Mechanical alloying of Cu and Fe induced by severe plastic deformation of a Cu-Fe composite

A filamentary composite elaborated by cold drawing was processed by High Pressure Torsion (HPT). The nanostructure resulting from this severe plastic deformation (SPD) was investigated thanks to scanning electron microscopy, transmission electron microscopy, X-ray diffraction and 3D atom probe. Although the mutual solubility of Cu and Fe is extremely low at room temperature in equilibrium conditions, it is shown that nanoscaled Fe clusters dissolve in the Cu matrix. The non-equilibrium copper supersaturated solid solutions contain up to 20at.% Fe. The driving force of the dissolution is attributed to capillary pressures and mechanisms which could enhanced the atomic mobility during HPT are discussed. We conclude that the interdiffusion is the result of a dramatic increase of the vacancy concentration during SPD.Comment: 20 page

Atomic scale characterization of the nucleation and growth of SnO2 particles in oxidized CuSn alloys

The internal oxidation of Sn was investigated to understand the oxidation kinetics of monophase CuSn alloys. SnO2 particles were characterized by analytical transmission electron microscopy. The orientation relationship between SnO2 and Cu was determined with a special emphasis on the atomic scale structure of Cu/SnO2 interfaces (misfit dislocations and chemical structure). Habit planes with a pure oxygen plane terminating the SnO2 phase are greatly favored and large misfits promote the growth of plate shaped precipitates

Nanostructure of a cold drawn tempered martensitic steel

The carbon atom distribution in a tempered martensitic steel processed by cold drawing was investigated with a three-dimensional atom probe. Data clearly show that cementite starts to decompose at the early stage of deformation. This indicates that the driving force of cementite decomposition during plastic deformation is not related to a strong increase of the interfacial energy. Carbon atmospheres were also analysed. They probably result from pipe diffusion of carbon atoms along dislocations pined by Fe3C carbides.Comment: 12 page

Grain boundary segregation in UFG alloys processed by severe plastic deformation

Grain boundary segregations were investigated by Atom Probe Tomography in an Al-Mg alloy, a carbon steel and Armco\trademark Fe processed by severe plastic deformation (SPD). In the non-deformed state, the GBs of the aluminium alloy are Mg depleted, but after SPD some local enrichment up to 20 at.% was detected. In the Fe-based alloys, large carbon concentrations were also exhibited along GBs after SPD. These experimental observations are attributed to the specific structure of GBs often described as "non-equilibrum" in ultra fine grained materials processed by SPD. The grain boundary segregation mechanisms are discussed and compared in the case of substitutional (Mg in fcc Al) and interstitial (C in bcc Fe) solute atoms

On the origin of extremely high strength of ultrafine-grained Al alloys produced by severe plastic deformation

Ultrafine-grained Al alloys produced by high pressure torsion are found to exhibit a very high strength, considerably exceeding the Hall-Petch predictions for the ultrafine grains. The phenomena can be attributed to the unique combination of ultrafine structure and deformation-induced segregations of solute elements along grain boundaries, which may affect the emission and mobility of intragranular dislocations

Evaluation de la fermentation du cacao par le biais de profils de dégradation des protéines

La qualité du cacao est l'une des questions fondamentales pour les fabricants de chocolats fins. On admet maintenant généralement que la qualité est étroitement liée au processus de fermentation. De ptùssants précurseurs d'arôme, principalement des peptides ct des acides aminés, sont produits pendant ce processus par hydrolyse des protéines de stockage issues des cotylédons. Toutefois, actuellement, il n'existe pas de données claires en lien avec le profil protéique d'un cacao fermenté et la qualité du produit. Ces travaux visaient à comprendre si les profils protéiques du cacao fermenté étaient différents selon le stade de fermentation et la variété de cacao avant des essais qui font intervenir une torréfaction du cacao. Dans cette étude, des protéines ont été extraites d'environ une centaine d'échantillons de fèves de cacao provenant de différents stades de fennentation. Les analyses de protéines ont été effectuées par électrophorèse sur gel de polyacrylamide en présence de dodécylsulfate de sodium (SDS-PAGE) sui vie par une coloration et un balayage en transmission à 300 ppp. Les protéines ciblées ont été quantifiées par comparaison de leur volume sur SDS-PAGE avec cel il de SAB. Après deu.x jours seulement de fermentation, une dégradation rapide de la majorité des protéines a été observée. Néanmoins, certaines protéines disparaissaient lentement pendant la fermentation, en particulier celles de faible poids moléculaire, c'est-à-dire inférieur à 25 kDa Entre 80 et 95% disparaissaient après 6 jours de fermentation. L'importance de la diminution dépendait de la variété de cacao et/ou du délai initial avant le commencement de la fermentation. (Résumé d'auteur

Evolutionary Advantage Conferred by an Eukaryote-to-Eukaryote Gene Transfer Event in Wine Yeasts

Although an increasing number of horizontal gene transfers have been reported in eukaryotes, experimental evidence for their adaptive value is lacking. Here, we report the recent transfer of a 158-kb genomic region between Torulaspora microellipsoides and Saccharomyces cerevisiae wine yeasts or closely related strains. This genomic region has undergone several rearrangements in S. cerevisiae strains, including gene loss and gene conversion between two tandemly duplicated FOT genes encoding oligopeptide transporters. We show that FOT genes confer a strong competitive advantage during grape must fermentation by increasing the number and diversity of oligopeptides that yeast can utilize as a source of nitrogen, thereby improving biomass formation, fermentation efficiency, and cell viability. Thus, the acquisition of FOT genes has favored yeast adaptation to the nitrogen-limited wine fermentation environment. This finding indicates that anthropic environments offer substantial ecological opportunity for evolutionary diversification through gene exchange between distant yeast species

Non-equilibrium intermixing and phase transformation in severely deformed Al/Ni multilayers

Al/Ni multilayers have been prepared by repeated folding and cold rolling (F&R) of elemental foils. The thickness of Al and Ni foils is reduced down to less than 50 nm after fifty F&R cycles. Three-dimensional atom probe analyses clearly reveal the presence of supersaturated solid solutions and give the evidence of deformation-induced intermixing. The formation of the solid solutions and their transformation into the Al3Ni phase upon annealing is discussed.Comment: 4 page

Achieving highly strengthened Al-Cu-Mg alloy by grain refinement and grain boundary segregation

An age-hardenable Al-Cu-Mg alloy (A2024) was processed by high-pressure torsion (HPT) for producing an ultrafine-grained structure. The alloy was further aged for extra strengthening. The tensile strength then reached a value as high as ~1 GPa. The microstructures were analyzed by transmission electron microscopy and atom probe tomography. The mechanism for the high strength was clarified in terms of solid-solution hardening, cluster hardening, work hardening, dispersion hardening and grain boundary hardening. It is shown that the segregation of solute atoms at grain boundaries including subgrain boundaries plays a significant role for the enhancement of the tensile strength