【作者】 张丽丽；

【导师】 孙树峰；

【作者基本信息】 青岛理工大学 ， 机械工程， 2022， 硕士

【摘要】 涡轮叶片是航空发动机的核心零部件,它的工作环境极为恶劣,承受着高温高压燃气的冲击。镍基高温合金和碳化硅陶瓷基复合材料是涡轮叶片制造材料,在涡轮叶片上加工气膜孔实现气膜冷却。传统的加工技术在加工气膜孔时存在困难,无法实现高精度气膜孔的加工要求。激光加工技术是一种新型的制造技术,可以解决精密微纳加工的一系列问题。本研究尝试采用激光加工技术,探索激光加工气膜孔的工艺,旨在提高涡轮叶片气膜孔的加工质量。本论文针对涡轮叶片气膜孔开展以IN718镍基高温合金和SiC/SiC复合材料为研究对象,以激光加工技术作为加工手段,进行气膜孔加工。首先,分析了目前的气膜孔加工技术,并对激光加工技术和液体辅助激光加工技术的研究现状进行了总结。详细介绍了激光去除材料的作用机理和激光击穿液体的作用机理,并分析了激光在液体中的传输特性和聚焦特性、激光击穿液体对物质产生的冲击作用和空化作用及化学液对物质的腐蚀作用。进一步介绍了液体辅助激光加工的试验设备和试验原理。其次,针对IN718镍基高温合金进行了液体辅助纳秒激光加工微孔的试验研究。在空气中探究了同心圆填充、弓字填充和直线填充对加工方形孔、梯形孔和椭圆形孔的影响规律,结果表明:直线填充方式加工的微孔直径最小。将直线填充方式应用于圆形孔加工,发现随激光功率的增大孔直径增大,当激光功率在100W时,微孔的锥度为4.66°～5.26°。在水溶液中探究了离焦量和液层厚度对微孔加工的影响,得到最佳加工参数:离焦量为-100μm,液层厚度为1mm,并验证了溶液的冷却作用和冲击作用可以有效减少熔融物的堆积。在化学液中探究了扫描速度和扫描次数对微孔加工的影响,结果表明化学液的腐蚀作用加速了孔内熔融物质和残渣的溶解。当离焦量为-100μm,液层厚度为1mm,扫描速度为30mm/s,扫描次数为100次时,激光在水中微孔的锥度为3.95°～4.8°,入口圆度可达97%;激光在化学液中微孔的锥度为3.55°～4.29°,入口圆度可达97.7%。综上,液体辅助纳秒激光加工可以得到无重铸层,孔壁相对光滑的微孔,提高了微孔的质量。最后,针对SiC/SiC复合材料进行了液体辅助纳秒激光加工微孔的试验研究。在静态水溶液辅助纳秒激光多脉冲叩击打孔时,计算了材料的损伤阈值,研究了激光功率和脉冲数对孔烧蚀的影响,并与纳秒激光在空气中加工的结果进行对比。结果表明:激光在水中加工SiC/SiC复合材料的损伤阈值小于空气中,激光在水中的烧蚀效率更高。在静态水溶液辅助纳秒激光环切加工时,研究了液层厚度和激光功率对微孔加工的影响,结果表明:当液层厚度为0.5mm,激光功率为120W时,微孔的锥度为3.72°～4.47°;纳秒激光在空气中加工SiC/SiC复合材料时,复合材料发生燃烧现象,在水中加工可以避免其发生燃烧。然而,静态水溶液产生的冲击力无法将激光加工产生的缺陷层完全去除。为了去除纳秒激光加工SiC/SiC复合材料生成的重铸层和氧化层等缺陷层,提高激光加工微孔的质量和效率,提出动态溶液辅助纳秒激光加工技术,并探究了动态水溶液和动态化学液辅助激光加工微孔的作用机理。通过分析SiC/SiC复合材料的元素组成和化学性质,筛选并配置出2mol/L HF和3mol/L HNO₃的混合溶液,使其满足在常温下不与材料发生反应,在高温下与激光加工产生的缺陷层发生反应。研究了动态溶液辅助激光加工中喷出溶液与加工表面的距离、喷出溶液流量和激光功率对微孔加工的影响,结果得到:当喷出溶液与加工表面距离为4mm,喷出溶液流量为15L/h,激光功率为100W时,在水溶液中微孔的锥度为4.28°,在化学液中微孔的锥度为3.99°。相对比,动态溶液辅助激光加工技术利用动态射流产生的冲击力和化学溶液的腐蚀作用有效去除了激光加工中产生的重铸层和氧化层,获得无重铸层和氧化层的微孔。本文系统的研究了液体辅助纳秒激光加工气膜孔的作用机理及工艺参数对微孔加工的影响,对涡轮叶片气膜孔的加工技术具有一定的理论和试验参考价值,为后续实际的工业生产提供理论和实践支撑。更多还原

