Chemical Evolution in the Substrate due to oxidation: A Numerical Model with Explicit Treatment of Vacancy Fluxes

To get a better understanding of oxidation behavior of Ni-base alloys in PWR primary water, a numerical model for oxide scale growth has been developed. The final aim of the model is to estimate the effects of possible changes of experimental conditions. Hence, our model has not been restricted by the classical hypothesis of quasi-steady state and can consider transient stages. The model calculates the chemical species concentration profiles, but also the vacancy concentration profiles evolution in the oxide and in the metal as a function of time. It treats the elimination of the possible supersaturated vacancies formed at the metal/oxide interface by introducing a dislocation density at the interface and in the metal bulk. This latter density can be related to the cold-working state. Its effect on the vacancy profile evolution is studied in the case of a pure metal. Eventually an extension of the present model to the oxidation of Ni-base alloys is discussed regarding a recent vacancy diffusion model adjusted on Ni-base alloys

Démarche utilisée par Creusot Forge pour l'amélioration des gammes de fabrication de ses pièces

Creusot Forge s'est tourné vers la simulation numérique afin d'améliorer et de développer ses gammes de forgeage. Les récentes évolutions du logiciel FORGE ont permis à Creusot Forge de développer une approche originale de simulation de ses opérations de forgeage et de traitement thermique visant à garantir la qualité de ses produits. Face au renouveau des programmes nucléaires civils et au développement de centrales de nouvelle génération, cette démarche a été largement utilisée en s'appuyant sur 40 années de savoir faire ainsi que sur une parfaite connaissance métallurgique de ses lingots

The use of hydrogenated nickel as a model system for studying solute-dislocation interactions

The effect of hydrogen on tensile tests of nickel and binary nickel – 16 wt. % chromium alloy is analysed in terms of solute drag phenomenon. Static Strain Ageing experiments are used to measure the saturated dislocation pinning force as a function of the H concentration. First order hydrogen-dislocation interactions cause a shielding of the pair interactions between edge dislocations. The influence of this screening effect is analytically evaluated on the self-energy and line tension of curved dislocations, the critical force for the expansion of a dislocation loop and the dissociation mechanism. These results are used to interpret experimental results on the plastic flow of hydrogen-charged nickel single crystals oriented for easy glide.This study illustrates the mechanisms of H-dislocation interactions and their consequences on the different contributions of hydrogen to the flow stress of nickel

Influence of Al on the High Temperature corrosion behaviour of Inconel 617 in VHTR primary coolant atmosphere

Publié suite au congrès High Temperature Corrosion and Protection of Materials 7International audienceDue to the specific in service VHTR conditions, the corrosion behaviour of Inconel 617, candidate alloy for the IHX design, has been investigated at elevated temperatures in representative helium containing impurities (CO, H2O, H-2 and CH4) in the range of mu bar. The role of Al in the corrosion behaviour of IN617 is investigated using Ni-22Cr-9Mo base model alloys containing different Al levels (from 0 to 2wt.%)

Comparison of the high temperature surface reactivity in impure helium of two materials for gas cooled reactors

International audienceNickel base alloys Haynes 230 and Inconel 617 are of interest for gas cooled reactors. At high temperature in impure helium, they generally form surface chromium-rich oxides. However above a critical temperature called T-A, the scales are not stable anymore and the chromia destruction comes with a production of carbon monoxide. Reactivity tests on model alloys, with and without carbon, prove that chromia is reduced by the carbon from the alloy. TA VS P(CO) curves were also plotted for the two commercial alloys based on the experimental determination of T-A in various atmospheres with increasing partial pressures of carbon monoxide. Unexpectedly, both materials exhibit an almost ideatical behavior although a basic equilibrium approach suggests that the chromia scale would be reduced in different conditions due to the thermodynamic particularity of the interfacial alloy/scale system

High temperature reactivity of two chromium-containing alloys in impure helium

International audienceChromium-rich nickel base alloys 617 and 230 are promising candidate materials for very high temperature gas-cooled reactors (VHTR) but they must resist corrosion in the impure primary cooling helium over very long times. The impurities of the hot helium can promote the development of chromium-rich surface oxides that appear to protect the alloys against intensive corrosion processes. However above a critical temperature (typically in the range 1173-1273 K), chromium oxide is reduced by carbon from the alloy and the surface layer is not stable anymore. Depending oil the gas composition, the unprotected material rapidly either gains or loses carbon with a dramatic impact on its mechanical properties. The deleterious reaction of chromia and carbon thus fixes all ultimate reactor operating temperature. Critical temperature measurements are presented for alloys 617 and 230 and the influence of carbon monoxide partial pressure in helium is discussed

3D dimensional measurement of large hot metallic shells

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3D characterization of hot metallic shells during industrial forging

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