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Méthodologie instrumentale à l'échelle atomique pour une meilleure compréhension des mécanismes de ségrégation intergranulaire dans les aciers : application au phosphore.

Abstract : It is well known that the intergranular segregation of phosphorus can diminish the cohesion between grains, resulting in steel embrittlement. Low alloyed bainitic steels used to build nuclear reactor pressure vessel (RPV) generally contain a small amount of phosphorus (in the range of 100 ppm). Continuous exposure to a low neutron dose rate irradiation at intermediate temperature (~300°C) results in radiation embrittlement of RPV steel. Since intergranular segregation of phosphorous can contribute to this embrittlement, for purpose of RPV reliability during operation, it is important to understand the effects of ageing conditions (temperature, irradiation dose etc.), material composition and grain boundary (GB) type on the intensity of phosphorus intergranular segregation. Regarding to literature sources, it was revealed that the intergranular segregation values may strongly vary among different GBs. However, there is a lack of systematic studies in this field.In order to get an accurate and representative description of GB from structural and chemical points of view, different techniques are combined in this work. Atom Probe Tomography technique is utilized as the main tool. This technique is able to explore the 3D atomic distribution of broad variety elements at GB. GB geometry is determined from Transmission Kikuchi Diffraction (TKD) map supplemented by APT reconstruction. To gain a better understanding of segregation mechanisms, models of thermally and radiation-induced segregation were employed.
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Submitted on : Monday, April 16, 2018 - 11:42:10 AM
Last modification on : Thursday, November 28, 2019 - 3:08:41 AM

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Alfiia Akhatova. Méthodologie instrumentale à l'échelle atomique pour une meilleure compréhension des mécanismes de ségrégation intergranulaire dans les aciers : application au phosphore.. Science des matériaux [cond-mat.mtrl-sci]. Normandie Université, 2017. Français. ⟨NNT : 2017NORMR131⟩. ⟨tel-01767494⟩

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