Combination of surface nanocrystallization and co-rolling: creating multilayer nanocrystalline composites

International audienceThis paper presents a combination of the surface mechanical attrition treatment (SMAT) and the corolling process performed at 550 °C. This duplex method leads to the formation of a semi-massive multilayer structure of alternating nanocrystalline layers, transition layers and coarse grain layers. Transmission electron microscope observations correlated with nanoindentation hardness measurements demonstrated that grain size in the nano- and sub-nanocrystalline layers is preserved after the process. Tensile tests showed improved yield and ultimate strengths, and acceptable ductility

High Strength Nanocrystallized Multilayered Structure Obtained by Smat and Co-rolling

International audienceIn the present study, a method is presented combining surface nanocrystalline treatment (SMAT) and the co-rolling process. The aim of this duplex treatment is the development of a 316L stainless steel semi-massive multilayered bulk structure with improved yield and ultimate tensile strengths, while conserving an acceptable elongation to failure by optimizing the volume fraction and distribution of the nano-grains in the laminate. To characterize this composite structure, tensile tests as well as sharp nanoindentation tests were carried out to follow the local hardness evolution through the cross-section of the laminate. Furthermore, transmission electron microscope (TEM) observations were carried out to determine the correlation between the microstructure, the local hardness and the mechanical response of the structure

Effect of interfacial oxidation occurring during the duplex process combining surface nanocrystallisation and co-rolling

International audienceThis paper presents an investigation of the interface quality of nanocristallised 316L stainless steel multilayer structures. They were produced by a duplex process, combining the Surface Mechanical Attrition Treatment (SMAT) and the co-rolling process at two different annealing temperatures (550°C and 650°C). Oxide layers were observed at the interfaces between the sheets and their morphology was characterised by optical microscopy. Their chemical composition was determined by Energy Dispersive X-ray spectrometry. The microstructure near the interfaces was analysed by Transmission Electron Microscopy (TEM). In the laminate co-rolled at 550°C, the presence of ultrafine grains was demonstrated. Additional tensile tests have shown an influence of the annealing temperature on the yield strength, as well as on the resistance of the interfaces of the co-rolled multilayer structures

Characterization of mechanical behavior of nanocrystalline layer induced by SMAT using micro-pillar compression technique coupled with finite element analysis

Micro-pillar compression tests were used to study the mechanical behavior of a stainless steel that has undergone SMAT (Surface Mechanical Attrition Treatment). Micro-pillars were machined using a Focused Ion Beam (FIB) on the cross-section of a SMATed specimen at different distances from the treated surface. These micro-pillars were thus located in different areas more or less affected by the SMAT. They were then compressed with a flat head mounted on a nanoindenter to obtain loading-displacement curves. These compression tests can give information on the mechanical gradient present from the top surface down to the bulk material after SMAT: a superficial nanocrystalline layer (from 10 to 50 micrometers thick and composed of grains with a diameter ranging from 10 to 50 nm) is indeed generated as well as a transition layer (between 200 and 300 micrometers thick and characterized by a grain size gradient from the nanometer to the micrometer scale as the distance from the surface increases) just below the nanocrystalline layer. These compression tests coupled with finite element analysis (FEA) can provide precious information at the mesoscopic scale on the mechanical behavior of the different layers present in the SMATed steel. FEA was used to study the effect of experimental parameters including taper angle (the angle between the tangent of wall and the axis of pillar), aspect ratio (the ratio of height and diameter of the pillar), and misalignment between the pillar axis and the compression direction. Based on the results of FEA, the constitutive behavior in the form of stress-strain curve was identified for the different layers beneath the treated surface including the nanocrystalline layer. According to the obtained stress-strain curves, the mechanical strength of the stainless steel is significantly improved after SMAT

Intergranular creep crack monitoring in 316H using Digital Image Correlation

International audienceAt elevated temperature (550°C) intergranular creep cracks have been observed in thermally and environmentally aged 316H stainless steel. To improve the understanding of mechanisms responsible of creep cracking, micromechanical experiments are proposed. An identification procedure of the crack tip position based on kinematic measurements is presented. Finite element simulations of intergranular cracks in bycristals have been performed and used as test fields to deform experimental images and to validate the image processing used for the identification

Imaging of 316H SENT creep sample subjected to oxidation at high temperature

International audienc

Comportement mécanique d'une structure multicouches obtenue par co-laminage de tôles nanostructurées par smat

Le but de cette étude consiste au développement de structures multicouches à hautes caractéristiques mécaniques obtenues par co-laminage de tôles en acier inoxydable 316L préalablement nanostructurées à travers le procédé SMAT (Surface Mechanical Attrition Treatment), puis à la modélisation par éléments finis de ces structures composites. Afin de quantifier l'influence de certains paramètres expérimentaux et d'évaluer la réponse mécanique des structures nanostructurées et co-laminées, un certain nombre d'essais ont été menés. Des mesures de dureté Vickers et de rugosité nous ont permis de caractériser la surface des matériaux traités. De plus, pour pouvoir suivre l'évolution de la microdureté des échantillons et pour pouvoir évaluer la taille de grains, des essais de nanoindentation ont été réalisés sur une section transverse des échantillons. Des essais de traction combinés aux mesures de dureté et microdureté ont permis de remonter aux caractéristiques mécaniques des différentes sous-couches et ainsi de simuler le comportement de la structure multicouche obtenue

