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Etude des mécanismes de corrosion de l'Inconel 617 dans le circuit primaire des Réacteurs à Haute Température refroidis par hélium

Abstract : Inconel 617 is an alloy containing nickel, chromia and molybdenum and is ranked as one of the candidate materials in the realization of heat exchangers of High Temperature Reactors (HTR) cooled by helium (reactors of generation IV). The experience feedback shows that helium contains gas impurities H2O, H2, CO, CH4 in reduced quantities (on the micro bar scale), responsible for reactions of oxidation, carburization or decarburization between 850°C and 1 000°C. The formation of a protective oxide layer is planned to avoid the degradation of the mechanical properties of the heat exchanger. Within the framework of the analysis of the processes of oxidation of Inconel, two research orientations are approached. One is centred on the influence of water vapour and carbon monoxide and the other on the role of the minor elements, notably, aluminium and titanium. The specific study on the role of aluminium and titanium calls upon the alloy model containing NiCrMoC. After having studied each of these parameters during 20 hours of tests at 850°C, the results are the following. The water vapour is responsible for more than 90 % of the oxidation of Inconel 617 and it inhibits in certain cases the reaction between carbon monoxide and alloy. The oxide layer formed contains chromine (Cr2O3) and is rich in titanium and manganese. We show that the doping of the chromine by titanium favours the formation of a protective oxide layer. As for the presence of alumina to the interface metal/oxide, we show that it slows down the growth rate of the oxide layer. According to the content of water vapour, the growth of the oxide layer of Inconel 617 is described either by a mixed kinetic mode of diffusion and interface (for PH2O ≤ 10 μbar), or by a pure mode of diffusion (for PH2O > 10 μbar). In both cases, the speed of consumption of carbon monoxide is modelled by a process of adsorption on the surface of the oxide layer. However, the integrity of the oxide layer is compromised during the rise of temperature. Beyond a critical temperature, noted TA, we observe the destruction of the oxide layer. We show that the reaction of destruction which proceeds at the interface metal/oxide brings into play the carbon of alloy and the chromine to produce chromium of which one part evaporates and carbon monoxide is released. On the basis of our result, we propose a kinetic model.
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  • HAL Id : tel-00992077, version 1

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Jérôme Chapovaloff. Etude des mécanismes de corrosion de l'Inconel 617 dans le circuit primaire des Réacteurs à Haute Température refroidis par hélium. Matériaux. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2009. Français. ⟨NNT : b2009EMSE0024⟩. ⟨tel-00992077⟩

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