Search

The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX—a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.

Surface treatments of Ti-6Al-4V alloys are of utmost importance for biomedical applications since they allow for tribological gain. Here, Ti-6Al-4V disks have been PBII nitrided at either 500, 600, 700 and 800 °C. A set of techniques (XRD, SEM-EDS, EBSD and GDOES) was used to characterize the surface microstructural and chemical changes. Nanoindentation was used to assess the induced changes in terms of mechanical properties. Two types of nitrided domains are revealed. Starting from the surface, a nitride bilayer composed of δ-TiN/ϵ-Ti2N with enhanced surface resistance is supported by an α-Ti(N) solid solution formed at depth. Hardness values peak at 12–14 GPa at the surface, which is almost twice as large as the bulk value (about 7 GPa). For the moderate temperatures used here, a deep (10–15 µm) and strong hardness (14 GPa) enhancement together with a smooth gradient can be achieved.

Instrumented Indentation Testing is applied on a fluoroelastomer so as to get information about the local mechanical response of such a rubbery material. Due to their viscoelasticity, elastomers exhibit a time-dependence, responsible for a variation in their behavior as a function of the stress or strain rate. A few studies highlight modifications of the indentation hardness H and modulus E r when the load function varies. However, these works concern polymers and, to our knowledge, such an investigation has not yet been carried out on elastomeric materials. Results about the influence of the loading-unloading procedure on E r are presented here. They show elastic modulus' variations depending on the chosen protocol's time scale and reported evolutions are consistent with the expected behavior of viscoelastic materials. Furthermore, in preparation of this main study, preliminary verifications were necessary since sources of error are known to distort indentation results. A focus on the microstructure and roughness is presented in this paper and reveals, in particular, a non-negligible improvement of indentation curves (load-displacement hystereses) with an appropriate sample preparation and surface finish. These results have finally been used as a basis for the study of local gradients within a rubber sample. This study revealed a gradient (i.e. an increasing modulus) from the outer part of the sample to the inner one, attributed to thermal effects during the molding.

Residual stresses in thin films and multi-layered coatings fabricated by physical vapour deposition largely affect their mechanical and thermal reliability during operation in numerous fields of applications. By changing the argon working pressure in between each multilayer planar DC magnetron sputter deposition step, it is possible to control the residual stress distribution within coatings. A combination of FIB-DIC ring-core strain analysis, synchrotron XRD analysis based on the sin2(Ψ) method and micro-cantilever deflection analysis is used to reconstruct the in-plane stress state of multilayer coatings at different deposition pressures, with a residual stress depth profile resolution of 50 nm. A clear transition from compressive to tensile residual stresses is observed with an increase of working pressure, with pronounced stress peaks near the substrate-coating interface. These peak stresses resolved by FIB-DIC ring-core analysis exceed the average XRD stress measurements significantly, thus providing a reasonable explanation for multilayer failure. Experimental results are presented and comprehensively discussed in the context of deposition conditions for different thin film applications.

Nanostructured metallic multilayers with carefully designed mechanical and functional properties are omnipresent in cutting edge technological applications. To ensure the mechanical integrity of such coatings, the Mode I critical Stress Intensity Factor KIC is used to quantify their fracture toughness in order to avoid material failure by appropriate design. In this article, we present a novel approach for the KIC determination of thin and ultrathin films on compliant substrate, based on micro-displacement field analysis using Digital Image Correlation within SEM. Using this method, KIC of a Cu/W nano-multilayer with a total coating thickness of 240 nm was determined as K IC = 4.8 ± 0.05 MPa m , showing excellent agreement with the values published for comparable systems in the literature. To verify the validity of the chosen approach, two independent finite element simulations were employed, thus revealing the role and effect of the compliant substrate on the stress and displacement fields arising around the crack tip in thin films.

International audience; L’article introductif analyse les collections sur les pays baltiques / républiques socialistes soviétiques baltes / États baltes de la contemporaine. La région balte est difficilement identifiable dans les collections, du fait de son destin heurté au Vingtième siècle ou du peu d’intérêt qu’on lui porte. Seuls deux grands ensembles documentaires sont abondamment alimentés : l’un concerne les minorités germanophones de la région, l’autre la « question balte » pendant la guerre froide. Cette situation s’explique par des logiques d’acquisition et des enjeux internationaux bien spécifiques.

