本文選題：高溫合金 + 毫秒激光　； 參考：《江蘇大學(xué)》2017年碩士論文

【摘要】：相對(duì)于傳統(tǒng)微孔加工方法,激光打孔技術(shù)以其獨(dú)特的優(yōu)勢(shì)在制造業(yè)得到廣泛應(yīng)用,尤其是在航空航天、電子、汽車和生物醫(yī)學(xué)等領(lǐng)域。毫秒激光因其功率大、加工效率高、精度可控等優(yōu)點(diǎn)成為航空航天微孔加工領(lǐng)域最重要的打孔工具之一。本文以航空發(fā)動(dòng)機(jī)熱端部件冷卻氣膜孔加工為研究背景,首先綜述了微小孔在航空發(fā)動(dòng)機(jī)中的應(yīng)用和氣膜冷卻孔的重要意義,在此基礎(chǔ)上介紹了國內(nèi)外激光加工氣膜孔的研究現(xiàn)狀,以及數(shù)值模擬技術(shù)在激光打孔過程中的應(yīng)用。在總結(jié)出毫秒激光打孔過程存在的不足的基礎(chǔ)上,對(duì)毫秒激光打孔過程進(jìn)行了實(shí)驗(yàn)和數(shù)值模擬研究。論文以航空發(fā)動(dòng)機(jī)熱端部件常用的制造材料GH4169為對(duì)象進(jìn)行實(shí)驗(yàn),使用單因素法分別研究了激光脈沖能量、頻率、脈寬、離焦量、擴(kuò)束比、脈沖個(gè)數(shù)等參數(shù)對(duì)微孔入、出口表面形貌、孔徑和錐度的影響規(guī)律。實(shí)驗(yàn)表明:平均功率、頻率和脈寬通過間接改變激光能量密度的方式影響微孔形貌。離焦量和擴(kuò)束比實(shí)際是通過改變激光的聚焦?fàn)顟B(tài)對(duì)打孔效果產(chǎn)生影響,離焦量對(duì)孔徑影響較大,擴(kuò)束比對(duì)孔錐度影響較大。多個(gè)脈沖的連續(xù)沖擊,能反復(fù)修整孔形,實(shí)現(xiàn)微孔徑、錐度和深徑比的控制;由于毫秒激光高功率和長脈寬的特點(diǎn),加工出的微孔周圍普遍存在熔融堆積的現(xiàn)象。通過對(duì)實(shí)驗(yàn)結(jié)果的分析,歸納出GH4169高溫合金毫秒激光沖擊打孔最優(yōu)化加工參數(shù),即:平均功率90W,脈沖寬度1ms,重復(fù)頻率30Hz,離焦量0mm,擴(kuò)束比4,輔助氣體為N2或Ar,氣壓為4Bar。在實(shí)驗(yàn)基礎(chǔ)上,檢測(cè)并分析了毫秒激光熱效應(yīng)對(duì)激光燒蝕區(qū)和熱影響區(qū)的金相組織和元素成分分布的影響。發(fā)現(xiàn)距離孔邊緣大約200μm范圍內(nèi),晶粒尺寸明顯變大,隨著激光熱影響范圍從孔邊緣向基體延伸,晶粒逐漸減小并接近基體組織�？變�(nèi)較小的過冷環(huán)境使孔內(nèi)殘留熔融金屬凝固時(shí)晶粒異常長大,使控制GH4169合金缺口敏感性的δ相的形核界面減少,導(dǎo)致δ相生成量降低,最終重鑄層呈現(xiàn)出缺口敏感性。熱效應(yīng)在熱影響區(qū)內(nèi)產(chǎn)生近似固溶和時(shí)效處理的效果,組織中的主要強(qiáng)化相??在高溫條件下發(fā)生異化轉(zhuǎn)化,降低了該區(qū)域合金的機(jī)械強(qiáng)度。元素檢測(cè)結(jié)果顯示,熱影響區(qū)和激光燒蝕區(qū)中的Ni、Fe、Cr、Nb、Al、Si等主要元素含量明顯減少,而O、Si等元素含量明顯增加,削弱了元素對(duì)合金的強(qiáng)化作用,降低了合金組織和性能的穩(wěn)定性。此外,還對(duì)毫秒激光打孔過程中出現(xiàn)的缺陷如孔內(nèi)微裂紋、孔周圍飛濺物堆積等進(jìn)行了研究,發(fā)現(xiàn)使用氮?dú)�、氬氣等惰性氣體作輔助氣體可以明顯降低孔內(nèi)壁微裂紋的形成。在加工表面鍍有機(jī)涂層的方法可以大大減少飛濺物堆積對(duì)加工面的損傷。為驗(yàn)證實(shí)驗(yàn)規(guī)律的可靠性,論文同時(shí)對(duì)高溫合金毫秒激光打孔進(jìn)行了數(shù)值模擬研究。將激光打孔簡化為二維對(duì)稱結(jié)構(gòu),建立了熱傳導(dǎo)溫度場分布數(shù)學(xué)模型,并分析了非線性瞬態(tài)傳熱問題和相變問題的處理方法。運(yùn)用ANSYS10.0有限元軟件和參數(shù)化設(shè)計(jì)語言對(duì)GH4169高溫合金毫秒激光打孔溫度場分布和孔輪廓形成過程進(jìn)行了數(shù)值模擬分析,得到不同脈沖個(gè)數(shù)下激光打孔溫度場分布云圖和輪廓形成圖。溫度場仿真結(jié)果表明:激光垂直照射材料時(shí),溫度場關(guān)于激光束軸線呈對(duì)稱分布,溫度從孔中心向邊界逐漸遞減,符合高斯光束的能量分布規(guī)律和打孔實(shí)際�？纵喞獔D呈現(xiàn)了隨著激光脈沖個(gè)數(shù)的增加孔輪廓形成的動(dòng)態(tài)過程。孔徑和孔深的模擬值和實(shí)驗(yàn)值保持相同的變化規(guī)律性�？紤]到打孔的復(fù)雜性,模型簡化了一些實(shí)際條件,使得模擬值比實(shí)驗(yàn)值偏大,但仍可以為實(shí)際生產(chǎn)提供規(guī)律性指導(dǎo)。
[Abstract]:Compared with the traditional microporous processing methods, laser drilling technology is widely used in the manufacturing industry because of its unique advantages, especially in the fields of aerospace, electronics, automobile and biomedicine. The millisecond laser has become one of the most important drilling tools in aeronautical Aerospace micromachining because of its high power, high processing efficiency and controllable precision. In this paper, the important significance of the application of micro holes in the aero engine and the important significance of the air film cooling holes in the aero engine hot end components are reviewed. On this basis, the current research status of the laser processing gas film holes at home and abroad, and the application of the numerical simulation technology in the process of laser drilling are summarized. On the basis of the shortcomings of the millisecond laser drilling process, the experiment and numerical simulation of the millisecond laser drilling process are carried out. The experiment is carried out by using the manufacturing material GH4169 commonly used in the hot end parts of the aero engine. The laser pulse energy, frequency, pulse width, defocus, expansion ratio, and pulse are studied by single factor method. The experimental results show that the average power, frequency and pulse width affect the micropore morphology by means of indirectly changing the laser energy density. The amount of defocus and the ratio of beam expansion are actually influenced by the change of the focusing state of the laser, and the effect of the defocus amount on the aperture is more than that of the laser. Large, beam expansion ratio has greater impact on the taper of the hole. The continuous impact of multiple pulses can be repeated to repair the