Novel Co 20 Cr 15 Fe 26 Mn 17 Ni 22 ultra-fine grained high-entropy alloy

International audienceIn a non-equiatomic HEA from CoCrFeMnNi family, so-called A3S® alloy (austenitic superstainless steel), exceptional mechanical properties are observed. High yield strength (800 MPa) associated with significant elongation to fracture (35 %) and a stable austenitic paramagnetic structure (down to LN2 temperature) may be obtained in hot forged materials. Mechanical resistance (YS) of A3S is at least 200 MPa higher than that measured in equiatomic alloy (EA) of the same family. These properties come from a nanostructure, easily formed in the material after classical hot thermomechanical treatment (forging). Yet, mechanical resistance of A3S decreases strongly after a post-forging high temperature annealing: in this state, identical behaviors of A3S and EA are noticed. Effects of thermal conditions of forging and recrystallization annealing have been investigated in A3S. Only slight effect of temperature of forging (between 900 and 1100°C) has been shown. Surprising effects of recrystallization annealing have been found. Low temperature (up to 600°C for 48h) treatment leads to recrystallization with formation of fine (1 µm) grains. At higher temperatures (700-1100°C), recrystallization is blocked: only recovery followed by grain growth and formation of numerous twins is observed. Moreover, in this state, very high density of dislocations is conserved: they present ordered configurations with alignments in {111} planes. Formation of twins has major effect on mechanical behavior of both A3S and EA. Their absence stabilizes nanostructures and leads to high YS values while decrease of YS is accompanied by twins presence. Relative difficulty to form these defects in A3S (as compared to EA) is explained by high value of stacking fault energy, evaluated from TEM measurements of dislocations dissociation. Moreover, strong dependence of SFE on temperature has been shown: its lower value at high temperatures is in agreement with numerous twins observed

Identification des propriétés morphologiques et hygrothermiques hétérogènes de nouveaux composites hautes performances soumis à des cycles de vieillissement thermo-hygro-mécaniques

Les nouveaux renforts NCF (Non Crimp Fabrics) sont adaptés aux procédés RTM (Resin Transfer Moulding) ou RIM (Resin Infusion Moulding) et permettent d élaborer des structures aéronautiques complexes et de grande taille. Cependant, la présence de la couture peut conduire à une morphologie spécifique hétérogène du matériau avec un réseau 3D de zones riches en résine. Ces dernières, sous cycles de vieillissement hygrothermiques, sont à l origine d un état spécifique de fissuration. Ainsi, le présent travail se concentre sur la caractérisation morphologique et la fissuration d une famille particulière des NCF - NC2 (Non Crimp New Concept), soumis au vieillissement hygrothermique cyclique. Pour cela, des cycles accélérés de vieillissement sont définis, diverses méthodes de caractérisation sont utilisées et différentes variables représentatives sont introduites. Au sujet de la morphologie du matériau, une hétérogénéité multi-échelles a été visualisée en surface et dans l épaisseur en effectuant des coupes sous microscope 2D et de la reconstruction volumique sous tomographie 3D à RX. En ce qui concerne la fissuration hygrothermique, son initiation et son développement ainsi que sa morphologie ont été étudiés. L influence de la morphologie et des paramètres de chargement au cours des cycles a été identifiée. De plus, afin de maîtriser le comportement des zones riches en résine, un couplage thermique/hygrothermique-mécanique à différents états de vieillissement du matériau a été décrit finement par des mesures de champs. Enfin, la tenue mécanique du matériau vieilli a été étudiée.Stitched multiaxial laminates NCF (Non-Crimp Fabric) are potential candidate materials as new high performance preforms for manufacturing complex and large aeronautical composite structures by RTM (Resin Transfer Moulding) or infusion processes. Stitching within the preform leads to a particular morphology including 3D resin-rich regions and to a specific crack network developed in the bulk of the laminate when this is subjected to hygrothermal ageing cycles. The present work focuses on the characterization of the morphology and the crack development in a particular family of NCF - NC2 (Non Crimp New Concept) subjected to hygrothermal cycling. For this purpose, different accelerated thermal/hygrothermal ageing cycles were defined, various characterisation methods were adopted and representative variables were introduced. Regarding the structural morphology, a multi-scale heterogeneity of the NC2 could be visualized on the surface and through the thickness by optical microscopy as well as by the non-destructive volumetric analysis of X-Ray tomography. Regarding hygrothermal cracking, its initiation, its development and its morphology were studied. The influence of the morphology and the role of loading parameters on crack development were identified. Furthermore, for a better control of resin-rich region behaviour, the thermal/hygrothermal-mechanical coupling at different ageing states was investigated by full-field image correlation. Finally, the mechanical strength of the aged material was determined.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