Hypothesis The poor miscibility of carbon nanotubes (CNTs) in common organic solvents and organic monomers requires their modification by suitable functional (reactive or not) groups prior to their incorporation in thermoplastic polymers. Experiments Dispersion behavior of carbon nanotubes and mechanical properties of various CNT–poly(methylmethacrylate) (PMMA) nanocomposites were investigated. We studied the influence of the surface chemistry through the use of diazonium salts as an elegant and environmentally friendly platform to provide a suitable sidewall functionalization by methyl methacrylate functions. We used either a molecular size functional group through the grafting of methacryloxypropyltrimethoxysilane or a macromolecular size one, consisting in PMMA brushes grown by SI-ATRP in order to study the influence of the length of methacrylate function on the dispersion of CNT in PMMA. Findings The hardness and the elastic indentation modulus of all hybrid films were obtained through nanoindentation measurements and found to increase, using ATRP-modified CNTs, suggesting a better dispersion of CNTs in PMMA due to optimal inorganic–organic interactions promoted by the short chains of PMMA.

Synchrotron X-ray diffraction is a powerful tool to analyse the mechanical behavior of multiphase materials due to its selectivity. Simultaneous stress analysis of both phases of a W/Cu thin multilayer has been performed during a continuous biaxial loading on DiffAbs beamline at SOLEIL synchrotron (France). The use of a 2D detector with a large sample-detector distance is shown to give relatively accurate applied stress analysis even if only a small part of the usual ψ range of the sin2ψ method is considered. The results show the failure of the thin film multilayer while the W components are still under a strong compressive stress state of-3 GPa. It is concluded that the mechanical behavior is in fact mainly governed by the residual stress state.

Nanocrystalline metallic coatings of sub-micron thickness are widely used in modern microelectronic applications. In X-ray diffraction experiments to determine both the residual and applied stresses in nanocrystalline coatings, one difficult challenge that comes up invariably is the determination of the strain-free lattice spacing d. The present study addresses this challenge by using the focused ion beam (FIB) to generate a built-in strain-free reference by patterning (milling) a 50 × 50 μm region of the coating to produce an array of small stress-relieved "islands" ~ 0.8 × 0.8 μm each. Transmission X-ray diffraction setup was used for data collection at DIFFABS beamline (Synchrotron SOLEIL, France). A 150 nm-thick multi-layered W-Cu nano-composite thin film on polyimide (Kapton®) substrate was studied. The samples were loaded incrementally using a compact uniaxial loading device, and micro-beam diffraction data were collected on and away from the reference array. It was shown experimentally that the "island" array remained approximately strain free throughout the experiment, providing an on-board d lattice spacing reference. The changing lattice spacing d in the coating was also monitored away from the array, to deduce the elastic strain evolution during deformation. The results and their implications are presented and discussed. © 2013 Elsevier B.V. All rights reserved.

International audience

In situbiaxial tensile tests within the elastic domain were conducted with W/Cu nanocomposite thin films deposited on a polyimide cruciform substrate using a biaxial testing machine developed on the DiffAbs beamline at the Synchrotron SOLEIL. The mechanical behaviour of the nanocomposite was characterized at the micro- and macroscales using synchrotron X-ray diffraction and digital image-correlation techniques simultaneously. Strain analyses for equibiaxial and non-equibiaxial loading paths were carried out. The results show that the two strain measurements match to within 1 × 10−4in the elastic domain for strain levels less than 0.3% and for both loading paths.

Instrumented indentation mechanics and its applications to ceramics characterisation are described and discussed. Instrumented nanoindentation has become an outstanding tool for characterising surfaces and is routinely used in industry and university. The article reviews important procedures and concepts that have proved to be very useful to analyse the contact response of ceramics (elastic–plastic loading, indentation strains and stresses, crack generation, composite response of coated pieces). Examples are used to illustrate the very wide range of studies that can be carried out.

