Setting-up rules to characterize microsegregation

Characterization of chemical heterogeneities such as microsegregation resulting from solidification of metallic alloys is most often performed by EDS or WDS microanalysis with spot measurements located at corners of a regular grid. Rather than attempting a theoretical treatment of the statistics of such analyses, the quality of the procedure has been investigated by implementing “measurement” grids on numerical images that mimic solidification structures. Microstructures either with no geometrical constraints (uniform distribution of the solid nuclei) or with limited constraints that give some periodicity have been investigated. Systematic analysis of the effect of the location and size of the “measurement” grid enlightens the procedures which should be followed to minimize bias

Resampling technique applied to statistics of microsegregation characterization

Characterization of chemical heterogeneities at the dendrite scale is of practical importance for understanding phase transformation either during solidification or during subsequent solid-state treatment. Spot analysis with electron probe is definitely well-suited to investigate such heterogeneities at the micron scale that is relevant for most solidified products. However, very few has been done about the statistics of experimental solute distributions gained from such analyses when they are now more and more used for validating simulation data. There are two main sources generating discrepancies between estimated and actual solute distributions in an alloy: i) data sampling with a limited number of measurements to keep analysis within a reasonable time length; and ii) uncertainty linked to the measurement process, namely the physical noise that accompanies X-ray emission. Focusing on the first of these sources, a few 2-D composition images have been generated by phase field modelling of a Mg-Al alloy. These images were then used to obtain "true" solute distributions to which to compare coarse grid analyses as generally performed with a microanalyser. Resampling, i.e. generating several distributions by grid analyses with limited number of picked-up values, was then used to get statistics of estimates of solute distribution. The discussion of the present results deals first with estimating the average solute content and then focuses on the distribution in the primary phase

Microstructure Evolution in an Aluminum Cladded Sheet during Vacuum Brazing

Microstructure evolution of a 3003 sheet cladded with 4004 brazing alloy is investigated during slow heating (1K/min) under secondary vacuum up to isothermal brazing temperature (590°C). Optical and scanning microscopies, EDS chemical analysis and EBSD orientation mapping are used. Experimental results are discussed in the light of thermodynamic calculations using Thermo-Calc. Comparisons show good agreement as long as Mg vaporization does not take place

Solidification sequence of Ni-Si-Cr ~3wt% B brazing alloys

Various Ni-Si-Cr-B brazing alloys with a similar boron content (3 wt%) are investigated. Alloy compositions cover a section of the quaternary phase diagram that connects BNi-3 to BNi-9 ternary alloys for industrial use. Samples were melted and solidified at low cooling rate (1 K/min) under secondary vacuum to minimize oxidation and the metastable phase formation. Transformation temperatures, microstructures, and chemical analyses are reported. Experimental conditions were found to play a significant role on the accuracy of obtained data. Thermodynamic data were collected upon heating. Before analyzing quaternary alloys, the results of investigated ternary alloys were compared with the literature and discussed.The authors thank Etablissements Chpolansky, Marcoussis, France, which kindly provided the certified commercial brazing alloys. Dr. J. Zollinger calculated the equilibrium ternary alloy phase diagrams with Thermo-Calc® and the TTNi7 database. M. Bertrand, master student, also contributed to this study. Finally Dr. L. Peltier and P. Charbonnier realized a secondary vacuum furnace which allowed melting of these alloys. The authors thank NSERC and CRIAQ for their indirect financial support on related projects

Variations of the Elastic Properties of the CoCrFeMnNi High Entropy Alloy Deformed by Groove Cold Rolling

The variations of the mechanical properties of the CoCrFeMnNi high entropy alloy (HEA) during groove cold rolling process were investigated with the aim of understanding their correlation relationships with the crystallographic texture. Our study revealed divergences in the variations of the microhardness and yield strength measured from samples deformed by groove cold rolling and conventional cold rolling processes. The crystallographic texture analyzed by electron back scattered diffraction (EBSD) revealed a hybrid texture between those obtained by conventional rolling and drawing processes. Though the groove cold rolling process induced a marked strengthening effect in the CoCrFeMnNi HEA, the mechanical properties were also characterized by an unusual decrease of the Young’s modulus as the applied groove cold rolled deformation increased up to about 0.5 before reaching a stabilized value. This decrease of the Young’s modulus was attributed to the increased density of mobile dislocations induced by work hardening during groove cold rolling processing

