14 research outputs found
RELATION BETWEEN HARDNESS OF (Ti, Al)N BASED MULTILAYERED COATINGS AND PERIODS OF THEIR STACKING
This study aims to model, by using a finite element method, the relationship between the hardness and the period Î of metal/nitride multilayer coatings (Ti0.54Al0.46/Ti0.54Al0.46N)n in order to understand the increase of the hardness at the low periods [1] and then optimise the multilayer coating architecture to obtain the best mechanical properties. A 2D axisymmetric finite element model of the Berkovich nanoindentation test was developed. The coating was designed as a stacking of Ti0.54Al0.46 and Ti0.54Al0.46N nanolayers with, in the first hypothesis, equal thickness and perfect interface. The elastoplastic behaviours of the metal and nitride layers were identified by Berkovich nanoindentation experiments and inverse analysis on thick monolayer samples. The indentation curves (P-h) obtained by this model depend on the period Î of the stacking. Simulated (P-h) curves were compared with experimental data on 2 ÎŒm thick films with different periods Î ranging from 10 to 50 nm deposited by RF magnetron sputtering using reactive gas pulsing process (RGPP). The model forecasts are very consistent with the experience for the largest period but the model does not reproduce the hardness increase at the lowest periods. The Î = 10 nm coating was analysed by electron energy loss spectroscopy (EELS) on a transmission electron microscope. Results show intermixing of the layers with the presence of nitrogen atoms in the metal layer over a few nanometers [1]. It was concluded that the metal/ceramic interface plays an important role at low periods. The addition in the model of a transition layer in the metal/nitride stacking, with an elastoplastic metal/ceramic medium behaviour, allows to reproduce the nanoindentation experimental curves. The thickness of this transition layer deduced from model updating method is in very good agreement with EELS observations
Strain localization and anisotropic correlations in a mesoscopic model of amorphous plasticity
A mesoscopic model for shear plasticity of amorphous materials in two
dimensions is introduced, and studied through numerical simulations in order to
elucidate the macroscopic (large scale) mechanical behavior. Plastic
deformation is assumed to occur through a series of local reorganizations.
Using a discretization of the mechanical fields on a discrete lattice, local
reorganizations are modeled as local slip events. Local yield stresses are
randomly distributed in space and invariant in time. Each plastic slip event
induces a long-ranged elastic stress redistribution. Rate and thermal effects
are not discussed in the present study. Extremal dynamics allows for recovering
many of the complex features of amorphous plasticity observed experimentally
and in numerical atomistic simulations in the quasi-static regime. In
particular, a quantitative picture of localization, and of the anisotropic
strain correlation both in the initial transient regime, and in the steady
state are provided. In addition, the preparation of the amorphous sample is
shown to have a crucial effect of on the localization behavior
Relation between hardness of multilayered (Ti,Al)N based coatings and periods of their stacking
International audienceThis study aims to model, by using a finite element method, the relationship between the hardness and the period Î of metal/nitride multilayer coatings (Ti0.54Al0.46/Ti0.54Al0.46N)n in order to understand the increase of the hardness at the low periods [1] and then optimise the multilayer coating architecture to obtain the best mechanical properties. A 2D axisymmetric finite element model of the Berkovich nanoindentation test was developed. The coating was designed as a stacking of Ti0.54Al0.46 and Ti0.54Al0.46N nanolayers with, in the first hypothesis, equal thickness and perfect interface. The elastoplastic behaviours of the metal and nitride layers were identified by Berkovich nanoindentation experiments and inverse analysis on thick monolayer samples. The indentation curves (P-h) obtained by this model depend on the period Î of the stacking. Simulated (P-h) curves were compared with experimental data on 2 ÎŒm thick films with different periods Î ranging from 10 to 50 nm deposited by RF magnetron sputtering using reactive gas pulsing process (RGPP). The model forecasts are very consistent with the experience for the largest period but the model does not reproduce the hardness increase at the lowest periods. The Î = 10 nm coating was analysed by electron energy loss spectroscopy (EELS) on a transmission electron microscope. Results show intermixion of the layers with the presence of nitrogen atoms in the metal layer over a few nanometers [1]. It was concluded that the metal/ceramic interface plays an important role at low periods. The addition in the model of a transition layer in the metal/nitride stacking, with an elastoplastic metal/ceramic medium behaviour, allows to reproduce the nanoindentation experimental curves. The thickness of this transition layer deduced from model updating method is in very good agreement with EELS observations
