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CORROSION OF TITANIUM ALLOYS IN PRESSURISED WATER AT 300 °C AND 350 °C

Abstract : A EUROCORR In the future, some parts of the nuclear pressurised water reactor primary circuit components made of stainless steels and nickel-based alloys could potentially be made of titanium alloys. The use of titanium alloys may facilitate maintenance operations thanks to their low neutron activation. However, resistance of titanium alloys to corrosion in such conditions is poorly known. The goal of the present study is the determination of the influence of temperature on the mechanisms and the kinetics of corrosion and on the hydrogen uptake of three titanium alloys: Ti CP (α-phase), Ti 64 or Ti¬6Al¬4V, (4 vol% of β phase) and Ti10-¬2-¬3 (38 vol% of β phase). One-millimeter-thick polished flat specimens of each of these alloys were exposed to pressurized water in a stainless steel corrosion loop up to 3500 h at 300 °C and up to 1750 h at 350 °C both at pH ≈ 7.5 at a fluid velocity of 2.10­3 m.s-1. A dissolved hydrogen concentration of 2.25 mgH2/kgH2O was imposed by the hydrogen gaz pressure (0.14 MPa) in the vessel of the cold part of the loop. The oxide layers were then characterised by scanning electron microscopy (SEM), Raman spectroscopy, X-Ray diffraction, transmission electron microscopy (TEM), photoelectrochemistry and glow discharge – optical emission spectroscopy (GD-OES). The metal thickness affected by corrosion was estimated by SEM on specimens’ cross sections and by mass gain. The hydrogen uptake was measured by the melting under inert gas technique. A continuous dense oxide layer of about 30 nm thick was formed by oxidation by water at both temperatures on the three alloys considered. At 300 °C, it was made of TiO2 rutile for Ti CP (the stable phase in these conditions) and of TiO2 anatase for Ti 64 and Ti10-2-3. In parallel, oxide dissolution and precipitation phenomena led to the formation of TiO2 anatase and FeTiO3 ilmenite crystallites with a diameter ranging from 0.1 µm to 10 µm located on top of the continuous oxide layer. The thickness of the continuous oxide layer remained constant with increasing exposure duration, whereas the mass gain, the hydrogen uptake and the metal thickness affected by corrosion increased quasi-linearly with exposure duration. Corrosion kinetics were almost identical for all the studied alloys. For each alloy, mass gain and hydrogen uptake rates were approximately five times higher at 350 °C than at 300 °C. The corrosion rates were about 3 µm.year-1 at 300 °C and 15 µm.year-1 at 350 °C. Hydrogen uptake rates were five to ten times higher at 350 °C than at 300 °C and depended on the alloy. Hydrogen uptake was 50 wppm, 90 wppm and 235 wppm for Ti CP, Ti 64 and T10-2-3 respectively at 350 °C after 1750 hours. We suggest that this difference is related to the fraction of β phase as hydrogen’s solubility and diffusivity are much higher in the cubic phase than in the hexagonal one.
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Conference papers
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https://hal-cea.archives-ouvertes.fr/cea-02468696
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Submitted on : Thursday, February 6, 2020 - 9:00:21 AM
Last modification on : Wednesday, October 14, 2020 - 4:19:25 AM

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  • HAL Id : cea-02468696, version 1

Citation

Sabrina Selva, Quentin Bignon, Quentin Auzoux, Frantz Martin, Amandine Raynal, et al.. CORROSION OF TITANIUM ALLOYS IN PRESSURISED WATER AT 300 °C AND 350 °C. EUROCORR, Sep 2019, Séville, Spain. ⟨cea-02468696⟩

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