Challenges for R&D in Material Science : Example of Lorraine Region, France

International audienceThe paper deals with the recent problems that French science and industry encountered during their long-life development. This is mainly concerned with metallurgy and materials science in the Mosel river’s valley. French government in conjunction with local and international industrial giants in the field of metallurgy and materials science has already created numerous perspective research centers and laboratories aimed at effective collaboration between science and industry. The collaboration is organized in 4 R&D axes relative to industrial routes: Elaboration and Heat Treatments, Surface Treatment and Functionalizing, Shaping and Machining, Joining

Methodology to characterize microsegregation

Chemical microsegregation resulting from solidification of metallic alloys is most often characterised by EDS or WDS microanalysis using spot measurements located along a regular grid. Due to experimental limitations, the wave lengths of both dendrite arms and analysis grid are often of the same order of magnitude. Although this fact is generally eluded, it complicates the statistical analysis of the results, in particular when the objective is to validate a given solidification model or to prove the occurrence of solid state diffusion. This is first illustrated in the present work by means of experimental analysis performed on an Al alloy. The problem is then tackled using 2D simulations of more or less periodic solidification structures which are sub-sampled along periodic or random point distributions of different surface densities. Statistics tools are used to compare the resulting chemical distributions with the solidification model (Gulliver-Scheil model) injected in the simulation. This allows pointing out the limitations of classical statistical approach in that case, and finally to propose an optimum –at least less bad- procedure to characterise microsegregated structures

Caractérisation et prévision des structures en bandes dans les aciers Dual-Phase (lien avec les propriétés d'endommagement)

Les aciers Dual-Phase constituent plus de 50% du poids des automobiles récentes. Ils associent une très bonne formabilité à une haute limite à rupture. Cet excellent compromis mécanique résulte de leur microstructure biphasée, constituée d une phase martensitique dure englobée dans une matrice ferritique ductile. Ces aciers contiennent principalement du carbone et du manganèse. Les ségrégations chimiques formées lors de la coulée créent, à l issue des traitements thermo-mécaniques ultérieurs, des structures en bandes ferrito-martensitiques néfastes aux propriétés d endommagement. Les principaux objectifs de cette thèse étaient de comprendre les mécanismes de formation des bandes, et de relier leurs caractéristiques (intensité, topologie ) aux paramètres du procédé. Des cycles thermiques inspirés du procédé industriel ont été réalisés sur des échantillons d une nuance représentative (Fe-0.15%C-1.5%Mn). Plusieurs techniques expérimentales (dilatométrie, microscopies, sonde électronique, EBSD ) ont été mises en oeuvre pour comprendre les mécanismes de développement des microstructures. Des outils de visualisation et de quantification de la topologie bidimensionnelle et tridimensionnelle des microstructures ont été développés, permettant d'évaluer l influence des paramètres du traitement thermique sur la microstructure finale. Pour différentes topologies, les champs de contraintes locaux responsables de l endommagement ont été estimés à l aide de simulations par éléments finis. Les informations recueillies permettront d alimenter des modélisations numériques visant à reproduire la genèse des microstructures et à prévoir leur comportement mécanique en grande déformationModern cars are composed in weight of more than 50% of Dual-Phase steels. They combine a very good formability and high level of strength. This excellent mechanical accommodation is due to their two-phase microstructure, composed of hard martensite phase in a ductile ferrite matrix. These steels contain principally carbon and manganese. Chemical segregations developed during the casting create, after subsequent thermo-mechanical treatment, banded structures of ferrite and martensite unfavorable for damaging properties. Main objectives of this thesis were to understand mechanism of bands formation, and link their characteristic (intensity, topology ) to the process parameters. Some heat treatment routes derived of the industrial process were realized on sample of representative grade (Fe-0.15%C-1.5%Mn). Several experimental techniques (dilatometry, microscopy, electronic probe, EBSD ) were operating to understand mechanism of microstructures development. Some tool of visualization and quantification of the two-dimensional and three-dimensional were developed, enable to evaluate the influence of heat treatment parameters on the final microstructure. For different topologies, the local stress fields liable of damaging were estimated with the support of finite elements simulations. The collected information will allow loading numerical modeling with the purpose to reproduce microstructures genesis and to predict their mechanical behavior in high strainMETZ-SCD (574632105) / SudocSudocFranceF