高温合金毫秒激光打孔实验与数值模拟研究

发布时间：2018-04-29 13:05

本文选题：高温合金 + 毫秒激光　；参考：《江苏大学》2017年硕士论文

【摘要】：相对于传统微孔加工方法,激光打孔技术以其独特的优势在制造业得到广泛应用,尤其是在航空航天、电子、汽车和生物医学等领域。毫秒激光因其功率大、加工效率高、精度可控等优点成为航空航天微孔加工领域最重要的打孔工具之一。本文以航空发动机热端部件冷却气膜孔加工为研究背景,首先综述了微小孔在航空发动机中的应用和气膜冷却孔的重要意义,在此基础上介绍了国内外激光加工气膜孔的研究现状,以及数值模拟技术在激光打孔过程中的应用。在总结出毫秒激光打孔过程存在的不足的基础上,对毫秒激光打孔过程进行了实验和数值模拟研究。论文以航空发动机热端部件常用的制造材料GH4169为对象进行实验,使用单因素法分别研究了激光脉冲能量、频率、脉宽、离焦量、扩束比、脉冲个数等参数对微孔入、出口表面形貌、孔径和锥度的影响规律。实验表明:平均功率、频率和脉宽通过间接改变激光能量密度的方式影响微孔形貌。离焦量和扩束比实际是通过改变激光的聚焦状态对打孔效果产生影响,离焦量对孔径影响较大,扩束比对孔锥度影响较大。多个脉冲的连续冲击,能反复修整孔形,实现微孔径、锥度和深径比的控制;由于毫秒激光高功率和长脉宽的特点,加工出的微孔周围普遍存在熔融堆积的现象。通过对实验结果的分析,归纳出GH4169高温合金毫秒激光冲击打孔最优化加工参数,即:平均功率90W,脉冲宽度1ms,重复频率30Hz,离焦量0mm,扩束比4,辅助气体为N2或Ar,气压为4Bar。在实验基础上,检测并分析了毫秒激光热效应对激光烧蚀区和热影响区的金相组织和元素成分分布的影响。发现距离孔边缘大约200μm范围内,晶粒尺寸明显变大,随着激光热影响范围从孔边缘向基体延伸,晶粒逐渐减小并接近基体组织。孔内较小的过冷环境使孔内残留熔融金属凝固时晶粒异常长大,使控制GH4169合金缺口敏感性的δ相的形核界面减少,导致δ相生成量降低,最终重铸层呈现出缺口敏感性。热效应在热影响区内产生近似固溶和时效处理的效果,组织中的主要强化相??在高温条件下发生异化转化,降低了该区域合金的机械强度。元素检测结果显示,热影响区和激光烧蚀区中的Ni、Fe、Cr、Nb、Al、Si等主要元素含量明显减少,而O、Si等元素含量明显增加,削弱了元素对合金的强化作用,降低了合金组织和性能的稳定性。此外,还对毫秒激光打孔过程中出现的缺陷如孔内微裂纹、孔周围飞溅物堆积等进行了研究,发现使用氮气、氩气等惰性气体作辅助气体可以明显降低孔内壁微裂纹的形成。在加工表面镀有机涂层的方法可以大大减少飞溅物堆积对加工面的损伤。为验证实验规律的可靠性,论文同时对高温合金毫秒激光打孔进行了数值模拟研究。将激光打孔简化为二维对称结构,建立了热传导温度场分布数学模型,并分析了非线性瞬态传热问题和相变问题的处理方法。运用ANSYS10.0有限元软件和参数化设计语言对GH4169高温合金毫秒激光打孔温度场分布和孔轮廓形成过程进行了数值模拟分析,得到不同脉冲个数下激光打孔温度场分布云图和轮廓形成图。温度场仿真结果表明:激光垂直照射材料时,温度场关于激光束轴线呈对称分布,温度从孔中心向边界逐渐递减,符合高斯光束的能量分布规律和打孔实际。孔轮廓图呈现了随着激光脉冲个数的增加孔轮廓形成的动态过程。孔径和孔深的模拟值和实验值保持相同的变化规律性。考虑到打孔的复杂性,模型简化了一些实际条件,使得模拟值比实验值偏大,但仍可以为实际生产提供规律性指导。
[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.

【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG132.3;TG665

【参考文献】