hole shape to realize the control of the micro aperture, taper and depth diameter ratio. Due to the high power and long pulse width of the millisecond laser, the phenomenon of melting and accumulation around the micropores is generally existed. Through the analysis of the experimental results, the GH4169 superalloy is summed up. The optimum processing parameters of the millisecond laser percussion drilling are: the average power 90W, the pulse width 1ms, the repetition rate 30Hz, the defocusing 0mm, the beam expansion ratio 4, the auxiliary gas N2 or Ar, and the pressure of 4Bar. on the experiment basis, to detect and analyze the influence of the millisecond laser thermal effect on the metallographic structure and the element composition distribution of the laser ablation zone and the heat affected zone. It is found that the grain size is obviously larger in the range of about 200 m from the edge of the hole. With the laser heat influence extending from the edge of the hole to the matrix, the grain gradually decreases and is close to the matrix. The small supercooling environment in the hole makes the grain abnormal when the molten metal is solidified in the hole, making the nucleation of the delta phase controlling the sensitivity of the GH4169 alloy gap. The decrease of the interface leads to a decrease in the quantity of the delta phase, and the final recast layer presents the notch sensitivity. The effect of heat effect in the heat affected zone is similar to the effect of solid solution and aging treatment. The main strengthening phase in the tissue? Dissimilation transformation under high temperature conditions and the reduction of the mechanical strength of the alloy in this region. The result of the element detection shows that the heat affected zone and the excitation are stimulated. The contents of Ni, Fe, Cr, Nb, Al, Si and other major elements in the optical ablation zone are obviously reduced, while the content of O, Si and other elements is obviously increased, which weakens the strengthening effect of the elements to the alloy and reduces the stability of the microstructure and properties of the alloy. In addition, the defects in the millisecond laser drilling process, such as the micro cracks in the hole and the accumulation of spatter around the hole, are also carried out. It is found that the use of inert gases such as nitrogen and argon as auxiliary gas can obviously reduce the formation of micro cracks in the inner wall of the hole. The method of plating organic coating on the machined surface can greatly reduce the damage to the surface of the spatter. In order to verify the reliability of the experimental law, the numerical model of the millisecond laser drilling of the superalloy is also carried out in this paper. The laser drilling is simplified as a two-dimensional symmetric structure, a mathematical model of the heat conduction temperature field distribution is established, and the processing method of the nonlinear transient heat transfer and phase transition is analyzed. The temperature field distribution and the hole profile of the GH4169 millisecond laser drilling are formed by using the ANSYS10.0 finite element software and the parameterized design language. The simulation results show that the temperature field is symmetrical about the axis of the laser beam and the temperature decreases gradually from the center of the hole to the boundary, which conforms to the energy distribution law of the Gauss beam and the beating of the laser beam. The hole contour map presents the dynamic process of the formation of the hole contour with the number of laser pulses. The simulated values of the aperture and the hole depth have the same variation regularity. Considering the complexity of the perforation, the model simplifies some actual conditions and makes the simulation value larger than the experimental value, but it can still provide the rules for the actual production. Guidance of law.

【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG132.3;TG665

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