DNA Methylation

<p><b>A</b>. X Chromosome DNA Methylation and XIST Expression. Methylation levels of genes in the X-chromosome (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118307#pone.0118307.s009" target="_blank">S6A Table</a>) are shown on the heatmap. Hierarchical clustering was performed on the samples, as indicated by the dendrogram. The genes are ordered according to their location (from the beginning to the end of the chromosome). Samples that show loss of DNA methylation for the “Enz” cluster are highlighted in blue, those that show DNA methylation for the “Ecm” cluster are highlighted in pink, and for both clusters in mauve. Genes located in the regions of loss of DNA methylation are listed to the right of the heatmap. XIST expression is shown on the line graph, with the detection limit for the microarray indicated by the red line. <b>B</b>. DNA methylation at imprinted loci. Methylation levels for imprinted probes (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118307#pone.0118307.s009" target="_blank">S6B Table</a>) are shown on the heatmap. Hierarchical clustering was performed on the samples, as indicated by the dendrogram. The genes are ordered according to chromosome location; genes are listed to the left. The inset at the right shows a detail of the NESP/GNAS complex locus, indicating the positions of the CpG sites that were hypermethylated (red triangle) vs. hypomethylated (green triangle) in the late passage samples relative to the NESP/GNAS and NESPAS exons. <b>C, D, E</b>. Heatmaps showing differential DNA methylation genes for early vs. late passage <b>(C)</b>, mechanical vs. enzymatic passage <b>(D)</b>, and Mef vs. Ecm substrate <b>(E)</b>. In heatmap <b>(C)</b>, the black boxes indicate genes for which the DNA methylation levels in the late passage MefMech (P103) samples was more similar to those in the early passage samples. Probes were selected by multivariate regression. Functional enrichments identified by GREAT analysis are shown to the right of the heatmaps, visualized using REVIGO [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118307#pone.0118307.ref013" target="_blank">13</a>]. Samples were arranged according to passage and culture method, and hierarchical clustering was performed on the genes only. In the functional enrichment results, the size of the node indicated the number of contributing GO terms, and color of the nodes indicates the FDR (darker color for lower FDR), and the edge length indicates the similarity between GO terms (shorter edge for more similar terms).</p

Replication of alpha-satellite DNA arrays in endogenous human centromeric regions and in human artificial chromosome

In human chromosomes, centromeric regions comprise megabase-size arrays of 171 bp alpha-satellite DNA monomers. The large distances spanned by these arrays preclude their replication from external sites and imply that the repetitive monomers contain replication origins. However, replication within these arrays has not previously been profiled and the role of alpha-satellite DNA in initiation of DNA replication has not yet been demonstrated. Here, replication of alpha-satellite DNA in endogenous human centromeric regions and in de novo formed Human Artificial Chromosome (HAC) was analyzed. We showed that alpha-satellite monomers could function as origins of DNA replication and that replication of alphoid arrays organized into centrochromatin occurred earlier than those organized into heterochromatin. The distribution of inter-origin distances within centromeric alphoid arrays was comparable to the distribution of inter-origin distances on randomly selected non-centromeric chromosomal regions. Depletion of CENP-B, a kinetochore protein that binds directly to a 17 bp CENP-B box motif common to alpha-satellite DNA, resulted in enrichment of alpha-satellite sequences for proteins of the ORC complex, suggesting that CENP-B may have a role in regulating the replication of centromeric regions. Mapping of replication initiation sites in the HAC revealed that replication preferentially initiated in transcriptionally active regions

Comportement mécanique de structures multicouches obtenues par co-laminage de tôles nanostructurées (essais et simulation)

De nombreuses études ont montré que les matériaux métalliques à grains nanométriques présentent des propriétés physiques, mécaniques et chimiques très souvent supérieures à celles de leurs homologues à taille de grains miscroscopique. Différentes technologiques de nanostructuration exploisant des principes physiques bien distincts ont vu le jour. Dans le cadre de cette thèse, la technique de nanocristallisation superficielle SMAT a été employée pour la génération d'une couche nanocristalline sur un acier inoxydable X2CrNiMo17-12-2 ainsi que sur un cuivre pur. Il a été montré que ce procédé permet d'atteindre un niveau de raffinement microstructural exceptionnel dans les couches superficielles des matériaux étudiés, et que ce dernier a pour effet une améioration de la tenue mécanique des matériaux SMATés. Un nouveau procédé a été proposé permettant d'augmenter la fraciton volumique des nanograins au sein du matériau, et ainsi améliorer sa tenue mécanique. Ce procédé, qualifié de procédé duplex, s'appuie à la fois sur le SMAT pour la nanocristallisation des matériaux, et sur le procédé de co-laminage pour générer une jonction entre les différentes tôles d'un empilement. ainsi, des structures multicouches à haut niveau de nanocristallisation et à haute résistance mécanique sont obtenues. Ces tructures multicouches ont été caractérisées à travers divers essais mécaniques et une étude microstructurale fine. Un modèle éléments finis d'un acier inoxydable SMATé a également été développéMany studies have shown that metallic materials with a grain size in the nanometer range exhibit enhanced physical, mechanical and chemical properties in comparison with their coarse grained counterparts. Several nanocristallisation techniques exploiting different physical principles have emerged. In this thesis, the surface nanocrystallisation technique SMAT has been used for the generation of nanocrystalline layers in 316L stainless steel and in pure copper. It has been shown that the SMA-Treatment achieves an unusual grain refinement in the surface layers of the treated materials, and leads to a considrable improvement of their mechanical behaviour. A new method has been proposed to increase the volume fraction of nanograins within the material, thus improving its mechanical strength. This so-called duplex process is a combination of the SMAT for the nanocrystallisation of the materials and the co-rolling process to produce a junction between the different sheets of a stack of MATed sheets. Thus, multilayer structures with increased volume fraction of nanograins and high mechanical strength are obtained. the corolled samples have been characterised through various mechanical tests and a careful microstructural study. A finite element model of a SMATed stainless steel has also been developedTROYES-SCD-UTT (103872102) / SudocSudocFranceF