镍基单晶材料皮秒级超短脉冲激光气膜孔加工表面完整性研究
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摘要
利用皮秒超短脉冲激光加工镍基单晶材料气膜孔,采用物理超景深显微镜对气膜孔成型几何形貌进行判定,采用金相显微镜对气膜孔内腔表面组织进行观测,采用高温低周疲劳设备对皮秒超短脉冲激光和电火花两种工艺加工出的气膜孔试样进行性能对比验证,采用扫描电镜对性能试样断口进行分析。结果表明:采用皮秒超短脉冲激光分步加工气膜孔,通过有效控制能量密度,可实现气膜孔进出口表面无烧蚀,几何精度满足设计指标,内腔无重熔层、断续小珠、起弧及微裂纹等缺陷,有效提升了气膜孔加工的表面完整性;通过皮秒超短脉冲激光及电火花气膜孔加工试样高温低周疲劳性能对比试验,皮秒超短脉冲激光制孔试样循环次数是电火花制孔试样的3倍;通过对两种工艺制孔高温低周疲劳断裂后试样进行扫描电镜断口分析,两种工艺加工试样断裂均为解理断裂,无材质冶金缺陷,电火花打孔形成的重熔层可能对断裂有贡献,超短脉冲激光打孔未见明显重熔层。
Aiming at the film cooling holes machining of nickel-based single crystal material by picosecond ultrashort pulsed laser, physical depth of field microscope is used to determine the geometry of the film cooling holes, meanwhile the cavity lumen surface of the membrane pore is observed by optical microscopy. Performances of porous film samples prepared by two processes of picosecond ultrashort pulsed laser and electric discharge using high temperature and low cycle fatigue equipment are compared, and specimen fracture is analyzed by scanning electron microscope(SEM) to evaluate the performance. The results show that the entering and exiting holes surface can avoid ablation by picosecond ultrashort pulsed laser processing step by step and effective control of energy density. While the geometric accuracy can meet the design specifications, also there is no remelting layer, intermittent beads,arcing and micro-cracks and other defects in the cavity. Besides, the surface integrity of the film holes after processing could be effectively improved. The comparative tests of high temperature low cycle fatigue performance of picosecond ultrashort pulsed and EDM film show that the cycle number of sample perforated by picosecond ultrashort pulsed laser is as many as three times that of EDM. SEM of high temperature low cycle fatigue fracture shows that the two kinds of processing specimens are cleavage fracture, without metallurgical defect, the remelting layer formed by EDM drilling may contribute to the fracture, and there is no obvious remelting layer in ultrashort pulsed laser drilling.
Aiming at the film cooling holes machining of nickel-based single crystal material by picosecond ultrashort pulsed laser, physical depth of field microscope is used to determine the geometry of the film cooling holes, meanwhile the cavity lumen surface of the membrane pore is observed by optical microscopy. Performances of porous film samples prepared by two processes of picosecond ultrashort pulsed laser and electric discharge using high temperature and low cycle fatigue equipment are compared, and specimen fracture is analyzed by scanning electron microscope(SEM) to evaluate the performance. The results show that the entering and exiting holes surface can avoid ablation by picosecond ultrashort pulsed laser processing step by step and effective control of energy density. While the geometric accuracy can meet the design specifications, also there is no remelting layer, intermittent beads,arcing and micro-cracks and other defects in the cavity. Besides, the surface integrity of the film holes after processing could be effectively improved. The comparative tests of high temperature low cycle fatigue performance of picosecond ultrashort pulsed and EDM film show that the cycle number of sample perforated by picosecond ultrashort pulsed laser is as many as three times that of EDM. SEM of high temperature low cycle fatigue fracture shows that the two kinds of processing specimens are cleavage fracture, without metallurgical defect, the remelting layer formed by EDM drilling may contribute to the fracture, and there is no obvious remelting layer in ultrashort pulsed laser drilling.
引文
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[3]CHICHKOV B N,MOMMA C,NOLTE S,et al.Femtosecond,picosecond and nanosecond laser ablation of solids[J].Applied Physics A,1996,63(2):109-115.
[4]LOPEZ J,TORRES R,ZAOUTER Y,et al.Study on the influence of repetition rate and pulse duration on ablation efficiency using a new generation of high power Ytterbium doped fiber ultrafast laser[J].Applied Surface Science,2013,283:1012–1017.
[5]NEUENSCHWANDER B,JAEGGI B,SCHMID M.From ps to fs:Dependence of the material removal rate and the surface quality on the pulse duration for metals,semiconductors and oxides[C]//ICALEO 2012 Presents the Latest in Laser Materials Processing Research.Anaheim,2012.