Papers by Author: Hélène Réglé

Abstract: Nucleation and normal or abnormal grain growth of new grains have been observed in several metals and alloys during annealing after various levels of strain (from few percents for abnormal grain growth in steel and aluminium to 90 % strain for static recrystallization of highly deformed copper, zirconium and steel). For each of these cases, the links between the initial deformation state of the polycristalline samples and their final textures after annealing are analyzed in some details, by taking into acount the distribution of orientations and misorientations within the samples, as well as the repartition of stored energy . With the help of polycristalline models for the simulation of deformation and recrystallization processes, some general conclusions regarding the nucleation and growth processes are finally drawn.

Abstract: The aim of this study is to acquire more quantitative data on the cold-deformed state, in order to determine the key parameters for nucleation (like orientation gradient, dislocation density, degree of fragmentation…) and to correlate these to parameters which can be predicted by a mean field deformation model. Experimentally, a Ti-IF hot band has been deformed by cold rolling up to 51%. The deformed microstructures are finely characterised using EBSD inside the SEM. It appears then that the heterogeneity of deformation inside the grains begins very early. Some grains undergo fragmentation whereas some others deform very homogeneously. Misorientation and degree of fragmentation are found to be orientation and rolling level dependent. These deformation parameters are plotted against the Taylor factor, calculated in each grain.

Abstract: In this paper we present results obtained in collaboration between NSC and Arcelor on the austenite of a multiphased steel and on a 70%Ni-30Fe alloy. The work concerns the formation of the crystallographic textures during the recrystallisation of austenite, since these textures have a strong influence, after the phase transformation, on the forming properties of the sheets. The microstructure and the textures of the austenite and the FeNi alloy were measured with X-Ray diffraction techniques and with EBSD on a high resolution FEG-SEM.