| Femtosecond laser has ultra-fast and ultra-powerful characteristics,femtosecond laser processing is suitable for many materials with high precision processing result and small thermal effect.Nanosecond laser has characteristics of high output power,stable operation and high removal efficiency.Laser precision processing is widely used in information and communication,aerospace,medical and other fields with a rapid development of laser technology.In this dissertation,by considering the characteristics of femtosecond laser and nanosecond laser,a systematic study has been carried out on fabricating high-quality periodic nanostructures on ITO films and processing film cooling holes in turbine blades.The main research results are as follows:1.By using a femtosecond laser with a central wavelength of 1030 nm and a pulse width of190 fs focused by a cylindrical lens,large-area and regular low-spatial-frequency laser-induced periodic surface structures(LSFL)with a period of 929±5 nm have been fabricated on the surface of ITO film by direct laser writing.First,the effect of different laser parameters on the surface morphology of ITO film has been investigated,regular LSFL can be fabricated with proper laser fluences and scanning velocities.Second,sheet resistances along the direction perpendicular to and parallel to the LSFL on ITO films have been measured by a four-probe measurement system,an anisotropic conductivity of ITO film has been achieved.Third,resistivity of individual LSFL(nanowire)has been measured by a dual-probe measurement system and element compositions of laser-irradiated ITO film have been analyzed,the results proved that direct laser writing did not affect the resistivity of ITO film.Finally,transmittance of ITO film to the infrared band can be improved by direct femtosecond laser writing,which is beneficial for applications of ITO films such as solar cells,display devices and organic light-emitting devices.2.A novel pulse-train generation method based on a frequency-doubled Fabry–Perot cavity has been developed.The time interval(60–1000 ps)and attenuation ratio(0.9–0.5)between adjacent sub-pulses of 515 nm pulse train can be easily adjusted,especially if the efficiency is up to 50%and remains unchanged.Extremely high-quality LSFL was efficiently fabricated on an ITO film using a pulse train with a time interval of 150 ps and attenuation ratio of 0.9 focused with a cylindrical lens.Compared with the LSFL induced by the primary Gaussian pulse,the uniformity of the LSFL period was enhanced from 481±41 nm to 435±8 nm;the divergence of structural orientation angle was reduced from 15.58°to 3.69°,and the depth was enhanced from 74.21±14.35 nm to 150.6±8.63 nm.The average line-edge roughness and line-height roughness are only 7.34 nm and 2.06 nm,respectively.Compared with a common Fabry–Perot cavity,the laser energy efficiency of the pulse trains and manufacturing efficiency are enhanced by factors of 19 and 25.A very colorful“lotus”pattern with a size of 30×28 mm~2 is demonstrated,which is covered with high-quality LSFLs fabricated by a pulse train with optimized laser parameters.By investigating the plasma-excitation process with a charge coupled device and a streak camera,it was found that pulse trains can efficiently enhance and prolong the excitation of surface plasmon polaritons,inhibit deposition particles,depress ablation residual heat and thermal shock waves,and eliminate high-spatial-frequency laser-induced periodic surface structures formed on LSFL,therefore,producing extremely high-quality LSFL on ITO film.3.By considering the high efficiency characteristic of nanosecond lasers and the high precision characteristic of femtosecond lasers,based on the cradle-type high-precision five-axis translation stages,a laser processing equipment for cooling holes of commercial aero-engine turbine blades has been developed,consisting of a four-light wedge processing module,a coaxial monitoring module,an on-line detection module and space attitude adjustment module.Works have been accomplished as follows.(1)Laser processing technology of nanosecond-femtosecond lasers for cooling holes in metal plates has been investigated,and laser processing of circular and fan-shaped cooling holes with different inclination angles on stainless steel plates have been accomplished.(2)Laser processing of circular and fan-shaped cooling holes with different inclination angles have been accomplished on the ceramic matrix composite plate with and without thermal barrier coating.(3)Key issues such as clamping,positioning,complex spatial attitude transformation,and online measurement in process of turbine blade cooling hole processing have been investigated,and 81cooling holes have been processed in a 3D printed stainless steel turbine blade.(4)Surface profile of the cooling hole has been analyzed by online detection,internal channel of the cooling hole has been detected by an industrial plug gauge,hole shape and inner wall quality have been analyzed by cutting the cooling hole,and full view of film cooling hole has been analyzed via industrial computerized tomography.The measurement results showed that aperture error of the cooling holes was less than 30μm,thickness of the recast layer and microcracks was lower than industrial error standard,positioning accuracy of the cooling holes in turbine blade was less than 100μm,and holes did not intersect. |
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