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Étude de l'endommagement d'un superalliage monocristallin à base de nickel induit par microperçage laser milliseconde

Abstract : Improving the performance of an aircraft engine can be related to the rise in the combustion temperature. Progress of the aviation industry over the past 30 years has lead to this temperature increase. Turbine blades have seen their metallurgy and geometry evolve with time. Nowadays, they are made of a monocrystalline nickel-based superalloy. Thermal Barrier Coatings (TBCs), consist of a metallic bond-coat topped with a ceramic layer to protect the blade surface from temperature and aggressive environment (oxidation, high-temperature corrosion). In the same time of this material evolution, the geometry of the blade also changed. A cooling system allows heat evacuation due to internal circulation of air in a cooling network which is expulsed through micro-holes drilled at the blade surface. For many years, these holes (of 0,45mm in diameter and of between 1,5 and 3 mm in depth) have been drilled by pulsed laser or electrical discharge machining.
This work focuses on millisecond laser drilling which heat the irradiated material, melt it till the vaporization of the very surface layer of liquid. The resulting pressure, called recoil pressure, is the driving force for drilling. The objective of this study is to define and characterize the material damage induced by laser drilling. Finite element modelling of matter ejection phenomena was studied using a code which was developed formerly for laser welding. This model is compared with experimental measurements of liquid ejection speed and of recoil pressure. Additional micrographic observations have showed a resolidified layer of matter with a new microstructure. Current numerical models which are used to predict lifetime of drilled component involve only the stress gradient due to holes. High-temperature fatigue tests of specimens which were laser-drilled either using a millisecond laser or a femtosecond laser, allow to highlight the influence of the material modification induced by drilling on the mechanical behaviour. The study of the crack velocity combined to fractography leads to the understanding of short crack initiation and propagation mechanisms. It shows that the current craze for ultra-short pulsed laser sources (i.e. pico/femtosecond sources), which does not modify the microstructure of the hole as a conventional laser (millisecond) can do, is not justified for this type of application.
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https://pastel.archives-ouvertes.fr/pastel-00589345
Contributor : Bibliothèque Mines Paristech <>
Submitted on : Friday, April 29, 2011 - 9:56:23 AM
Last modification on : Wednesday, October 14, 2020 - 3:52:40 AM
Long-term archiving on: : Thursday, March 30, 2017 - 9:57:03 AM

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  • HAL Id : pastel-00589345, version 1

Citation

Nicolas Revuz. Étude de l'endommagement d'un superalliage monocristallin à base de nickel induit par microperçage laser milliseconde. Matériaux. École Nationale Supérieure des Mines de Paris, 2010. Français. ⟨NNT : 2010ENMP0047⟩. ⟨pastel-00589345⟩

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