Papers by Author: Michel Humbert

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Authors: Pierre Blaineau, Lionel Germain, Michel Humbert, Nathalie Gey
Abstract: We propose a new approach to automatically reconstruct the  orientation map from the ’ map inherited by the bainitic or martensitic ’ phase transformation. Our model comprises two main steps (1) identification of reliable fractions of parent grains – each  fraction orientation is determined from neighbouring variants related to a unique  orientation with a low tolerance angle; (2) expansion of these fractions by collecting adjacent variants being in orientation relation (OR) with the  orientation of the initial fraction - using now a higher tolerance around the strict OR. The code was tested on ’ maps we built from reference  maps to control some characteristics of the transformation, i.e. the type of OR used, the spread around OR, the number of inherited variants. The results show that even with a large spread around OR, the shape and orientation of most of the  grains are accurately calculated.
Authors: Nathalie Gey, Michel Humbert, Elisabeth Gautier, Jean Luc Béchade
Authors: Michel Humbert, S.R. Dey, Emmanuel Bouzy, Alain Hazotte
Abstract: The orientations of the inherited tetragonal (resp. cubic) variants are calculated from the parent hcp orientation in the case of a strict orientation relation. The numbering of the variants is proposed, as well as the misorientations between them. Conversely, a method for calculating the parent hcp orientation from a sufficient number of inherited variants is proposed. It is based on orientation correlating and orientation averaging, and it is particularly useful when the inherited variants are not exactly related to the parent orientation by a strict orientation relation or when the orientations of the inherited volumes slightly vary at different locations of the variant. The method is illustrated by considering the a to g phase transformation taking place in TiAl-based alloys
Authors: Lionel Germain, Pierre Blaineau, Nathalie Gey, Michel Humbert
Abstract: In this contribution, we describe the basic principles to reconstruct parent microtextures from inherited ones. The different methods published in the literature are examined. Their various approaches lead to different restitution capabilities and we discuss their advantages and weaknesses.
Authors: Michel Humbert, Pierre Blaineau, Lionel Germain, Nathalie Gey
Abstract: In this contribution, we investigate a method able to determine the local representative orientation relation occurring in phase transformation of steels. It is based on the analysis of sets of variant orientations and does not require the knowledge the parent austenite orientation. The method which is an optimization scheme employing quaternions allowed us to determine and investigate ORs of different low carbon steel products.
Authors: Claude Esling, Michel Humbert, M.J. Philippe, Francis Wagner
Authors: B. Petit, Nathalie Gey, Michel Humbert, Bernard Bolle, M. Cherkaoui
Abstract: A micromechanical model was used to simulate the mechanical behaviour, the transformation kinetic and the texture evolutions of a 304 stainless steel, deformed by tensile tests at T=–60°C. When the transformation strain is calculated with the phenomenological theory, the model does not very well predict the observed transformation rate and the texture evolution of the main γ grain orientations. XRD and EBSD analyses show that the martensitic transformation of γ phase into α’ martensite involves the intermediate ε phase. From these observations, new simulations were performed in which only the γ→ε transformation strain is considered in competition with classical plasticity of austenite. The α’ variants were calculated in a second step, from the ε variants selected in the micromechanical model. Among the 6 potential α’ variants able to nucleate from the same ε variant, the best oriented ones, with respect to the applied stress were selected. Under these conditions, the numerical simulations reproduce the experimental results in a more satisfying way.
Authors: Andrzej Baczmanski, Albert Tidu, Paul Lipiński, Michel Humbert, Krzysztof Wierzbanowski
Abstract: A new method for calculation of the diffraction elastic constants, based on the selfconsistent model, is proposed and tested. This method is especially useful in the interpretation of the results of X-ray measurements since the ellipsoidal inclusion near the sample surface is considered. In X-ray diffraction the information volume of the sample is defined by absorption, causing unequal contribution of different crystallites to the intensity of the measured peak. Consequently, the surface grains participate more effectively in diffraction than the grains which are deeper in the sample.
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