Effet de l'oxygène et de l'yttrium sur la nanoprécipitation et sur la recristallisation dans un alliage ODS Fe-14Cr

Abstract : Fe—14Cr ODS ferritic alloys reinforced by a dispersion of oxides rich in Y, Ti and O are considered suitable structural materials structural for the 4th generation of nuclear reactors. They combine neutron irradiation resistance and excellent mechanical properties, especially creep properties at high temperatures. This work is dedicated to the understanding of the effects induced by a small oxygen and yttrium variation around a reference chemical composition: Fe—14Cr—0,3Ti—0,3Y₂O₃. We showed that the crucial parameter is the precipitation kinetic of the nano-reinforcements which is responsible for the microstructure evolution before, after or during the thermal annealing. This kinetic is proper to the nature of the precipitating phases, their structure and to the orientation relationships at the particle/matrix interfaces. This last parameter determines the stability of the nano-reinforcements, hence the recrystallization mechanisms and their mechanical properties. The concentration variation of oxygen and yttrium can induce similar consolidated states in terms od nano-dispersion and mechanical properties even if the underlying mechanisms are different. Both the oxygen and yttrium enrichments lead to a recrystallization of the material at 1300°C by compltetly different mechanisms. This study allows to propose threshold values of 0,3% Fe₂O₃ and 0,7% yttrium, that should not be exceeded in order to maintain the quality of the mechanical properties.
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Marc-Antoine Thual. Effet de l'oxygène et de l'yttrium sur la nanoprécipitation et sur la recristallisation dans un alliage ODS Fe-14Cr. Science des matériaux [cond-mat.mtrl-sci]. Université Paris-Saclay, 2017. Français. ⟨NNT : 2017SACLS521⟩. ⟨tel-01725153⟩

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