International audience; No abstract available

International audience; In Latvia, the transition has gradually led to the state’s withdrawal from the housing sector since the mid-1990s. Housing reforms have encountered obstacles that are retarding the renewal of the stock of housing. A very particular system has thus emerged that, in many respects, stands apart from what exists in neighboring lands. This study of the transition in the Latvian housing sector is based on experiences in seven municipalities and the Ministry of the Economy. It analyzes modifications in the policies conducted and their failures, and assesses privatization. A conception of public housing is presented along with the system for managing housing and keeping it in repair.; En Lettonie, la transition dans le secteur du logement est animée par le dé-sengagement progressif de l'État depuis le milieu des années 1990. La mise en oeu-vre des politiques réformatrices du logement a rencontré des obstacles qui freinent aujourd'hui la rénovation du parc et a donné naissance à un système du logement bien particulier, se distinguant à maints égards de celui des pays voisins. L'auteur propose ici, en se fondant sur l'expérience de sept municipalités et du ministère de l'Économie, une étude du système letton du logement en transition. Celle-ci com-prend une analyse de l'évolution des politiques menées et de leurs échecs, notam-ment un bilan de la privatisation, et une présentation de la conception du logement social ainsi que du système de gestion et d'entretien de l'habitat.

National audience; The local mechanical response of a fluoroelastomer is presented through nanoindentation results. It is well known that elastomers properties aretime-dependent and thus are influenced by the experimental protocol parameters such as the maximum applied load or loading rates. One should consider with great care this time-dependence in the case of nanoindentation tests as it can be in the case of global characterizations. The aim of this study is to determine the influence of the time-dependence during nanoindentation characterization of elastomers. In fine, these investigations should lead to a robust methodology, capable of giving quantitative measurements of the local mechanical properties of industrial products made of elastomers. Thus, this paper draws up a description of the nanoindentation technique applied on elastomers materials and discusses the results which are clearly dependent on the way they are driven. Finally, information provided by this study allowed the technique to be applied on a multilayered composite rubber/polymer, which proved the relevance of the technique by detecting properties gradients within the composite.; La réponse mécanique locale d’un fluoroélastomère est présentée au travers de résultats denanoindentation. Les propriétés des élastomères présentent notamment une dépendance à la vitesse desollicitation et sont ainsi impactées par les variables du protocole expérimental choisies, telles que laforce maximale appliquée ou les vitesses de chargement. Cette caractéristique, intrinsèque à ce type de matériaux, est considérée avec soin dans le cadre d’essais à échelle globale et doit, au même titre, faire l’objet d’une attention particulière lors d’essais de nanoindentation. L’objectif de cette étude est d’appréhender l’impact de la dépendance au temps des élastomères lors de leur caractérisation en nanoindentation. Infine, les investigations doivent pouvoir mener à une méthodologie robuste capable de donner des mesures quantitatives des propriétés mécaniques locales d’élastomères de pièces réelles industrielles. Ce papier dresse donc une description de la technique de nanoindentation appliquée aux élastomères et discute les résultats qui apparaissent clairement dépendants de la manière dont les essais sont conduits. Enfin, les éléments apportés par cette prospection ont été appliqués à la caractérisation d’un composite multicouche caoutchouc/polymère. Cette étude applicative a prouvé l’aptitude de la nanoindentation à détecter desgradients de propriétés au sein du composite.

International audience; The early occurrence of intentional heat treatment of silica rocks has recently become a key element in the discussion about the cultural modernity of prehistoric populations. Lithic vestiges are the only sources that remain of this process and the understanding of the material's properties and transformations are essential for reconstructing the conditions and parameters applied during heat treatment. Several models of the structural transformations upon heating have been proposed in the current literature. These models are often contradictory and do not account for the most recent structural and mineralogical data on chalcedony. In order to propose a new model, we elaborated an experimental procedure and applied different techniques involving infrared spectroscopy, solid state NMR, X-ray diffraction and electron microscopy. The results show that the major transformation to happen is the loss of silanole (SiOH) and the creation of new Si-O-Si bonds according to the reaction: Si-OH HO-Si -> Si -O-Si + H2O. This reaction starts between 200 degrees C and 300 degrees C and causes an increase in the hardness of the rocks. The maximal annealing temperature and the ramp rate are the functions of the ability of the structure to evacuate newly created H2O and depend on the size of the specimen and the volume of its porosity. These results also show that the annealing duration at maximum temperature can be relatively short (

