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| 3. |
- Bostanjoglo, Georg, et al.
(författare)
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Processing of Ni-based aero engine components with repetitively Q-switched Nd:YAG lasers
- 1996
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Ingår i: High-Power Lasers. - : SPIE. ; , s. 145-157
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Konferensbidrag (refereegranskat)abstract
- Aircraft engine industry uses free running high power Nd:YAG lasers for drilling cooling holes into nickel base alloy turbine components. A cw-pumped, Q-switched, high beam quality laser system with 400W laser power is presented. The laser is used to trepan drilling of 1.6mm. Hastelloy X sheets and ceramic coated combustion chamber tubes of the same metal. Cylindrical shape, uniformity, and reproducibility are achieved with a trepan-like drilling setup. The heat load of the workpiece as well as the process time is considerably decreased by employing high-repetition Q-switched lasers.
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| 4. |
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| 5. |
- Fällström, Karl-Evert, et al.
(författare)
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Generating and recording transient bending waves in plates by pulsed lasers
- 1996
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Ingår i: Experimental techniques (Westport, Conn.). - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 20:1, s. 15-19
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Tidskriftsartikel (refereegranskat)abstract
- We have presented a method to generate bending waves in a plate by focusing a Q-switched Nd:YAG-laser pulse on its surface. These waves are recorded by double pulsed hologram interferometry. Evaluation of the interferograms show that the bending wave pattern is very similar to what is predicted by the Kirchhoff plate equation assuming a point impact of infinitesimally short duration. This indicates that a short Nd:YAG-laser pulse may be considered as a Dirac pulse in space and time. Future investigations will be performed with a more powerful and "cleaner" laser to get a higher energy and impulse transfer to the plate thus giving bending waves of larger amplitude. Promising preliminary experiments have also begun using a double pulsed ruby laser both for generating and recording of bending waves.
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| 6. |
- Koh, Yangsook, et al.
(författare)
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Cleaning of corroded iron artefacts using pulsed TEA CO2- and Nd:YAG-lasers
- 2003
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Ingår i: Journal of Cultural Heritage. - 1296-2074 .- 1778-3674. ; 4:Suppl. 1, s. 129-133
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Tidskriftsartikel (refereegranskat)abstract
- Archaeological iron artefacts are often covered with a crust, containing organic fibres, mineral particles, dirt, etc. Before conservation, this crust must be carefully removed. With traditional mechanical and chemical methods, there is an obvious risk of over-cleaning. These methods also increase the risk of the oxidised or primary corrosion layer breaking away which will lead to loss of information about the form of the object and other important surface details. The main advantage of using pulsed lasers for cleaning metallic archaeological artefacts is that the removal of the crust is well controlled and can be carried out layer by layer. To determine the most suitable irradiation conditions, the wavelengths and the fluence for successful cleaning must be evaluated carefully. As test samples, corroded utility articles such as nails and hand tools have been used. Depending on the composition of the crust, different lasers have been used: TEA CO2 lasers have been successfully used for removal of organic materials and rust. EO-Q-switched Nd:YAG laser at IR and at green wavelengths, which have different absorption characteristics, has also been tested. The Nd:YAG laser was able to clean the corroded samples; however, the risk of surface damage was higher than when using the TEA CO2 laser. Analysis of the surfaces cleaned by lasers has been performed with optical and scanning electron microscopy, X-ray spectrometry and Raman-spectrometry
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| 7. |
- Koh, Yangsook, et al.
