Matériaux conducteurs à haute limite d'élasticité dans le système Cu-Mg (élaboration, caractérisation et modélisation)

Les alliages conducteurs à haute tenue mécanique sont utilisés dans de nombreux domaines tels que le transport, l énergie et l industrie électronique. La demande en ces matériaux est croissante. Les alliages Cu-Be constituent à l heure actuelle les matériaux conducteurs les plus résistants mais posent un problème de toxicité et de coût. Pour proposer une alternative à ces derniers, nous avons étudié des alliages Cu-Mg hypo-eutectiques. Deux voies de synthèse ont été utilisées afin d obtenir des composites endogènes possédant une combinaison originale de propriétés structurelles et fonctionnelles : le refroidissement conventionnel et la solidification rapide par melt-spinning. Les microstructures obtenues ont en commun la présence d agrégats eutectiques et diffèrent principalement par la dimension des paramètres métallurgiques tels que la taille de grains et la distance interlamellaire. Les systèmes présentent des forces motrices de transformation de phases importantes conduisant à une précipitation au cours d un maintien thermique. L investigation des propriétés mécaniques et électriques des alliages Cu-Mg montre que ces dernières égalent celles des alliages Cu-Be. En complément de l approche expérimentale, nous avons adapté deux modèles : un modèle thermocinétique pour décrire l évolution temporelle de la microstructure qui a lieu à haute température et un modèle mécanique permettant de rationaliser l'influence des paramètres microstructuraux sur les propriétés mécaniques et électriques.Copper-based high strength conductive alloys are used in a myriad of applications such as transport, energy and electronic industries. The demand for these materials is booming. The strongest conductive alloy is based on the Cu-Be system which has the disadvantage of toxicity and cost. In an attempt to find an alternative to these, we have developed hypoeutectic Cu-Mg alloys. Two synthesis routes were applied to produce endogenous compounds with a unique combination of structural and functional properties: the conventional cooling and the rapid solidification by melt-spinning. The obtained microstructures share the presence of eutectic aggregates and differ mainly by the size of the metallurgical parameters such as grain size and interlamellar distance. The two systems provide high driving forces for phase transformations leading to precipitation during aging. The investigation of the mechanical and electrical properties of Cu-Mg alloys shows that they are equal to those of the Cu-Be alloys. In addition to experimental approach, we have adapted two models: a thermo-kinetic one to describe time evolution of the microstructure which takes place at high temperature and a mechanical one to rationalize the influence of microstructural parameters on mechanical and electrical properties.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

A map of single-phase high-entropy alloys

High-entropy alloys have shown much interest and unusual materials properties. The stability of equimolar single-phase solid solution of five or more elements is likely to be rare and identifying the existence of such alloys has been very challenging because of the very large space of possible combinations. Herein, based on high-throughput density-functional theory calculations, we construct a chemical map of single-phase equimolar high entropy alloys by investigating over 650000 equimolar quinary alloys through a binary regular solid-solution model. We identify more than 30000 potential single-phase equimolar alloys (5% of the possible combinations) forming mainly in body-centered cubic structures. We unveil the chemistries that are likely to form high-entropy alloys, and identify the complex interplay among mixing enthalpy, intermetallics formation, and melting point that drives the formation of these solid solutions. We demonstrate the power of our method by predicting the existence of two new high entropy alloys, i.e. the body-centered cubic AlCoMnNiV and the face-centered cubic CoFeMnNiZn, which are successfully synthesized.Comment: 12 pages, 6 figures, 1 table (excluding SI

From high-entropy alloys to complex concentrated alloys

High-entropy alloys (HEAs) and related concept of complex concentrated alloys (CCAs) expand the diversity of the materials world and inspire new ideas and approaches for the design of materials with an attractive combination of properties. Here, we present a critical review of the field with the intent of summarizing the principles underlying their birth and growth. We highlight the major accomplishments and progresses over the last 14 years, especially in the discovery of new microstructures and mechanical properties. Finally, we outline the main challenges and provide guidance for future works

Studies of the effect of melt spinning on the electrochemical properties of the AB2 Laves phase alloys

A comparative study of the effect of melt spinning on the electrochemical properties of the C14 and C15 AB2 alloys has been performed. The wheel speeds of 630, 2100, and 4100 cm/s were applied during the rapid solidification of both alloys. The structural analysis of the formed phases was performed by X-ray powder diffraction (XRD), while their microstructural morphology was studied by scanning electron microscopy (SEM). In both alloys a tremendous grain refinement due to the melt spinning process was observed: In addition, melt spinning also significantly contributed to the morphological variation of the microstructural changes in C14 alloys which showed changes from the equiaxed grain at lower speed to the small dendrites at higher speed. In contrast to the C14 alloys, the morphological variation was not observed for the C15 alloys. Furthermore, for both C14 and C15 alloys melt-spun at 2100 cm/s the maximum capacities of 435 and 414 mAh/g were achieved, respectively. As both alloys revealed the significant grain refinement due to the melt spinning, an increase in electrochemical capacity was achieved. However, the melt spinning parameters need to be further optimized to improve poor activation behavior of the rapidly solidified alloys

Cu_(2)ZnGeSe_(4) Nanocrystals: Synthesis and Thermoelectric Properties

A synthetic route for producing Cu_(2)ZnGeSe_(4) nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu_(2)ZnGeSe_(4) is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450 °C