为了研究影响飞秒激光烧蚀0Cr18Ni9不锈钢精度的因素, 采用飞秒激光对0Cr18Ni9不锈钢进行了切割和打孔实验。利用光学显微镜、光学金相显微镜等设备, 对不锈钢烧蚀区形貌和切缝显微组织进行检测, 基于烧蚀过程中CCD实时采集到的不锈钢表面的激光光斑图样, 采用COMSOL Multiphysic数值模拟软件, 模拟了烧蚀过程中激光束的发散传播行为, 并计算了光束发散角。结果表明: 当激光重复频率为5 kHz时, 厚度为160 μm的0Cr18Ni9不锈钢切缝和孔边缘被明显烧黑, 切缝处晶粒明显长大, 存在热影响区; 烧蚀过程中, 由飞秒激光超高功率密度所致的金属-空气混合等离子体使光束沿传播方向上发生散射, 发散角在6°~10°之间。热影响区的存在和混合等离子体的行为是影响飞秒激光烧蚀0Cr18Ni9不锈钢精度的主要因素。

The 0Cr18Ni9 stainless steel sheet was cut and drilled by a femtosecond laser, and the influence factors of machining accuracy of femtosecond laser ablation were studied.The morphology of stainless steel ablation zone and metallographic structure of cutting seam were examined by means of Nikon SMZ800 optical microscope and 4XC optical metallographic microscope. Based on the laser speckle on the surface of stainless steel observed by a coaxial CCD in the process of stainless steel ablation, the laser beam divergent propagation behavior was simulated using COMSOL Multiphysic numerical simulation software, and the beam divergence angle was calculated. Experimental and simulation results demonstrate that when the laser repetition rate is 5 kHz, the edge of cutting seam and hole are obviously blackened; metallographic phase shows that grain size significantly gets larger at cutting seam and heat affected zone can’t be avoided in the femtosecond laser ablation process; metal-air hybrid plasma induced by ultra-high power density femtosecond laser makes the laser beam scatter along the direction of propagation in the process of machining, the divergence angle is between 6° to 10°. The existence of heat affected zone and the behavior of the metal-air hybrid plasma are the main factors influencing the precision of femtosecond laser ablation.