HAL : hal-00507516, version 1

DOI : 10.1016/j.jnucmat.2010.05.010

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Journal of Nuclear Materials 402, 2-3 (2010) 147-156

A detailed TEM and SEM study of Ni-base alloys oxide scales formed in primary conditions of pressurized water reactor

Mohamed Sennour (  Auteur correspondant ) 1, Loic Marchetti 2, Frantz Martin 2, Stéphane Perrin 2, Régine Molins 1, Michèle Pijolat 3, 4, 5

MINES, ParisTech ; CEA Collaboration(s)

(2010)

he oxide film formed on nickel-based alloys in pressurized water reactors (PWR) primary coolant conditions (325 °C, aqueous media) is very thin, in the range of 1–100 nm thick, depending on the surface state and on the corrosion test duration. The nature and the structure of this scale have been investigated by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). TEM observations revealed an oxide layer divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni(1−x)FexCr2O4). Moreover, nodules of Cr2O3, with a size about 5 nm, were present at the interface between this spinel and the alloy. No chromium depletion was observed in the alloy, at the alloy/oxide interface. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni(1−z)Fe(2+z)O4) resulting from precipitation phenomena. SEM and TEM observations showed a link between the nucleation and/or the growth of crystallites of nickel ferrite and the crystallographic orientation of the substrate. A link between the presence of surface defects and the nucleation of the crystallites was also underlined by SEM observations. Partially hydrated nickel hydroxide, was also observed by TEM in the external scale. Based on these results, some considerations about the mechanism of formation of this oxide layer are discussed.

1 :	Centre des Matériaux (MAT)
	CNRS : UMR7633 – MINES ParisTech - École nationale supérieure des mines de Paris
2 :	Laboratoire d'Etude de la Corrosion Aqueuse (LECA)
	CEA : DEN/DPC/SCCME/LECA
3 :	Laboratoire des Procédés en Milieux Granulaires (LPMG-EMSE)
	CNRS : UMR5148 – École Nationale Supérieure des Mines - Saint-Étienne
4 :	Centre Sciences des Processus Industriels et Naturels (SPIN-ENSMSE)
	École Nationale Supérieure des Mines - Saint-Étienne
5 :	Département Procédés et évolution des systèmes avec solides (ProcESS-ENSMSE)
	École Nationale Supérieure des Mines - Saint-Étienne – SPIN

Domaine

:

Sciences de l'ingénieur/Génie des procédés

Mots Clés : TEM – SEM – nickel-based alloys – pressurized water reactors – PWR – oxide film – corrosion – high temperature – high pressure water – steam generators – SG

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Contributeur : Andrée-Aimée Toucas <>

Soumis le : Mercredi 4 Août 2010, 10:56:23

Dernière modification le : Mercredi 4 Août 2010, 12:43:19