基于飞秒激光的氧化硅纤维陶瓷加工研究

发布时间：2018-07-04 23:50

本文选题：飞秒激光 + 氧化硅纤维陶瓷　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：氧化硅纤维陶瓷是种新型超硬复合材料,其在军工和民用产业上均有着广泛的应用,但国内外对这种材料的加工工艺与加工机理均尚无进行系统的研究工作,所以对其进行加工研究具有重大的意义。氧化硅纤维具有硬度大、强度高的特点,使用传统加工方法存在设备老化严重、不能满足精度要求等缺点。针对以上问题,本文展开了针对氧化硅纤维的加工工艺与加工机理研究。本文在实验室的飞秒激光微加工系统的基础上,利用面积推算法获得了氧化硅纤维的飞秒激光破坏阈值,并辅以对蓝宝石材料的阈值测量,获得了破坏阈值与晶格结构的关系;同时得到了烧蚀阈值能量密度随脉冲个数的变化关系,并对变化原因进行了分析。结果表明蓝宝石的破坏阈值高于氧化硅纤维的,即飞秒激光微加工适用于氧化硅纤维陶瓷;材料中原子之间的作用力越强,则破坏这种材料所需要的能量越大;激光对材料的破坏存在孵化效应,即前一个激光脉冲诱导的材料改性将在下一个脉冲持续期间发挥作用;激光辐照下氧化硅纤维孵化效应产生的原因是材料内部存在杂质,蓝宝石孵化效应的原因是存在晶格缺陷。本文利用光学显微镜和表面轮廓仪分析了加工方向、平均功率、加工速度、路径数目、激光偏振状态和重频等参数对氧化硅纤维陶瓷加工效果的影响,提出了加工参数的优选原则,并对微加工的参数进行了优选。结果表明垂直于纤维方向加工形貌优于沿着纤维方向加工,但沿着纤维方向加工出的沟槽垂直度较好,且单脉冲去除速率较大;随着平均功率的增加,去除速率增加,但热影响区增大,形貌变差;随着加工次数的增加,沟槽深度先增加后不变,沟槽的宽度变化不大;沟槽深度与加工速度呈反相关关系,加工速度对沟槽的宽度影响不大;当激光为圆偏振光时,加工形貌与材料去除速率不受运动方向的影响,当激光为线偏振光时,不同运动方向情况下材料去除速率与表面形貌均有差别;低重频激光热影响区小,但加工边缘质量差,高重频激光恰与其相反。本文收集了实验过程中产生的等离子体发射谱线,并将飞秒激光和纳秒激光加工过程中等离子谱线发射元素进行对比,分析了飞秒激光加工氧化硅纤维陶瓷超硬材料的机理,获得了加工过程中的电荷转移过程。结果表明在飞秒激光辐照下,材料中成键的电子通过多光子吸收达到激发态,使得共价键断裂,经电子退相和电子热平衡过程后,能量在材料表层几个纳米厚度的吸收层迅速累积,瞬时达到的温度远远超过材料的气化温度,最终发生等离子体喷射以实现材料去除,实现了飞秒激光的非热熔性加工。
[Abstract]:Silicon oxide fiber ceramic is a new type of superhard composite material, which is widely used in military industry and civil industry. However, there is no systematic research on the processing technology and mechanism of this material at home and abroad. So it is of great significance to study its processing. Silicon oxide fiber has the characteristics of high hardness and high strength. In view of the above problems, the processing technology and mechanism of silicon oxide fiber are studied in this paper. Based on the femtosecond laser micromachining system in laboratory, the femtosecond laser damage threshold of silicon oxide fiber is obtained by using the area calculation method, and the threshold value of sapphire material is measured, and the relationship between the damage threshold and the lattice structure is obtained. At the same time, the relation of the energy density of ablation threshold with the number of pulses is obtained, and the reason of the change is analyzed. The results show that the destruction threshold of sapphire is higher than that of silica fiber, that is, femtosecond laser micromachining is suitable for silicon oxide fiber ceramics, the stronger the interaction force between atoms in the material, the greater the energy required to destroy the material. The destruction of materials by laser has hatching effect, that is, the material modification induced by the previous laser pulse will play a role in the duration of the next pulse, and the hatching effect of silicon oxide fiber under laser irradiation is due to the presence of impurities inside the material. The reason for the hatching effect of sapphire is lattice defect. In this paper, the effects of processing direction, average power, machining speed, path number, laser polarization state and repetition frequency on the machining effect of silicon oxide fiber ceramics are analyzed by means of optical microscope and surface profilometer. The principle of selecting machining parameters is put forward, and the parameters of micromachining are optimized. The results show that the perpendicular to the fiber direction is superior to the processing along the fiber direction, but the perpendicularity of the grooves processed along the fiber direction is better, and the removal rate of the single pulse is larger, and the removal rate increases with the increase of the average power. With the increase of processing times, the groove depth increases first and then remains unchanged, and the width of groove does not change much; the groove depth is inversely correlated with the machining speed, and the processing speed has little effect on the groove width. When the laser is circular polarized, the processing morphology and the material removal rate are not affected by the moving direction, when the laser is the linear polarized light, the material removal rate and the surface morphology are different in different moving directions, and the heat affected area of low repetition frequency laser is small. But the quality of machining edge is poor, high repetition frequency laser is exactly the opposite. In this paper, the plasma emission lines produced in the experiment are collected, and the mechanism of femtosecond laser processing of silicon oxide fiber ceramic superhard materials is analyzed by comparing the emission elements of plasma emission lines between femtosecond laser and nanosecond laser processing. The charge transfer process in the process was obtained. The results show that under femtosecond laser irradiation, the bonding electrons in the material reach the excited state through multi-photon absorption, which makes the covalent bond break, and after the electron dephase and the electron thermal equilibrium process, The energy accumulates rapidly in several nanometer-thickness absorption layers on the surface of the material, and the instantaneous temperature is far higher than the gasification temperature of the material. Finally, plasma jet occurs to realize the material removal, and the non-thermal melting processing of femtosecond laser is realized.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ174.6

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