Neuroinflammatory processes are augmented in mice overexpressing human heat-shock protein B1 following ethanol-induced brain injury

Background: Heat-shock protein B1 (HSPB1) is among the most well-known and versatile member of the evolutionarily conserved family of small heat-shock proteins. It has been implicated to serve a neuroprotective role against various neurological disorders via its modulatory activity on inflammation, yet its exact role in neuroinflammation is poorly understood. In order to shed light on the exact mechanism of inflammation modulation by HSPB1, we investigated the effect of HSPB1 on neuroinflammatory processes in an in vivo and in vitro model of acute brain injury. Methods: In this study, we used a transgenic mouse strain overexpressing the human HSPB1 protein. In the in vivo experiments, 7-day-old transgenic and wild-type mice were treated with ethanol. Apoptotic cells were detected using TUNEL assay. The mRNA and protein levels of cytokines and glial cell markers were examined using RT-PCR and immunohistochemistry in the brain. We also established primary neuronal, astrocyte, and microglial cultures which were subjected to cytokine and ethanol treatments. TNF alpha and hHSPB1 levels were measured from the supernates by ELISA, and intracellular hHSPB1 expression was analyzed using fluorescent immunohistochemistry. Results: Following ethanol treatment, the brains of hHSPB1-overexpressing mice showed a significantly higher mRNA level of pro-inflammatory cytokines (Tnf, Il1b), microglia (Cd68, Arg1), and astrocyte (Gfap) markers compared to wild-type brains. Microglial activation, and 1 week later, reactive astrogliosis was higher in certain brain areas of ethanol-treated transgenic mice compared to those of wild-types. Despite the remarkably high expression of pro-apoptotic Tnf, hHSPB1-overexpressing mice did not exhibit higher level of apoptosis. Our data suggest that intracellular hHSPB1, showing the highest level in primary astrocytes, was responsible for the inflammation-regulating effects. Microglia cells were the main source of TNF alpha in our model. Microglia isolated from hHSPB1-overexpressing mice showed a significantly higher release of TNF alpha compared to wild-type cells under inflammatory conditions. Conclusions; Our work provides novel in vivo evidence that hHSPB1 overexpression has a regulating effect on acute neuroinflammation by intensifying the expression of pro-inflammatory cytokines and enhancing glial cell activation, but not increasing neuronal apoptosis. These results suggest that hHSPB1 may play a complex role in the modulation of the ethanol-induced neuroinflammatory response.Peer reviewe

Accurate strain determination from digital image correlation of Laue diffraction spots

International audienc

Influence of phase contrast and detector resolution on the segmentation of tomographic images containing voids

International audienceAn experimental and numerical tomographic study on the influence of lateral beam coherence and limited detector resolution on the size of voids in copper is presented. Several scans of the same sample were performed at ID15A of ESRF under pink beam conditions and different sample-detector distances. The tomographic images were segmented using a gradient based method and then the same voids appearing in subsequent volumes were identified through image-correlation. It was found that the segmented void size is smaller at short detector distances, but it saturates at values of about 160-200 mm. Simulations show that the phase contrast available at larger distances enhances the intensity gradient at void-matrix interfaces leading to a proper segmentation if gradient based algorithms are used. For distances involved in the present experiment the true size of voids with diameters in the 4.7-12 mu m range is not altered by phase contrast effects. The smaller apparent void size (by about 15-20%) obtained at short distances (20-50 mm) is a result of low signal to noise ratio of the corresponding reconstructions

On the calibration of high-energy X-ray diffraction setups. II. Assessing the rotation axis and residual strains

International audienceThe calibration of high-energy X-ray diffraction setups using an area detector and a rotation axis is discussed. The characterization of the tilt and spatial distortions of an area detector was discussed in part one of this series [Borbely, Renversade, Kenesei & Wright (2014). J. Appl. Cryst. 47, 1042-1053]. Part II links the detector frame to the laboratory frame comprising an additional rotation axis and introduces a general diffractometer equation accounting for all sources of misalignment. Additionally, an independent high-accuracy method for the evaluation of the crystallographic orientation and cell parameters of the undeformed reference crystal is presented. Setup misalignments are mainly described in terms of a residual strain tensor, considered as a quality label of the diffractometer. The method is exemplified using data sets acquired at beamlines ID11 (European Synchrotron Radiation Facility) and 1-ID (Advanced Photon Source) on Al and W single crystals, respectively. The results show that the residual strain tensor is mainly determined by the detector spatial distortion, and values as small as 1-2 x 10(-4) can be practically achieved. (C) 2014 International Union of Crystallograph