(författare)
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Removal of adhesives and coatings on iron artifacts using pulsed TEA CO2 and Nd:YAG lasers
- 2001
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Ingår i: Laser Techniques and Systems in Art Conservation. - Bellingham, wash. : SPIE - International Society for Optical Engineering. - 9780819440976 ; , s. 46-53
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Konferensbidrag (refereegranskat)abstract
- Selective and precise removal of surface coatings and contaminants can be achieved using lasers with a suitable wavelength. In this study pulsed TEA CO2- and Nd:YAG- lasers have been used to remove old adhesive and coatings from iron artifacts. This laser cleaning technique can enable extremely precise removal of old coating layers without damaging the underlying metal. Cleaning test on different samples using an Nd:YAG-laser with wavelengths of 1,064 nm, 532 nm and a TEA CO2-laser with 10,600 nm have been carried out. Trial sample were treated with different kinds of adhesive and coatings used in metal conservation and then cleaned using the three lasers. The results were compared with a conventional technique, micro blasting. Comparison of the laser cleaned surfaces was performed by optical microscopy and Raman-spectroscopy. The comparative study showed that the best results were achieved with the TEA CO2 laser, with the coatings being removed entirely without damage to the substrate. The original surface of the substrate was preserved and any re-deposited particles could be removed easily using a scalpel or brush after the laser radiation treatment.
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| 8. |
- Koh, Yang Sook, et al.
(författare)
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Surface cleaning of iron artefacts by lasers
- 2005
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Ingår i: Lasers in the Conservation of Artworks. - Berlin : Encyclopedia of Global Archaeology/Springer Verlag. - 9783540229964 ; , s. 95-100
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Konferensbidrag (refereegranskat)abstract
- In this paper the general method and ethics of the laser cleaning technique for conservation are presented. The results of two experiments are also presented; experiment 1 compares cleaning of rust by an Nd:YAG laser and micro-blasting whilst experiment 2 deals with removing the wax coating from iron samples by a TEA CO2 laser. The first experiment showed that cleaning with a pulsed laser and higher photon energy obtained a better surface structure than micro blasting. The second experiment showed how differences in energy density affect the same surface.
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| 9. |
- Meijer, J., et al.
(författare)
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Phase transformations by high-intensity sub-microsecond laser pulses.
- 1992
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Ingår i: Proceedings of the laser materials processing symposium, ICALEO '92. - Orlando, Fla : Laser institute of America. - 0912035498 ; , s. 228-236
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Konferensbidrag (refereegranskat)abstract
- In certain alloys, the 'laser shocking' causes work hardening, an increase in dislocation density and phase transformations. Of the materials tested, and austenitic Hadfield manganese-alloyed steel target was found to have the strongest tendency for a martensitic phase transformation. In contrast with conventional transformation hardening, there is no tempering in the case of repeated application. Whilst most material is vaporized, some surface melting will occur. The rate of re-solidification of the molten material is such that an almost completely amorphous structure results. The martensitic transformation has been confirmed by using optical, scanning and transmission electron microscopy, OM, SEM and TEM/STEM. Two different lasers, a Q-switched Ruby and a Q-switched Nd:YAG were used for the experiments. Calculations of impact/momentum, peak pressure and peak temperature were performed using the finite difference method. The model used for simulating the process has been proved to be useful in understanding the transformation mechanism.
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| 10. |
- Miroshnikova, Natalia, et al.
(författare)
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Percussion hole drilling of metals with a fourth-harmonic Nd:YAG laser studied by defocused laser speckle correlation
- 2005
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 44:17, s. 3403-3408
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Tidskriftsartikel (refereegranskat)abstract
- Defocused speckle correlation is introduced as a tool for measuring the response in metal sheets during percussion laser drilling. For this procedure the fourth-harmonic Nd:YAG wavelength (266 nm) was used in pulsed mode. The method provides a cost-efficient and robust alternative to speckle interferometry for the study of the small deformations that appear during laser processing. The accuracy was shown to be of the order of a few tens of microradians for the tilt component that is measured, which translates to a few nanometers in deflection when the component is spatially integrated. In the measurements, deflections in the form of craters as large as 50 nm were detected on the back sides of silver and copper sheets. The diameters of the craters were 300 μm in the silver and 150 μm in the copper sheet; the output diameter of the hole was ~5 μm.
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