Comportement en fluage à haute température dans le domaine biphasé (α + β) de l'alliage M5®

Abstract : The isothermal steady-state creep behavior of a M5® thin sheet alloy in a vacuum environment was investigated in the (α+β) temperature, low-stress (1-10MPa) range. To this aim, the simplest approach consists in identifying α and β creep flow rules in their respective single-phase temperature ranges and extrapolating them in the two-phase domain. However, the (α+β) experimental behavior may fall outside any bounds calculated using such creep flow data. Here, the model was improved for each phase by considering two microstructural effects: (i) Grain size: Thermo-mechanical treatments applied on the material yielded various controlled grain-size distributions. Creep tests in near-α and near-β ranges evidenced a strong grain-size effect, especially in the diffusional creep regime. (ii) Chemical contrast between the two phases in the (α+β) range: From thermodynamic calculations and microstructural investigations, the β phase is enriched in Nb and depleted in O (the reverse being true for the α phase). Thus, creep tests were performed on model Zr-Nb-O thin sheets with Nb and O concentrations representative of each phase in the considered temperature range. New α and β creep flow equations were developed from this extended experimental database and used to compute, via a finite element model, the creep rates of the two-phase material. The 3D-morphology of phases (β grains nucleated at α grain boundaries) was explicitly introduced in the computations. The effect of phase morphology on the macroscopic creep flow was shown using this specific morphology, compared to other typical morphologies and to experimental data. M5® is a registered trademark of AREVA NP.
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Submitted on : Tuesday, April 17, 2012 - 9:26:14 AM
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  • HAL Id : pastel-00688207, version 1

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Gwenaël Trégo. Comportement en fluage à haute température dans le domaine biphasé (α + β) de l'alliage M5®. Matériaux. École Nationale Supérieure des Mines de Paris, 2011. Français. ⟨NNT : 2011ENMP0084⟩. ⟨pastel-00688207⟩

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