International audience; The development of new devices has created needs of precision, conformal at the atomic level deposition of high quality thin film materials. In the last years, Atomic Layer Deposition (ALD) has received much interest as a potential deposition method for advanced thin film structures. ALD presents several advantages: the film is excellently conformal and reproducible; the film thickness depends only on the number of reaction cycles, which makes the thickness control accurate and simple; the film can be deposited onto all kind of substrates. Because of the process slowness, layer thickness is generally less than 100 nm. This makes more difficult to study all characteristics of the coating. Thin layers deposited onto bulk substrates are generally in tensile or compressive stress state, which may significantly affect physical properties and possibly compromise their lifetime. To determine the residual stress it is mandatory to know the elastic constants that may also depend on the microstructure of the layers and thus the deposition process.In this work, 2D X-ray diffraction (XRD2) in combination with in situ tensile testing has been applied for the first time to measure elastic properties of TiO2 anatase films obtained by ALD. Experimental conditions, the tensile stage being installed in a laboratory micro-diffractometer equipped with a 2D image-plate detector, and the information that can be extracted from 2D diffraction patterns will be discussed. Based on these preliminary results, synchrotron radiation beam time has been allocated to study elastic properties of these thin films. The advantages and disadvantages of the proposed laboratory equipment, with respect to the synchrotron beam lines, are discussed.

Zirconium oxynitride thin films were deposited by dc reactive magnetron sputtering. A zirconium metallic target was sputtered in an Ar + N2 + O2 atmosphere. Argon and nitrogen flow rates were maintained constant whereas oxygen was pulsed during the deposition, implementing the reactive gas pulsing process (RGPP). A constant pulsing period T = 3 s was used following an exponential periodic signal versus time. The introduction time of oxygen was systematically changed from 17% to 83% of the period. The RGPP allowed the synthesis of ZrOxNy films with tuneable metalloid concentrations adjusting the introduction time of the oxygen. Composition and structural variations associated with mechanical, optical and electrical properties exhibited a smooth transition, from metallic-like characteristics, typical of the fcc-ZrN phase, to semi-conducting behaviour corresponding to a mixture of orthorhombic-Zr3N4(O) and γ -Zr2ON2 crystalline phases., Fundação para a Ciência e Tecnologia (FCT) - PTDC/CTM/69362/2006.

The mechanical behavior of nanostructured stratified W/Cu composites prepared by ion beam sputtering has been investigated using a method combining X-ray diffraction and tensile testing. Tests were performed on a synchrotron light source to analyze the elastic response of the tungsten phase. Three different microstructures have been analyzed: the specimen composed of the thinner tungsten layers reveals an elastic behavior different from the one expected assuming bulk elastic constants. However, Transmission Electron Microscopy (TEM) and Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) measurements reveal discontinuities in the copper layers. As the strain in the related copper clusters as well grains boundary contributions are not experimentally accessible, atomistic calculation are of utmost importance. Polycrystalline materials have already been constructed through the Voronoï method and thanks to TEM observations. Atomistic simulation and calculation are underway to validation.

Fluorinated hybrid organic-inorganic silicates (ORMOSIL) thin films display exceptional mechanical properties in terms of both hardness and elastic modulus that can be finely tuned by varying the angular velocity of the spin coating process. Hence, as traditional alkyl-modified silica xerogels generally show poor mechanical behavior, these materials offer a solution to a major limitation to applicability of ORMOSIL-based films.

Understanding the mechanical behaviour of nano-structured thin films in relation to their structure, in particular to the grain size, is of high importance for the development of technological applications. Model nanometric multilayer W/Au systems exhibiting different structures are elaborated. These films are supported by a (thin) polyimide substrate. Films mechanical response is characterized experimentally by tensile tests carried out in-situ in a X-ray diffractometer installed on a synchrotron source. X-ray diffraction in transmission geometry has been used to study the deformations of both phases as a function of applied load. This geometry has been developed in the aim of optimizing the experiment time.

