NOMATEN ONLINE-SEMINAR October 14: Radiation-induced G-phase precipitation in FeMnNiSi ferritic alloys: Insights from ion irradiation at JANNuS (France) and neutron irradiation feasibility tests at the MARIA reactor (Poland)
NOMATEN Online Seminar
Location: gotomeeting room - https://meet.goto.com/NCBJmeetings/nomaten-seminar
Seminar date: October 14th, 2025, 1 PM (CEST)
Radiation-induced G-phase precipitation in FeMnNiSi ferritic alloys: Insights from ion irradiation at JANNuS (France) and neutron irradiation feasibility tests at the MARIA reactor (Poland)
Speaker name: Dr Estelle Meslin
Speaker affiliation: CEA Saclay, ISAS/DRMP/S2CM/SRMP, France
Abstract:
This presentation will be divided into 2 parts.
• The first part addresses a long-debated issue in the scientific community regarding the precipitation of Ni-Mn-Si-rich embrittling phases in reactor pressure vessel (RPV) steels and its potential connection to late blooming phases in irradiated reactor pressure vessel steels.
In low-copper reactor pressure vessel (RPV) steels, representative of the 16MND5, the composition and irradiation conditions under which these embrittling phases precipitate remain unknown. In this work, we investigate a copper-free Fe-MnNiSi model alloy. It was irradiated using 27 MeV Fe ions within the multi-ion beam Jannus Saclay facility in the French Atomic Energy Commission (CEA) in Saclay. at a temperature of 400°C up to damage levels ranging from 1 to 8 dpa, with a damage rate set at 10-5 dpa/s. A subsequent annealing at 400°C have been performed after irradiation up to 34 weeks. The irradiated (I) and irradiated and annealed (IA) microstructures were analyzed by integrating high-resolution transmission electron microscopy (HRTEM), high-resolution synchrotron X-ray diffraction (HR synchrotron XRD), and atom probe tomography (APT). We then obtained robust statistical data that enabled analysis of the crystallographic structure, morphology, and chemical composition of the embrittling phases, leading to their identification as G-phase. Comprehensive analysis of radiation‐induced and post‐annealed precipitate morphologies reveals several solute redistribution mechanisms, including a lattice-point-defect induced precipitation of a dense, metastable Mn-free phase, which in turn triggers the homogeneous precipitation of the less dense G-phase. We highlight point defects not only alter precipitation pathways but also significantly increases the G-phase precipitation driving force.
• In the second part, an original specimen holder designed to irradiate FIB lamellae with neutrons inside the MARIA test reactor in Poland is presented. It was used to irradiate the same Fe-MnNiSi RPV model alloys over two reactor cycles. Subsequent TEM characterization of the thin foils was successfully performed. The samples were effectively retrieved and analyzed by TEM, demonstrating the feasibility of using the MARIA reactor to irradiate small-sized FIB lamellae with neutrons.
Bio:
Dr Meslin has been working for over 20 years on the behavior of metallic materials under extreme conditions, particularly under irradiation by charged particles (such as electrons using CEA's high-voltage TEM and ions via the JANNuS facility in Saclay) or by neutrons. Her research combines advanced experimental techniques with modelling approaches to predict the evolution of the mechanical and microstructural properties of structural materials used in nuclear reactors.
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