High-throughput in-situ characterization and modelling of precipitation kinetics in compositionally graded alloys

The development of new engineering alloy chemistries is a time consuming and iterative process. A necessary step is characterization of the nano/microstructure to provide a link between the processing and properties of each alloy chemistry considered. One approach to accelerate the identification of optimal chemistries is to use samples containing a gradient in composition, ie. combinatorial samples, and to investigate many different chemistries at the same time. However, for engineering alloys, the final properties depend not only on chemistry but also on the path of microstructure development which necessitates characterization of microstructure evolution for each chemistry. In this contribution we demonstrate an approach that allows for the in-situ, nanoscale characterization of the precipitate structures in alloys, as a function of aging time, in combinatorial samples containing a composition gradient. The approach uses small angle x-ray scattering (SAXS) at a synchrotron beamline. The Cu-Co system is used for the proof-of-concept and the combinatorial samples prepared contain a gradient in Co from 0% to 2%. These samples are aged at temperatures between 450{\textdegree}C and 550{\textdegree}C and the precipitate structures (precipitate size, volume fraction and number density) all along the composition gradient are simultaneously monitored as a function of time. This large dataset is used to test the applicability and robustness of a conventional class model for precipitation that considers concurrent nucleation, growth and coarsening and the ability of the model to describe such a large dataset.Comment: Published in Acta Materiali

Modelling the precipitation of NbC on dislocations in a-Fe

A model has been developed for describing the precipitation of NbC on dislocations in ferrite in an Fe–C–Nb steel. This model is a continuous description of the classical laws for nucleation growth and coarsening, which are adapted to the specific case where precipitates only form on dislocations. This model is successfully applied on an extensive data set obtained by small-angle neutron scattering for a wide temperature range and two alloy contents. Using this model, it is possible to estimate the effects of process parameters on the final microstructure and, notably, it is shown that the initial dislocation density has a pronounced influence on the maximum precipitate density

Vies moyennes de quelques niveaux du noyau 19F

Les énergies d'excitations et les vies moyennes de 9 niveaux du 19 F d'énergie inférieure à 6 MeV ont été déterminées à l'aide de la réaction 18O(d, nγ) 19F. De ces vies moyennes, mesurées à partir de la méthode du déplacement Doppler, ont été déduites certaines largeurs de transition M1 qui sont comparées aux prédictions de modèles en couches

Mean magnitude variations of earthquakes as a function of depth: Different crustal stress distribution depending on tectonic setting

International audienceThe mean magnitude of earthquakes in the Gulf of Corinth is found to increase strongly with depth (b-value decreases), whereas the dip of fault planes decreases. The b-value difference of 0.25, between shallow and deep earthquake distributions, is based on about 7,000 events and therefore is statistically highly significant. The same is true in California, but opposite patterns are observed in southern Iceland and in western Nagano, Japan. Because large mean magnitudes (low b-values) are indicative of relatively high stress levels, we propose that in the detachment layer at about 9 ± 2 km depth, earthquakes are generated at higher stresses than in the shallower parts of the crust. The correlation of low b-values with low faulting dips can be taken as line of evidence that low b-values map high stress regimes

Sea surface temperature of the coastal zones of France

The results of an investigation to map the various thermal gradients in the coastal zones of France are presented. Paricular emphasis is given to the natural phenomena and man made thermal effluents. It is shown that a close correlation exist between wind speed direction and the offshore width of the effluent