Effects of Cr/Ni ratio on physical properties of Cr–Mn–Fe–Co–Ni high-entropy alloys

Physical properties of ten single-phase FCC CrxMn20Fe20Co20Ni40-x high-entropy alloys (HEAs) were investigated for 0 ≤ x ≤ 26 at%. The lattice parameters of these alloys were nearly independent of composition while solidus temperatures increased linearly by ∼30 K as x increased from 0 to 26 at.%. For x ≥ 10 at.%, the alloys are not ferromagnetic between 100 and 673 K and the temperature dependencies of their coefficients of thermal expansion and elastic moduli are independent of composition. Magnetic transitions and associated magnetostriction were detected below ∼200 K and ∼440 K in Cr5Mn20Fe20Co20Ni35 and Mn20Fe20Co20Ni40, respectively. These composition and temperature dependencies could be qualitatively reproduced by ab initio simulations that took into account a ferrimagnetic ↔ paramagnetic transition. Transmission electron microscopy revealed that plastic deformation occurs initially by the glide of perfect dislocations dissociated into Shockley partials on {111} planes. From their separations, the stacking fault energy (SFE) was determined, which decreases linearly from 69 to 23 mJ·m−2 as x increases from 14 to 26 at.%. Ab initio simulations were performed to calculate stable and unstable SFEs and estimate the partial separation distances using the Peierls-Nabarro model. While the compositional trends were reasonably well reproduced, the calculated intrinsic SFEs were systematically lower than the experimental ones. Our ab initio simulations show that, individually, atomic relaxations, finite temperatures, and magnetism strongly increase the intrinsic SFE. If these factors can be simultaneously included in future computations, calculated SFEs will likely better match experimentally determined SFEs

Atom probe contribution to the caracterisation of CIGSe grain boundaries

International audienceAtom Probe Tomography (APT) technique is the only nano-scale-sensitive analytic tool allowing 3D chemical analysis with atomic scale resolution. For long restricted to conductive samples, implementation of ultra fast laser pulsing extend now the field of applications to the analysis of semiconductor materials. In the present study, high efficiency Cu(In, Ga)Se 2 (CIGSe) thin films have been investigated by APT in order to solve interrogations about grain boundaries (GBs) composition. The analyzed CIGSe layers have been grown by co-evaporation on Mo-coated soda-lime glass substrates following the standard 3-stage process and the atom probe tips prepared using a focused ion beam (FIB) equipment. In order to ensure the presence of GB in the small APT investigated volume, location and misorientation of GBs have been determined by electron backscattering scanning diffraction (EBSD) and one GB interface placed close to the edge of the tip. From APT analyses, spatial distribution of CIGSe elements can be imaged at atomic scale; particular attention has been devoted to the composition profiles at the vicinity of the CIGSe GB interface. New results are compared with usual CIGSe GB passivation models. © 2011 IEEE

Atom probe contribution to the caracterisation of CIGSe grain boundaries

International audienceAtom Probe Tomography (APT) technique is the only nano-scale-sensitive analytic tool allowing 3D chemical analysis with atomic scale resolution. For long restricted to conductive samples, implementation of ultra fast laser pulsing extend now the field of applications to the analysis of semiconductor materials. In the present study, high efficiency Cu(In, Ga)Se 2 (CIGSe) thin films have been investigated by APT in order to solve interrogations about grain boundaries (GBs) composition. The analyzed CIGSe layers have been grown by co-evaporation on Mo-coated soda-lime glass substrates following the standard 3-stage process and the atom probe tips prepared using a focused ion beam (FIB) equipment. In order to ensure the presence of GB in the small APT investigated volume, location and misorientation of GBs have been determined by electron backscattering scanning diffraction (EBSD) and one GB interface placed close to the edge of the tip. From APT analyses, spatial distribution of CIGSe elements can be imaged at atomic scale; particular attention has been devoted to the composition profiles at the vicinity of the CIGSe GB interface. New results are compared with usual CIGSe GB passivation models. © 2011 IEEE

