(Laser-Induced Periodic Surface Structures,LIPSS),周期约为970 nm。随着激光能量密度的增加,凹陷结构扩大加深,表面球形纳米颗粒增多,烧蚀槽宽度呈对数增长。有效脉冲数在69~1379,Si富集区域的去除量高于SiC颗粒区域的去除量。随着有效脉冲数增加,烧蚀槽深度显著加深,凹陷结构扩展成深坑结构,飞溅至烧蚀槽外侧的纳米颗粒聚集成团簇物,由Si、SiC和非晶态SiO_(2)构成的沉积物在烧蚀槽边缘形成堆积层。结论降低激光能量密度能够减少RB-SiC表面凹陷和纳米颗粒,有助于提升烧蚀形貌的一致性。增加有效脉冲数会促进烧蚀槽底部深坑结构的产生,进而扩大Si与SiC去除量之间的差异。

The work aims to reveal the effect of femtosecond laser processing parameters on the surface morphology of reaction-bounded silicon carbide(RB-SiC).RB-SiC was cut into a sample of 30 mm×20 mm×3 mm,and then the surface was cleaned and polished with diamond abrasive paper.During the experiment,by femtosecond laser micromachining system and HR-Femo-IR-200-40 fiber femtosecond laser,grooves were processed on the surface of RB-SiC by changing the laser energy density and effective pulse number.The moving speed of the laser beam was 40 mm/s,the repetition frequency of the laser pulse was 200 kHz,and the focal length was 70 mm.The surface morphology of RB-SiC before and after ablation was observed by field emission scanning electron microscope,the change rule of RB-SiC surface ablation morphology was clarified,and the material removal mechanism of femtosecond laser processing RB-SiC was determined.The width and depth of the groove were measured by the laser confocal microscope,and the data obtained were fitted and analyzed by the least square method.The element distribution and material changes in RB-SiC micro-area before and after ablation were analyzed by X-ray energy spectrometer and DXR Raman spectrometer.The initial surface morphology of RB-SiC could be divided into two areas:the Si enriched area composed of 3C-SiC and Si,and the SiC particle area composed of 6H-SiC.When the laser energy density was in the range of 0.62-10.48 J/cm^(2),the molten Si and 3C-SiC in the Si enriched area would be removed and then a concave structure would be formed.The SiC particle area would be ablated to form a laser-induced periodic surface structures(LIPSS)with a period of about 970 nm,which was generated by the interference of laser beam and plasma wave.Due to the condensation and adhesion of silicon vapor,the silicon content on the processed SiC surface was relatively high.With the increase of laser energy density,the concave structure expanded and deepened,a large number of oxygen-containing spherical nanoparticles were produced on the ablated surface,the SiC was decomposed to form a new carbon substance,and the width of the ablated groove increased logarithmically.When the effective pulse number was in the range of 69-1379,the removal depth between the two areas was different,and the removal depth of the Si enriched area was always higher than that in the SiC particle area.With the increase of effective pulse number,the depth of the ablation groove increased significantly,the concave structure further expanded into a deep pit structure,the nano-particles splashed to the outside of the ablation groove to form clusters,and the deposits composed of Si,SiC and amorphous SiO_(2)formed an accumulation layer at the edge of the ablation groove.The results show that reducing the laser energy density can reduce the surface concave structure and nano-particles of RB-SiC,which is helpful to improve the consistency of ablation morphology.Increasing the number of effective pulses will promote the generation of deep pit structure at the bottom of the ablation groove and then the difference between Si and SiC removal will be expanded.