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

On the Deformation of Dendrites During Directional Solidification of a Nickel-Based Superalloy

Abstract: Synchrotron X-ray imaging has been used to examine in situ the deformation of dendrites that takes place during the solidification of a nickel-based superalloy. By combining absorption and diffraction contrast imaging, deformation events could be classified by their localization and permanence. In particular, a deformation mechanism arising from thermal contraction in a temperature gradient was elucidated through digital image correlation. It was concluded that this mechanism may explain the small misorientations typically observed in single crystal castings

O cloral como aplicação externa.

As propriedades desinfectantes do cloral são muitas vezes utilizadas no tratamento das feridas ou de cavidades que contenham líquidos infectos. Segue as proporções

Personnes agees et pratiques physiques en milieu associatif: analyse de la contribution du CO.DE.R.S. 86

Available from INIST (FR), Document Supply Service, under shelf-number : TD 81084 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Solidification de monograins base nickel : microstructure et qualité cristalline

Not availableNous avons cherché à caractériser et à comprendre l'origine des défauts de qualité cristalline dans des pièces monogranulaires réalisées en fonderie à cire perdue avec le superalliage base nickel AM1. Les techniques utilisées pour cela sont la métallographie, la microanalyse x, la topographie x et la diffraction gamma. Les pièces étudiées peuvent être divisées en différentes parties, qui correspondent soit à des zones d'extension du grain, soit à des zones de croissance à section constante. L’extension du grain se fait par un mécanisme de multiplication des axes dendritiques qui aboutit à la formation d'alignements d'axes primaires, qui sont également des entités cristallographiques. Par contre, dans les branches à section constante, le réseau dendritique perd progressivement de sa régularité en même temps que l'on observe une dégradation de la qualité cristalline du matériau. Les désorientations des dendrites situées en périphérie du grain initial sont à l'origine de l'apparition de secteurs d'orientations cristallines différentes. La forme de ces secteurs est donnée par les conditions macroscopiques d'échanges thermiques. La géométrie de la pièce détermine la possibilité éventuelle de développement des secteurs formes qui apparaissent alors comme des sous-grains. On propose d'expliquer la dégradation de la qualité cristalline dans les branches à section constante par l'existence de déformations ayant une origine thermomécanique. Il a été montré que la très forte variation du coefficient de dilatation linéaire associée à la précipitation conduit au développement de contraintes non négligeable