The mechanical behavior of W/Cu multilayers with a period of 24 nm and a 1/3 W/Cu thickness ratio prepared by magnetron sputtering was analyzed using a method combining X-ray diffraction and tensile testing. Tests were performed both with a conventional and a synchrotron light source to analyze the elastic response of the system. Comparison between the strain-load curves obtained in both experimental conditions and estimated curves clearly shows that high quality synchrotron measurements are a preliminary condition for size-effect studies. Moreover, cyclic tests were used to determine the elastic domain of each material and compare their mechanical responses. Plastic strain was observed in copper while tungsten layers were still elastically strained until cracks appeared.

Du 10 au 12 decembre 2014, a l’institut Charles Sadron (UPR 22 CNRS, Strasbourg), s’est tenu le colloque Indentation 2014, deuxieme edition de ce congres francophone a la suite de celui de 2012 qui avait ete organise par le laboratoire LTDS a l’Ecole Centrale de Lyon. Le colloque a reuni tous les scientifiques utilisateurs avances des techniques d’indentation instrumentee. Ces techniques d’indentation statique ou dynamique (rayure) sont de plus en plus utilisees a l’echelle industrielle comme outil de caracterisation des surfaces de materiaux fonctionnalises. Ces techniques recentes ne sont pas encore au stade des essais conventionnels de caracterisation des materiaux massifs (essais de traction, essais de compression ou encore de cisaillement). C’etait justement l’objet du colloque Indentation 2014 : faire un etat des lieux des recherches fondamentales (comprehension de la mecanique complexe des essais d’indentation et de rayure) et appliquees (informations deduites des essais sur des materiaux nouveaux ou innovants) en cours dans le domaine. Durant ce colloque, qui a reuni 70 participants issus des equipes francaises possedant des equipements instrumentaux et/ou des moyens numeriques dedies aux techniques d’indentation, 25 presentations orales et environ une vingtaine de posters ont ete presentes. L’ensemble de ces travaux presentes, lors de 5 sessions a suscite de nombreuses discussions et echanges entre les participants. Deux conferenciers Mr. Stephane Andre (LEMTA) et Mme Trunfio Sfarghiu (LaMCoS) ont ete invites pour presenter respectivement les enjeux de la metrologie contemporaine et la spectroscopie de forces atomiques pour l’analyse mecanique et tribologique des contacts biologiques. Nous presentons dans ce numero thematique, un ensemble d’articles issus d’une selection de contributions au colloque, publies apres un processus d’evaluation et de revision. Ces articles offrent un apercu de toutes les thematiques abordees au cours du colloque. L’ensemble du numero regroupe des travaux fondamentaux et appliques et permet de faire un point sur des sujets d’actualite dans le domaine de l’indentation. Le lecteur y trouvera des travaux couvrant un large spectre de materiaux. Differentes analyses des comportements elastique, fragile et ductile investiguees aux echelles pertinentes sont presentees et discutees. Les editeurs (H. Pelletier et E. Le Bourhis) tiennent a remercier les membres du comite d’organisation (A. Rubin, V. Le Houerou, J. Krier, T. Roland, L. Jacomine, D. Favier, H. Pelletier, C. Gauthier) pour la tenue de ce colloque, ainsi que les membres du comite scientifique du groupe indentation multiechelle (E. Barthel, S. Benayoun, D. Chicot, J.-P. Guin, V. Keryvin, E. Le Bourhis, J.-L. Loubet, G. Mauvoisin, H. Pelletier, http://www.sf2m.asso.fr/ CommissionsThematiques/Indentation.htm) qui ont accepte de rapporter chacun sur plusieurs articles publies dans cet ouvrage.

