High temperature elasticity and viscosity of GexSe1-x glasses in the transition range

International audienceThe viscous-flow behavior and temperature dependence of the elastic moduli of chalcogenide glasses from the germanium-selenium system were studied by means of homemade high-temperature indentation setup and resonant-frequency technique (1-10 kHz), respectively, for temperatures between 0.8 and 1.2×Tg. The softening rates, both in the elastic and in the viscous-flow regimes, were correlated to network destructuration or reorganization events in the light of previously reported high-temperature neutron-scattering data. The concomitant change of Poisson's ratio (ν) and the thermodynamic parameters of the thermally activated viscous-flow process were characterized and provide a new basis for the understanding of the sources for the softening in the transition range. The temperature dependence of ν suggests weak changes of the network cross-linking degree at large Ge contents. On the contrary, in the case of a-Se, a steep fragmentation of the structural units is inferred from the ν(T) data, and the flow process is accompanied by a huge entropy change (activation entropy at saddle point). The entropy contribution at Tg (Tg ×dSa) represents more than 50% of the activation enthalpy for flow (dHa) and increases with the selenium content. Hence the free activation energy (dGa) is much smaller than apparent activation energy as derived from viscosity data

Modeling of Young's modulus variations with temperature of Ni and oxidized Ni using a magneto-mechanical approach

International audienceThin films and coatings are usually used to give functional properties to the surface of the underlying substrate but are never seen as load bearing due to a very low film to substrate thickness ratio. However, this ratio can increase in some specific domains (such as transportation), where the weight reduction is a high stake. This study deals with the influence of the thermally grown oxide (TGO) NiO on the evolution of the elastic modulus of nickel with temperature. For pure nickel, the Young's modulus evolves non-linearly with temperature, from room temperature up to 360°C, corresponding to the Curie temperature of nickel. The amplitude of these variations can be drastically reduced with the presence of the NiO TGO. The purpose of this study is to propose a modeling of these phenomenon using magneto-mechanical approach. A first analytical modeling takes the change of the saturation magnetization, of the initial anhysteretic susceptibility and of the maximal magnetostriction with a relaxation of magneto-crystalline anisotropy concomitant to increasing temperature, into account. The second modeling is a numerical modeling giving the average behavior of a representative volume element. It allows a continuous description of the change with temperature of the Young's modulus and a clear interpretation of the effect of a coating. This gives an insight for future promising applications

Additive layer manufacturing of titanium matrix composites using the direct metal deposition laser process

Titanium Matrix Composites (TMC's) containing various volume fractions of (TiB+TiC) particles have been deposited from powder feedstocks consisting of a blend of pre-alloyed (Ti-6Al-4V+B4C) powders, using the direct metal deposition (DMD) laser process and the in-situ chemical reaction 5Ti+B4C→4TiB+TiC. Process optimization has allowed to obtain a homogeneous distribution of tiny TiB whiskers within the Ti-6Al-4V α/β matrix, with a full solubilization of C for low B4C contents (0.5 wt% and 1.5 wt%), and the formation of a small amount of globular TiC particles at higher B4C content (3%). Comparisons with Ti-6Al-4V DMD walls revealed a substantial grain refinement on TMC's due to enhanced grain nucleation on TiB whiskers, even for low B4C contents. Last, mechanical investigations indicated an increase of 10–15% of Vickers hardness, and a constant 10% increase of Young modulus on a large temperature range (20–600 °C) for all B4C conten

Atomic Species Associated with the Portevin–Le Chatelier Effect in Superalloy 718 Studied by Mechanical Spectroscopy

In many Ni-based superalloys, dynamic strain aging (DSA) generates an inhomogeneous plastic deformation resulting in jerky flow known as the Portevin--Le Chatelier (PLC) effect. This phenomenon has a deleterious effect on the mechanical properties and, at high temperature, is related to the diffusion of substitutional solute atoms toward the core of dislocations. However, the question about the nature of the atomic species responsible for the PLC effect at high temperature still remains open. The goal of the present work is to answer this important question; to this purpose, three different 718-type and a 625 superalloy were studied through a nonconventional approach by mechanical spectroscopy. The internal friction (IF) spectra of all the studied alloys show a relaxation peak P718 (at 885 K for 0.1 Hz) in the same temperature range, 700 K to 950 K, as the observed PLC effect. The activation parameters of this relaxation peak have been measured, Ea(P718){\thinspace}={\thinspace}2.68{\thinspace}{\textpm}{\thinspace}0.05 eV, $\tau$0{\thinspace}={\thinspace}2{\textperiodcentered}10-15 {\textpm} 1 s as well as its broadening factor $\beta${\thinspace}={\thinspace}1.1. Experiments on different alloys and the dependence of the relaxation strength on the amount of Mo attribute this relaxation to the stress-induced reorientation of Mo-Mo dipoles due to the short distance diffusion of one Mo atom by exchange with a vacancy. Then, it is concluded that Mo is the atomic species responsible for the high-temperature PLC effect in 718 superallo

