Papers by Author: Laure Martinelli

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Authors: Patrick Ganster, A. Borbely, V. Barnier, Pierre Desgardin, M.F. Barthe, Frédéric Soisson, Maylise Nastar, Laure Martinelli, Clara Desgranges
Abstract: On Ni and Ni-16wt%.Cr model-alloys compressed at 30 % and 60 % deformation, point-defects and dislocations concentrations are respectively characterized by positron annihilation spectroscopy and x-ray diffraction analysis. The positron results show that only mono-vacancies are formed during compressive test The X-ray results allows us to quantify the dislocation concentration in the systems. Saturation of defect densities is observed in measurements for these high deformation rates. In support to the experimental work, an homogeneous kinetic model is used to characterize point-defect – dislocation interactions to estimate the kinetics of vacancy restoration to equilibrium concentration.
Authors: Fanny Balbaud-Célérier, Laure Martinelli, A. Terlain, A. Ngomsik, S. Sanchez, Gerard Picard
Authors: Laure Martinelli, Fanny Balbaud-Célérier, Gerard Picard, Gerard Santarini
Abstract: The oxidation mechanism of the T91 martensitic steel in oxygen-saturated Pb-Bi eutectic at 470°C has been investigated to develop a long term predictive model of the steel oxidation kinetic. This work is performed in the frame of life duration studies carried out for the MEGAPIE spallation module demonstrator dedicated to the feasibility demonstration of an hybrid reactor. Our scientific approach has been based on an experimental characterization of the oxide scales and of the T91 steel oxidation kinetics. From these experimental results, an oxidation mechanism has been elaborated and then simulated. The oxide scale formed at the T91 surface has a duplex structure, constituted of an external magnetite scale and an internal Fe-Cr spinel scale. A scale growth mechanism has been proposed: the magnetite scale growth seems to be limited by the iron lattice diffusion inside the duplex oxide scale. At the same time, a self-regulation mechanism seems to govern the Fe-Cr spinel scale growth. This mechanism consists of a non-limiting oxygen diffusion step, which is carried out, across the oxide scale, inside liquid lead nano-channels and a limiting iron oxide lattice diffusion step. Considering the proposed oxidation mechanism, a simulation of the growth of the two oxides scales has been carried out and compared to the experimental oxidation kinetics. The excellent agreement between the experimental results and the simulations supports to accept the proposed mechanism, leading to prediction of kinetics for long oxidation durations.
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