本文選題：飛秒激光 + 氧化硅纖維陶瓷��； 參考：《哈爾濱工業(yè)大學》2015年碩士論文

【摘要】：氧化硅纖維陶瓷是種新型超硬復合材料,其在軍工和民用產業(yè)上均有著廣泛的應用,但國內外對這種材料的加工工藝與加工機理均尚無進行系統(tǒng)的研究工作,所以對其進行加工研究具有重大的意義。氧化硅纖維具有硬度大、強度高的特點,使用傳統(tǒng)加工方法存在設備老化嚴重、不能滿足精度要求等缺點。針對以上問題,本文展開了針對氧化硅纖維的加工工藝與加工機理研究。本文在實驗室的飛秒激光微加工系統(tǒng)的基礎上,利用面積推算法獲得了氧化硅纖維的飛秒激光破壞閾值,并輔以對藍寶石材料的閾值測量,獲得了破壞閾值與晶格結構的關系;同時得到了燒蝕閾值能量密度隨脈沖個數的變化關系,并對變化原因進行了分析。結果表明藍寶石的破壞閾值高于氧化硅纖維的,即飛秒激光微加工適用于氧化硅纖維陶瓷;材料中原子之間的作用力越強,則破壞這種材料所需要的能量越大;激光對材料的破壞存在孵化效應,即前一個激光脈沖誘導的材料改性將在下一個脈沖持續(xù)期間發(fā)揮作用;激光輻照下氧化硅纖維孵化效應產生的原因是材料內部存在雜質,藍寶石孵化效應的原因是存在晶格缺陷。本文利用光學顯微鏡和表面輪廓儀分析了加工方向、平均功率、加工速度、路徑數目、激光偏振狀態(tài)和重頻等參數對氧化硅纖維陶瓷加工效果的影響,提出了加工參數的優(yōu)選原則,并對微加工的參數進行了優(yōu)選。結果表明垂直于纖維方向加工形貌優(yōu)于沿著纖維方向加工,但沿著纖維方向加工出的溝槽垂直度較好,且單脈沖去除速率較大;隨著平均功率的增加,去除速率增加,但熱影響區(qū)增大,形貌變差;隨著加工次數的增加,溝槽深度先增加后不變,溝槽的寬度變化不大;溝槽深度與加工速度呈反相關關系,加工速度對溝槽的寬度影響不大;當激光為圓偏振光時,加工形貌與材料去除速率不受運動方向的影響,當激光為線偏振光時,不同運動方向情況下材料去除速率與表面形貌均有差別;低重頻激光熱影響區(qū)小,但加工邊緣質量差,高重頻激光恰與其相反。本文收集了實驗過程中產生的等離子體發(fā)射譜線,并將飛秒激光和納秒激光加工過程中等離子譜線發(fā)射元素進行對比,分析了飛秒激光加工氧化硅纖維陶瓷超硬材料的機理,獲得了加工過程中的電荷轉移過程。結果表明在飛秒激光輻照下,材料中成鍵的電子通過多光子吸收達到激發(fā)態(tài),使得共價鍵斷裂,經電子退相和電子熱平衡過程后,能量在材料表層幾個納米厚度的吸收層迅速累積,瞬時達到的溫度遠遠超過材料的氣化溫度,最終發(fā)生等離子體噴射以實現(xiàn)材料去除,實現(xiàn)了飛秒激光的非熱熔性加工。
[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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ174.6

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