Papers by Author: Marie Helene Mathon

Abstract: Small Angle Neutron Scattering (SANS) technique allows to characterize at a nanoscale the microstructure of the ferritic martensitic steels and ODS FeCr alloys which are candidates for the internal structures of future nuclear reactors. Firstly, the microstructure evolution induced by neutron irradiation at high dose in conventional and Reduced Activation Fe9%Cr martensitic steels is presented. Then, a SANS study of Oxide Dispersion Strengthened (ODS) alloys is also presented. The main objective is to control the nano-size oxide particles at the various stages of the fabrication process.

Abstract: The objective of this study is to investigate the effects of Heat Affected Zone produced by Plasma Transferred Arc process and residual stress in substrate steel 55NiCrMoV7. In this study, based on ABAQUS code, a sequentially coupled thermal, metallurgical, mechanical 2-D finite element model is developed. In the numerical simulations, the coating and Heat Affected Zone are used to predict the residual stresses. The simulation results revealed that the final residual stress in substrate steel do seem to be influenced by the HAZ.

Abstract: The Stellite 6 hardfacing alloys have been deposited on steel substrate using a Plasma Transferred Arc (PTA) with complex geometry. The residual strain of the PTA technology at the surface of coating layer and the interface were determined by neutron diffraction method. In the present work, a numerical model for the residual stresses formed during the PTA process with physical conditions and mechanical properties using the Abaqus code is analysed. The result reveals that the residual stresses obtained by the numerical simulation are in very good agreement with experimental results by the neutron diffraction.

Abstract: By associating texture determinations and strains measurements by neutron diffraction, the elastoplastic behaviours of families of crystallites with the same crystallographic orientations were characterized in situ in a brass and a bronze alloys under uniaxial loading. The polycrystalline orientation analysis method proposed here allows an intermediate approach between a “local” (intragranular) and a “global” characterization, within the bulk of massive samples.

Abstract: The present work is an attempt to understand the recrystallisation mechanisms in Fe-3% Si alloys used in transformer cores. After secondary recrystallisation silicon steels exhibit a Goss texture with a more or less important spread depending on the details of the processing route, namely, Conventional Grain Orientation CGO or High Permeability Hi-B. The mechanisms of Goss grain formation during hot rolling and primary recrystallisation, as well as those controlling the first steps of abnormal growth, are not yet well understood. The present work mainly deals with texture characterization of the hot rolled state. Surface, quarter and half thickness samples are prepared from hot-rolled sheet. Global and local textures are characterized by neutron diffraction and electron backscattered diffraction, respectively. The Orientation Distribution Functions and the volume fraction of the different texture components are calculated. The components from global texture measurements are (001)[1-10], (112)[1-10] (α fiber ), (011)[100] (Goss) and (111)[1-21] (111) [1-10](γ fiber). EBSD measurements have shown large variations of texture from the surface to the half thickness of the sheet. These local measurements are related to the global results by rotation about the transverse direction. Moreover, the grain size appears to be inhomogeneous.

Abstract: The crystallographic texture of electrolytic tough pitch copper has been investigated by neutron diffraction after deformation by cold wire-drawing (reduction of area between 51 and 94 %) and after static recrystallization. The deformation texture characterized by a strong <111> fiber is reinforced with increasing strain, while the volume fraction of <100> fiber is reduced. In turn, we show that the <100> fiber is strongly reinforced after recrystallization when intensity of the <100> maxima increases with the level of deformation. Since the <111> fiber disappears first during annealing, the static recrystallization has been followed “in situ” by measurements of the diffracted intensity evolution in the center of the {111} pole figure. From these experimental data and taking into account the Arrhenius equation, the activation energy of the recrystallization process has been determined for each deformation rate.

Abstract: Materials of ultra-fine grained microstructure (sub-micrometer grain size) exhibit large strength, hardness and ductility and also the increased toughness in comparison with conventional coarse-grained ones. In these materials also the super-plastic flow at lower temperatures is observed. This behaviour may be interesting when aluminium alloys like AlCuZr, used in superplastic forming, are considered. In the paper, the methods of preparing such materials by equal-channel angular pressing (ECAP) is proposed and the texture analysis, based on neutron diffraction pole figure measurements and calculated orientation distribution function of two alloys AlCu4SiMn and AlCu5AgMgZr is discussed. The influence of short time recrystallization is discussed in relation with TEM and SEM observations.

Abstract: In order to simulate the recrystallization process, Monte Carlo modelling has been applied to the case of wire-drawn copper deformed to a moderate strain. The complete experimental set of data was taken mainly from Electron Back Scattered Diffraction measurements in a Scanning Electron Microscope. Several nucleation hypothesis have been introduced and tested into the model. It has been shown that nucleation taking into account the sites associated with the highest stored energy and highest local misorientation leads to the best results in terms of recrystallization microstructure and texture. An important number of new orientations - that come only from annealing twinning - are not reproduced with the model, indicating the major role of this particular mechanism during the recrystallization process.

Abstract: Cold-drawn Electrolytic Tough Pitch copper wires have been investigated with Neutron Diffraction and Electron Back Scattered Diffraction. The drawn copper wires (38% reduction in area) develop major <111> and minor <001> fiber textures. It appears that the texture intensity of the reinforcements within the <111> and <001> fibers is more pronounced in the center and intermediate part of the wires. During the first annealing time, it is found that the recrystallization kinetics is enhanced when oxygen content is increased. The recrystallized fraction within the intermediate zone of the wire is two times larger in the cathode with higher oxygen content. The mechanisms at the origin of this acceleration of recrystallization kinetics will be discussed taking into account the presence of Cu2O type oxides.

Abstract: Wire-drawn Electrolytic Tough Pitch copper deformed at moderate strain has been investigated with Electron Back Scattered Diffraction in a Scanning Electronic Microscope in order to evaluate the recrystallization mechanisms at the meso-scale. Experimentally, it has been shown that the static recrystallization takes place first in the highly deformed and misoriented areas, in the intermediate regions of the wire. The grains related to the <100> fiber nucleate and grow first in these regions, but some other orientations (including the <111> oriented grains) - that have a combined nucleation/growth potential - develop in second time. The annealing twinning is active from the beginning of the recrystallization and tends to randomize the final recrystallization texture.