Evaluation of intragranular strain and average dislocation density in single grains of a polycrystal using K-map scanning

International audienceQuick scanning X-ray microscopy combined with three-dimensional reciprocal space mapping was applied to characterize intragranular orientation and strain in a single grain of uniaxially deformed Al polycrystal. The strain component perpendicular to the direction of the applied tensile load was found to be very heterogeneous with high compressive and tensile values in the grain interior and near two grain boundaries, respectively. The distribution of the magnitude of diffraction vectors indicates that dislocations are the origin of the strain. The work opens new possibilities for analysing dislocation structures and intragranular residual stress/strain in single grains of polycrystalline materials

Impact of ink synthesis on processing of inkjet-printed silicon nanoparticle thin films: A comparison of Rapid Thermal Annealing and photonic sintering

International audienceInkjet printing has a high potential for cost reduction in solar cell and thermoelectric industry. This study demonstrates that silicon thin films can be produced by inkjet-printing of silicon nanoparticles followed by subsequent drying and annealing steps. Ink formulation is crucial for the sintering of the silicon nanoparticles and control of the microstructure at low temperature. Upon heating, the microstructure is modified from porous layer made of juxtaposed silicon nanoparticles to denser layer with coarser grains. This evolution is monitored by scanning electron microscopy and by micro-Raman spectroscopy, which offer a fast and precise characterization of the microstructure and chemical composition of thin films. Above a threshold temperature of 800 degrees C cracks appear within thin film and substrate because of the stress induced by the oxidation of the surface. An innovative sintering method, photonic annealing, is studied in order to reduce both oxidation and stress in the thin films as well as reducing processing time. Evolution of the thermal conductivity is performed by micro-Raman spectroscopy and can be tailored in a large range between similar to 1 and similar to 100 W.m(-1).K-1 depending on the sintering method and atmosphere. Therefore control of the microstructure evolution with applied annealing process allows tailoring of both microstructure and thermal conductivity of the silicon thin films. (C) 2014 Elsevier B.V. All rights reserved

Orientation dependent recovery in strongly deformed Al-0.1%Mn crystals

International audienceSingle crystals of Al-0.1%Mn have been channel-die compressed to a true strain of 2.3 and their recovery behaviour at 240-320 degrees C investigated by microhardness measurements, EBSD microtexture mapping and X-ray line broadening analysis. The crystal orientations are the nominally stable Goss {110}, brass {110} and S {123}. For all three orientations the microhardness decreases with a logarithmic time dependency but the instantaneous recovery rates of the Brass oriented crystals are systematically lower than those of the other two orientations by a factor of about 2. The dislocation densities decrease rapidly in the first stages of recovery (<1 min) by dislocation dipole annihilation and more slowly thereafter. In the Goss and S orientations the later stage of recovery is due to sub-grain growth. The orientation dependency is ascribed to the relatively low misorientations developed by plastic straining in the Brass crystals (average about 4 degrees) compared with the Goss and S orientations (about 7-8 degrees)

Orientation-dependent recovery in strongly deformed Al-0.1% Mn crystals

Single crystals of Al-0.1% Mn were channel-die compressed to a true strain of 2.3 and their recovery behaviour at 240-320°C investigated by microhardness measurements, electron backscatter diffraction (EBSD) microtexture mapping and X-ray line broadening analysis. The crystal orientations were the nominally stable Goss {110}(001), brass {110}(112) and S {123}(634). For all three orientations the microhardness decreases with a logarithmic time dependence but the instantaneous recovery rates of the brass oriented crystals are systematically lower than those of the other two orientations by a factor of about 2. The dislocation densities decrease rapidly in the first stages of recovery (&lt;1 min) by dislocation dipole annihilation and more slowly thereafter. In the Goss and S orientations the later stage of recovery is due to sub-grain growth. The orientation dependence is ascribed to the relatively low misorientations developed by plastic straining in the brass crystals (average about 4°) compared with the Goss and S orientations (about 7-8°). © 2011 Taylor &amp; Francis