SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2002; 34: 197–200 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1282 XPS study of oxides formed on nickel-base alloys in high-temperature and high-pressure water A. Machet, 1,2 A. Galtayries, 2∗ P. Marcus, 2 P. Combrade, 3 P. Jolivet 1 and P. Scott 1 1 Framatome ANP, Tour Framatome, 92084 Paris La D ´ efense, France 2 Laboratoire de Physico-Chimie des Surfaces, CNRS-UMR 7045, Ecole Nationale Sup ´ erieure de Chimie de Paris, 75231 Paris Cedex 05, France 3 Framatome ANP, Centre Technique, 71205 Le Creusot, France Received 16 July 2001; Revised 5 December 2001; Accepted 3 January 2002 The aim of this work is to characterize the oxidation behaviour of different nickel-base alloys exposed to high-temperature and high-pressure water for short oxidation times. The behaviour of Alloy 600 (74% Ni, 16% Cr, 9% Fe), Alloy 690 (60% Ni, 30% Cr, 9% Fe) and Alloy 800 (47% Fe, 32% Ni, 21% Cr) exposed to simulated, pressurised water reactor primary water at 325 ◦ C has been compared. From the combination of chemical and structural data obtained by XPS, nuclear reaction analysis and scanning electron microscopy, the chemical composition and the morphology of the oxide formed on the surfaces have been determined. All alloys present a duplex oxide layer composed of Fe-rich crystals in the external layer and an inner Cr-rich layer that is compact and continuous. The oxide thicknesses were 4–20 nm for Alloy 600 exposed for 0 – 400 h, 4 – 40 nm for Alloy 690 exposed for 0 – 400 h and 4 – 150 nm for Alloy 800 exposed for 0 to 150 h. The kinetics of oxidation of these samples most probably fit a logarithmic growth equation. Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: high-temperature oxidation; PWR; Alloy 600; Alloy 690; Alloy 800; XPS; nuclear reaction analysis INTRODUCTION Many previous papers 1–7 have focused on the properties of oxide layers grown on stainless steels and nickel superalloys in water at high pressure and temperature, both in dynamic flowing conditions or in static autoclaves. All describe the oxide layer as having a duplex structure formed by an inner Cr-rich layer and an outer layer consisting of well-defined octahedral Fe-rich crystals. Depending on the different experimental parameters (sample preparation, temperature, pressure, chemical composition of aqueous solution), the oxidation kinetics vary from logarithmic to exponential. Significantly fewer papers deal with the initial stages of oxidation of metallic surfaces of nickel-base alloys exposed to high-temperature, high-pressure water. The first steps of the oxidation process are likely to play an important role in longer term oxidation behaviour. One illustration is the stress crack corrosion of these alloys. As soon as a crack appears, the fresh surface is immediately in contact with high-temperature and high-pressure water. In this situation, it is the crucial phase of the oxidation process to which we have chosen to pay careful attention and to characterize the surface chemistry. Thus, after relatively short periods of oxidation, the samples were characterized mainly by x- ray photoelectron spectroscopy (XPS), but also by nuclear L Correspondence to: A. Galtayries, Laboratoire de Physico-Chimie des Surfaces, CNRS-UMR 7045, Ecole Nationale Sup´ erieure de Chimie de Paris, 75231 Paris Cedex 05, France. E-mail: galtayri@ext.jussieu.fr reaction analysis (NRA) and scanning electron microscopy (SEM). EXPERIMENTAL Tubes of commercial Alloy 600 (74 at.% Ni, 16 at.% Cr, 10 at.% Fe), Alloy 690 (60 at.% Ni, 30 at.% Cr, 10 at.% Fe) and Alloy 800 (47 at.% Fe, 32 at.% Ni, 21 at.% Cr) were cut and flattened into disks 15 mm diameter and 1 mm thick. The coupons were mechanically polished to a 0.25 μm diamond finish. During and after these preparation steps, the coupons were ultrasonically cleaned in acetone, ethanol and pure water. The coupons were oxidized in a static autoclave con- taining simulated pressurised water reactor (PWR) primary water at 325 ° C and 155 bar pressure. To conform with the PWR primary water specification, the aqueous solution was lithiated (2 ppm Li) and borated (1200 ppm B) and a hydro- gen overpressure was maintained to ensure a dissolved H 2 concentration of 35 cc kg 1 and a low oxygen content of <30 μg kg 1 . The test durations were 0 (blank test consisting of heating up to 325 ° C in PWR conditions and cooling), 20, 50, 100, 150, 200 and 400 h. Photoelectron spectroscopy studies were performed with a VG Escalab Mk II instrument using non-monochromatic Mg K˛ and Al K˛ radiation (h D 1253.6 and 1486.6 eV, respectively) at a pass energy of 20 eV. The use of two photon energies is important because of the secondary structures that appear in the spectra due to Auger transitions of the analysed elements. For example, with the Al K˛ Copyright  2002 John Wiley & Sons, Ltd.