Etude par frottement interieur haute temperature des defauts structuraux dans le silicium monocristallin

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude de Bonamia Ostreae. Essais d'infestations expérimentales

L'ostréiculture, depuis une dizaine d'années, subit de graves crises dues à des épizooties successives. La première, causée par Marteilia refringens (1969 à 1975), n'a pas atteint les centres vitaux de l 'ostréiculture . La deuxième, due à Bonamia ostreae, mise en évidence en juin 1979 à l'Ile Tudy, touche presque tous les centres ostréicoles bretons (captage, élevage, affinage) , réduisant considérablement la production (- de 3 000 t en 1981) . Dans le cadre de l'étude de cette maladie, nous avons réalisé des essais d' infestations.Les trois techniques de contamination employées sont : la méthode de juxtaposition (proximiy method) , la méthode des broyats ( feeding method) et l'intervention d'un hôte intermédiaire. Pour cela, nous avons réparti des huîtres et des crabes (Careinus maenas) de différentes origines dans 18 aquariums. Cet élevage est couplé avec une culture de phytoplancton pour l'alimentation des huîtres. Ce n'est qu'au terme du sacrifice final que nous avons constaté macroscopiquement (observation de lésions branchiales) et microscopiquement la contamination des huîtres saines par des huîtres de zonesparasitées (méthode de juxtarosition) . L'évaluation des mortalités, relevées quotidiennement a permis aussi de mettre effectivenent en cause Bonamia ostreae dans les mortalités observées sur parcs. Le rôle de la température et celui du  crabe n'ont cependant pas pu être dégagés.L'ostréiculture, depuis une dizaine d'années, subit de graves crises dues à des épizooties successives. La première, causée par Marteilia refringens (1969 à 1975), n'a pas atteint les centres vitaux de l'ostréiculture. La deuxième, due à Bonamia ostreae, mise en évidence en juin 1979 à l'Ile Tudy, touche presque tous les centres ostréicoles bretons (captabe, élevage, affinage), réduisant considérablement la production (-de 3000 t en 1981). Dans le cadre de l'étude de cette maladies, nous avons réalisés des essais d'infestations. Les trois techniques de containation employées sont : la méthode de justaposition (proximity method), la méthode des broyats (feeding method) et l'intervention d'un hôte intermédiaire. Pour cela, nous avon réparti des huîtres et des crabes (Carcinus maenas) de différents origines dans 18 aquariums. Cet élevage est couplé avec une culture de phytoplancton pour l'alimentation des huîtres. Ce n'est qu'au terme du sacrificie final que nous avons constaté macrospiquement (obserations de lésions branchiales) et microscopiquement la contamination des huîtes saines par des huîtes de zones parasitées (méthode de juxtaposition). L'évaluation des mortalités, relevées quotidienneemnt, a pemis aussi de mettre effectivement en caus

Monitoring high performance networks in large-scale clusters

International audienceThe number of large-scale clusters is rising. They are included into Grids or become key components o f large structures. As more users and projects rely 071 HPC clusters, high availability and security are requirements for a fast growing adoption and use. I n this paper, ute focus o n high performance networks. All HPC clusters are built o n top of them. We demonstrate that classical instrumentation are ineficient in HPC environment, they do not scale or cause a significant loss of performance. Based 071. this fact, we highlight clusters properties: nodes have assigned roles and are coupled at various levels. Moreover, we study the main characteristics of resource usage for each type of node and propose a n instrumentation that can be effectively deployed. It results in fine-grained mechanisms adapted to system architecture and performance constraints.. Relevant information is collected over time. Two properties are verified online and dynamically: coherency and containment. Each induces a type of verification and both aim at reducin,g recovery time from failure and security risk of a whole cluster. We illustrate our. rnethodology o n QsNet network and provide a way t o increase safety of high performance networks and clusters