Titanium and zirconium oxidation under argon irradiation in the low MeV range
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Titanium and zirconium oxidation under argon irradiation in the low MeV range Dominique Gorse-Pomonti1, Ngoc-Long Do1, Nicolas Bérerd2, Nathalie Moncoffre2 and Gianguido Baldinozzi3 1 Laboratorie des Solides Irradiés, UMR CNRS 7642, Ecole Polytechnique, F-91128, Palaiseau Cedex, France. 2 Institut de Physique Nucléaire de Lyon, UMR CNRS 5822, F-69622, Villeurbanne Cedex, France. 3 Matériaux Fonctionnels pour l’Energie, SPMS CNRS-Ecole Centrale Paris, Châtenay-Malabry, France ABSTRACT We studied the irradiation effects on Ti and Zr surfaces in slightly oxidizing environment (rarefied dry air, 500°C) using multi-charged argon ions in the low MeV range (1 – 9 MeV) to the aim of determining the respective role of the electronic and nuclear stopping power in the operating oxidation process under irradiation. We have shown that ballistic collisions contribute significantly to the enhanced Ti and Zr oxidation under MeV argon bombardment. We have also shown that the projectile energy plays a significant role in the overall process. A significant oxide film thickening is visible on titanium under irradiation, taking the form of a well-defined oxidation peak between 1 and 4 MeV, as a result of the Nuclear Backscattering Spectroscopy and Spectroscopic Ellipsometry studies. A significant oxide film thickening is also visible on zirconium under same irradiation conditions, at 4 and 9 MeV, as a result of the NBS study. Work is in progress in order to determine how the modified oxidation process depends in this case on the projectile energy. INTRODUCTION In a first paper, we proved that large rather circular craters (of diameter in between 200 and 400 nm and of depth not exceeding a few tens of nm) form at the surface of titanium bombarded by an argon ion beam (3 x 1010 ions cm-2s-1) of 4 MeV or 9 MeV during 3 hours at 500°C under rarefied air pressure [1]. This result was rather unexpected and encouraged us to continue this study of the radiation damages caused to metallic surfaces by multi-charged heavy ions in the low MeV range under similar environmental conditions. To our knowledge, superficial damages in this energy range were until now very little studied. Indeed, as seen in figure 1, if we plot the nuclear (Sn) and electronic (Se) stopping power versus ion energy for the Ar/Ti system already studied, and for the Ar/Zr system studied here, we observe that the radiation damages should be produced as a result of combined nuclear and electronic energy losses between 1 and 9 MeV [2]. Moreover those damages could possibly differ largely from the cases in which only one stopping mechanism is operating. In this short paper, we will show that argon ion irradiation in the low MeV range produces damages on both titanium and zirconium surfaces under rarefied air, that take the form of accelerated oxidation, and more specifically will appear unexpectedly as an oxidation peak as function of the argon ion energy around 3 MeV on titanium but also very presumably on zirconium, under the above mentioned environmental conditions.
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