Atom probe contribution to the caracterisation of CIGSe grain boundaries

International audienceAtom Probe Tomography (APT) technique is the only nano-scale-sensitive analytic tool allowing 3D chemical analysis with atomic scale resolution. For long restricted to conductive samples, implementation of ultra fast laser pulsing extend now the field of applications to the analysis of semiconductor materials. In the present study, high efficiency Cu(In, Ga)Se 2 (CIGSe) thin films have been investigated by APT in order to solve interrogations about grain boundaries (GBs) composition. The analyzed CIGSe layers have been grown by co-evaporation on Mo-coated soda-lime glass substrates following the standard 3-stage process and the atom probe tips prepared using a focused ion beam (FIB) equipment. In order to ensure the presence of GB in the small APT investigated volume, location and misorientation of GBs have been determined by electron backscattering scanning diffraction (EBSD) and one GB interface placed close to the edge of the tip. From APT analyses, spatial distribution of CIGSe elements can be imaged at atomic scale; particular attention has been devoted to the composition profiles at the vicinity of the CIGSe GB interface. New results are compared with usual CIGSe GB passivation models. © 2011 IEEE

Etude de l’élaboration de matériaux à haute entropie a partir de poudres

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On the atomic structure of an asymmetrical near Sigma=27 grain boundary in copper

The atomic structure of an asymmetrical near Sigma = 27 {525} tilt grain boundary (GB) in copper is determined by coupling high-resolution transmission electron microscopy and molecular dynamics simulation. The average GB plane is parallel to {414} in crystal (1) and {343} in crystal (2). The detailed GB structure shows that it is composed of facets always parallel to {101} and {111} in crystals (1) and (2), respectively. The atomic structure of one facet is described using the structural units model. Each facet is displaced with respect to its neighbours by a pure step, giving rise to the asymmetry of the GB plane orientation. The energy of this asymmetrical GB is significantly lower than that of both the {525} symmetrical and the {11,1,11}/{111} asymmetrical Sigma = 27 GBs. One GB region displays another atomic structure with a dislocation that accounts for the misfit between interatomic distances in the {414} and {343} GB planes

Elaboration d'alliages a composition complexe par fabrication additive

International audienceLe plus souvent, dans les zones de contacts mobiles des centrales nucléaires on utilise un revêtement base cobalt dénommé Stellite®. Il a une bonne tenue à la corrosion et un excellent comportement en situation de frottement. Malheureusement, le cobalt est un élément qui s’active facilement sous flux neutronique par formation de cobalt 60 qui peut alors contaminer le reste du système. Malgré de nombreuses propositions de matériaux substituts sans cobalt (base fer ou nickel), aucune solution ne s’est révélée totalement équivalent en termes de propriétés tribologiques. Les alliages à composition complexe (ACC) sont une nouvelle possibilité de recherche de substituts des alliages base cobalt. A la différence des alliages classiques, les ACC ne possèdent pas d’élément majoritaire, ils sont composés de plusieurs éléments en forte proportion. Si leur microstructure ne comporte qu’une seule phase, l’alliage est dit « à haute entropie ». Afin de réaliser ces ACC, la technique de projection laser est retenue. La présence de plusieurs distributeurs de poudres permet de contrôler la composition des alliages et de la faire varier continument au cours de l’élaboration. Ce procédé de fabrication additive permet de générer rapidement différents ACC et donc d’étudier l’influence de certains éléments sur leurs microstructures et leurs propriétés. Une première sélection d’éléments est proposée en tenant compte du cahier des charges de l’application, des considérations métallurgiques (dont une analyse bibliographique) ainsi que des capacités et limites du procédé. Après définition d’un plan d’expérimentation, plusieurs ACC sont élaborés en faisant varier les paramètres du procédé (puissance, vitesse de déplacement, débit des poudres, …) et la proportion respective des éléments retenus (par exemple Ni, Fe, Cr, Mo, Mn, Al, Ti, V). Ces ACC sont ensuite analysés par microscopie optique, micro-dureté, MEB (électrons secondaires, EDS …), DRX et EBSD. Cela permet de retenir les ACC les plus intéressants pour poursuivre par des essais de frottement sur tribomètre pion (céramique)-disque sous gaz neutre. Une relation entre le comportement en tribologie et la microstructure est établie. Cette étude nous a permis de réaliser une exploration initiale de ces ACC ainsi que de mieux comprendre leur comportement en tribologie. L’étude se poursuit par des tests complémentaires (tenue à la corrosion, essais mécanique…) et l’étude de nouvelles composition

Impact of Annealing Induced Intermixing on the Electronic Level Alignment at the In2S3 Cu In,Ga Se 2 Thin Film Solar Cell Interface

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