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Etude de procédés de préparation de surface avant nitruration - fiabilité du procédé

Abstract : The gaseous nitriding of steel parts is a thermochemical process that generates a mechanical properties gradient at the surface by nitrogen diffusion. The treated parts indicate an important residual stress and hardness gradient, optimized for power transmission applications used in aeronautics and motor sports. The increase of nitrogen concentration is due to the catalytic decomposition of ammonia at the iron-based surface of parts. However, the process is extremely sensitive to the surface state of parts that includes geometrical, mechanical but also chemical properties. This state can inhibit the catalytic decomposition properties and the nitrogen diffusion. This deactivation can have different origins, such as the adsorption of a poisoning element or the fouling of the surface of the parts. The catalytic deactivation phenomenon is studied since decades. However, few publications are available in the case of its application in the specific case of the gaseous nitriding of steel. A better understanding of the nitriding inhibition would improve the reliability of this industrial process. In order to answer this demand, an experimental approach, based on industrial case and bibliographical study, is proposed. A pollution study obtained from machining oil residues, carbon deposit, or sulfur poisoning is proposed. Moreover, an experimental approach, aiming to determine the impact of initial mechanical properties on the nitriding process is proposed. Thermogravimetric analyses coupled to observations and mechanical properties analyses enable to develop the knowledge of the nitrided surfaces deactivation processes. After this study, the surface activation capacity of three in-situ processes, namely oxidation, urea and ammonium chloride, over the previously studied contaminations is determined.
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Submitted on : Wednesday, March 21, 2018 - 3:48:10 PM
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  • HAL Id : tel-01740076, version 1


Benjamin Guillot. Etude de procédés de préparation de surface avant nitruration - fiabilité du procédé. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2016. Français. ⟨NNT : 2016ENAM0068⟩. ⟨tel-01740076⟩



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