【Abstract】 Turbine blade is the core component of aeroengine.It bears the impact of high temperature and high pressure gas.The working environment of turbine blade is extremely harsh.Nickel-based superalloys and silicon carbide ceramic matrix composites are the turbine blade manufacturing materials.Film cooling is achieved by processing film holes on the turbine blades.The traditional processing technology is difficult to process the film hole and can not achieve the high precision of the film hole processing requirements.Laser processing technology is a new manufacturing technology,which can solve a series of problems in precision micro-nano processing.This study attempts to use laser processing technology to explore the process of laser processing film holes,aiming to improve the quality of turbine blade film holes.In this paper,IN718 nickel-based superalloys and SiC/SiC composites are used as research objects,and laser processing technology is used as processing method to process film holes in turbine blades.Firstly,the current film hole processing technology is analyzed.The research status of laser processing technology and liquid assisted laser processing technology is summarized.The processing mechanism of laser removal materials and the processing mechanism laser breakdown liquid are introduced.The transmission and focusing characteristics of laser in liquid,the impact and cavitation effect of laser breakdown liquid on materials,and the corrosion effect of chemical solution on materials are analyzed.The experimental equipment and experimental principle of liquid assisted laser processing are further introduced.Secondly,the liquid assisted nanosecond laser processing of IN718 nickel-based superalloys was studied.In air,the effects of concentric circle filling,arch filling and linear filling on square holes,trapezoidal holes and elliptical holes were investigated.The results show that the microholes diameter processed by linear filling is the smallest.The linear filling method was applied to the processing of circular holes.The microholes diameter increased with the increase of laser power.When the laser power is100W,the microholes taper is 4.66°～5.26°.In water solution,the influence of defocus distance and liquid layer thickness on microholes processing were investigated.The optimal processing parameters were obtained:the defocus distance is-100μm,the liquid layer thickness is 1mm.And it is verified that the cooling and impact effects of the water solution can effectively reduce the accumulation of molten materials.In chemical solution,the effects of scanning speed and scanning times on microholes processing were investigated.The results show that the corrosion effect of chemical solution accelerates the dissolution of molten materials and residues in the holes.When the defocus distance is-100μm,the liquid layer thickness is 1mm,the scanning speed is30mm/s and the scanning times is 100,the microholes taper in water is 3.95°～4.8°,and the inlet roundness reaches 97%.The microholes taper in chemical solution is3.55°～4.29°,and the inlet roundness reaches 97.7%.In conclusion,liquid assisted nanosecond laser processing can obtain microholes without recasting layer and relatively smooth hole wall,which improves the microholes quality.Finally,the liquid assisted nanosecond laser processing of SiC/SiC composites was studied.In static water solution assisted nanosecond laser multi-pulse percussion drilling,the damage threshold of composites was calculated and the effects of laser power and pulse number on the hole ablation were studied.The results show that the damage threshold of SiC/SiC composites processed by laser in water is lower than that in air.The laser ablation in water is more efficient.In static water solution assisted nanosecond laser trepanning drilling,the effects of liquid layer thickness and laser power on microholes processing were studied.The result show that when the liquid layer thickness is 0.5mm,the laser power is 120W,the microholes taper is 3.72°～4.47°.When nanosecond laser is processed in air,SiC/SiC composites burn.The composites can avoid burning when laser is processed in water.However,the impact force generated by static water solution cannot completely remove the defect layer produced by laser processing.In order to remove the recast layer and oxide layer generated by nanosecond laser processing SiC/SiC composites,the dynamic solution assisted laser processing technology was proposed.The processing mechanism of dynamic water solution and dynamic chemical solution assisted laser processing was investigated.By analyzing the elements composition and chemical properties of SiC/SiC composites,the mixed solution of 2mol/L HF and 3mol/L HNO₃was selected and configured.The mixed solution satisfies that it could not react with the composites at room temperature,but react with the defect layer produced by laser processing at high temperature.In dynamic solution assisted laser processing,the effects of the distance between ejection solution and processing surface,ejection solution flow rate and laser power on the microholes processing were studied.The results show that when the distance between ejection solution and processing surface is 4mm,the ejection solution flow rate is 15L/h,and the laser power is 100W,the microholes taper in water solution is 4.28°,and the microholes taper in chemical solution is 3.99°.Using the impact force generated by dynamic jet and the corrosion effect of chemical solution,the dynamic solution assisted laser processing technology effectively removes the recast layer and oxide layer generated in laser processing,and obtains microholes without defect layers.This paper systematically studies the mechanism of liquid assisted nanosecond laser processing of film holes and the influence of process parameters on microholes processing.It has certain theoretical and experimental value for turbine film hole processing technology.This also provides theoretical and practical support for subsequent practical industrial production.更多还原