Le colloque Comportements mecaniques s’est deroule du 24 au 28 novembre 2014 dans le cadre de la conference Materiaux 2014 a Montpellier (http://www.sf2m.asso. fr/FFM_2014/mat2014/indexMat2014.html). Il a permis de reunir une communaute de chercheurs academiques et industriels, travaillant dans le domaine de la Mecanique des Materiaux, afin de discuter des dernieres avancees et d’echanger sur les pratiques et les perspectives. Ce colloque a ete consacre aux etudes menees sur la description du comportement mecanique de materiaux tres divers (polymeres, verres, alliages metalliques, mousses, ceramiques, geomateriaux, milieux granulaires, suspensions colloidales, biomateriaux, etc.), en se fondant sur leur microstructure et/ou leurs mecanismes de deformation, d’endommagement et de rupture. Cette problematique inclut aussi bien l’elaboration (mise en forme, compaction, etc.) que la tenue en service normal et accidentel d’un materiau sous des chargements thermomecaniques varies. Les types de comportement abordes sont de natures tres diverses : elastique fragile, viscoelastique, hyperelastique, elastoviscoplastique, endommageable. Le colloque a accueilli plus de cent communications presentant des travaux experimentaux, numeriques et theoriques sur les relations microstructure – mecanismes locaux – proprietes effectives . Il s’est articule autour de huit sessions thematiques portant sur : les approches probabilistes et l’homogeneisation, l’endommagement et la rupture, les sollicitations dynamiques, la rheologie des milieux granulaires, la mecanique des polymeres, la metallurgie mecanique, les interfaces dans les milieux solides et l’etude des comportements aux echelles micro et nanometriques. Nous presentons dans ce numero thematique, un ensemble d’articles issus d’une selection de contributions au colloque, publies apres un processus d’evaluation et de revision. Ces articles offrent un apercu de toutes les thematiques abordees au cours du colloque. L’ensemble du numero regroupe des travaux fondamentaux et appliques et permet de faire un point sur des sujets d’actualite dans le domaine de la Mecanique des Materiaux. Le lecteur y trouvera des travaux couvrant un large spectre de materiaux. Differentes modelisations des comportements elastique, fragile et ductile investiguees aux echelles pertinentes sont presentees et discutees. Les editeurs (R. Brenner et E. Le Bourhis) tiennent a remercier les organisateurs de Materiaux 2014 pour la programmation de ce colloque, les coordonnateurs des sessions thematiques (N. Bahlouli, R. Bargellini, N. Billon, R. Brenner, N. Carrere, O. Castelnau, J.P. Couzinie, J.Y. Delenne, B. Fayolle, L. Guillaumat, P. Ienny, J. Laverne, E. Le Bourhis, M. Lemaire, S. Mercier, Y. Monerie, D. Piot, F. Radjai, I. Raoult, M. Sauzay, H. Trumel, P. Viot, F. Willot) ainsi que les rapporteurs qui ont accepte d’expertiser les articles publies dans ce numero.

Cet article illustre la mise en œuvre d’essais biaxiaux de films minces d’epaisseur nanometrique sur supports souples (polymeres). Une machine biaxiale a ete developpee dans ce but et est situee au sein de la ligne DiffAbs du synchrotron Soleil. Le chargement de films minces est associe a des techniques de mesure de deformation, comme la diffraction des rayons X et la correlation d’image numeriques. Nous montrons que cet ensemble instrumental permet de sonder le comportement mecanique du film mince, de l’elasticite a la rupture, avec en supplement des indices sur les mecanismes de deformation.

The poor miscibility of carbon nanotubes (CNTs) in common organic solvents and organic monomers requires their modification by suitable functional (reactive or not) groups prior to their incorporation in thermoplastic polymers. We studied the influence of the functionalization of the surface of CNTs on their miscibility in poly(methyl methacrylate), following two main strategies: (i) the covalent grafting of hydrolyzable Si(OEt)3 groups on oxidized CNTs and (ii) the non-covalent adsorption of a polycation on pristine CNTs, allowing for further reactions by the sol–gel process. The mechanical properties of CNT/polymer-based nanocomposite thin films were studied using the nanoindentation technique. The hardness and the elastic indentation modulus were found to improve using modified CNTs, with more sensitivity observed on the elastic response.