ModĂ©lisation du lien entre la duretĂ© et la pĂ©riode dâempilement dans un revĂȘtement mĂ©tal/cĂ©ramique nano-architecturĂ© en multicouche
International audienceLes nitrures mĂ©talliques de titane et dâaluminium (TiAl)N sont des revĂȘtements utilisĂ©s depuis de nombreuses annĂ©es pour leurs propriĂ©tĂ©s remarquables de duretĂ© et de rĂ©sistance Ă lâoxydation. Il a Ă©tĂ© montrĂ© que le module dâindentation et la duretĂ© de revĂȘtements Ti(1-x)AlxN dĂ©pendent de la teneur en aluminium et que les propriĂ©tĂ©s optimales sont obtenues pour x=0,46 [1,2]. Une possibilitĂ© dâamĂ©lioration de la duretĂ© de ce type de revĂȘtement est de les architecturer en multicouche mĂ©tal/cĂ©ramique. Lâobjectif est de modĂ©liser le lien entre la duretĂ© dâun revĂȘtement [Ti0,54Al0,46/Ti0,54Al0,46N]n et la pĂ©riode Î de lâempilement des couches afin de comprendre les phĂ©nomĂšnes qui gĂ©nĂšrent lâaugmentation de la duretĂ© aux plus faibles pĂ©riodes [3]. Un modĂšle numĂ©rique de lâessai de nanoindentation Berkovich sur des Ă©chantillons nanostratifiĂ©s a Ă©tĂ© Ă©laborĂ©. Lâinterface mĂ©tal/cĂ©ramique est considĂ©rĂ©e parfaite et sans Ă©paisseur. Les comportementsĂ©lastoplastiques des couches Ă©lĂ©mentaires de mĂ©tal et de cĂ©ramique ont Ă©tĂ© identifiĂ©s par nanoindentation Berkovich sur des Ă©chantillons revĂȘtus dâune seule couche. Ce modĂšle Ă©lĂ©ments finis 2D axisymĂ©trique permet dâobtenir la courbe dâindentation (P-h) pour des nanostratifiĂ©s en fonction de la pĂ©riode Î et dâune vingtaine dâautres paramĂštres (Ă©lastoplastiques, gĂ©omĂ©triques, dimensionnels, âŠ). Afin de confronter ce modĂšle Ă des expĂ©riences, des nanostratifiĂ©s dâĂ©paisseur dâenviron 2 micromĂštres de diffĂ©rentes pĂ©riodes Î (de 10 Ă 50 nm) ont Ă©tĂ© architecturĂ©s par pulvĂ©risation rĂ©active Ă signal de commande cyclique (RGPP) en alternant une couche Ti0,54Al0,46 et une couche Ti0,54Al0,46N. Les Ă©chantillons ainsi obtenus ont Ă©tĂ© testĂ©s par nanoindentation Berkovich. Les prĂ©visions du modĂšle sont en trĂšs bon accord avec lâexpĂ©rience pour la plus grande pĂ©riode (50 nm), mais se dĂ©gradent lorsque la pĂ©riode diminue. Le modĂšle ne permet pas de reproduire lâaugmentation de la duretĂ© aux plus faibles pĂ©riodes. Une analyse de sensibilitĂ© du modĂšle de la courbe dâindentation a Ă©tĂ© menĂ©e. Elle montre lâimportance de la fraction volumique de cĂ©ramique dans le systĂšme bicouche mĂ©tal/cĂ©ramique et de lâĂ©crouissage de la couche mĂ©tallique. Une analyse spectrographique par spectroscopie de perte d'Ă©nergie des Ă©lectrons au microscope Ă©lectronique Ă transmission pour la pĂ©riode Î=10 nm a mis en Ă©vidence une proportion dâazote dans la couche mĂ©tallique sur quelques nanomĂštres, signe dâune intermixion des couches. Ces rĂ©sultats montrent que des phĂ©nomĂšnes Ă©lastoplastiques Ă lâinterface mĂ©tal/cĂ©ramique jouent un rĂŽle important aux faibles pĂ©riodes et remettent en cause lâhypothĂšse initiale dâinterface parfaite et sans Ă©paisseur. Il est montrĂ© que lâajout dans le modĂšle dâune couche de transition ayant un comportement Ă©lastoplastique moyen mĂ©tal/cĂ©ramique permet de reproduire les courbes de nanoindentation expĂ©rimentales et que lâĂ©paisseur de cette couche est en trĂšs bon accord avec les observations spectroscopiques
ModĂ©lisation du lien entre la duretĂ© et la pĂ©riode dâempilement dans un revĂȘtement mĂ©tal/cĂ©ramique nano-architecturĂ© en multicouche
International audienceLes nitrures mĂ©talliques de titane et dâaluminium (TiAl)N sont des revĂȘtements utilisĂ©s depuis de nombreuses annĂ©es pour leurs propriĂ©tĂ©s remarquables de duretĂ© et de rĂ©sistance Ă lâoxydation. Il a Ă©tĂ© montrĂ© que le module dâindentation et la duretĂ© de revĂȘtements Ti(1-x)AlxN dĂ©pendent de la teneur en aluminium et que les propriĂ©tĂ©s optimales sont obtenues pour x=0,46 [1,2]. Une possibilitĂ© dâamĂ©lioration de la duretĂ© de ce type de revĂȘtement est de les architecturer en multicouche mĂ©tal/cĂ©ramique. Lâobjectif est de modĂ©liser le lien entre la duretĂ© dâun revĂȘtement [Ti0,54Al0,46/Ti0,54Al0,46N]n et la pĂ©riode Î de lâempilement des couches afin de comprendre les phĂ©nomĂšnes qui gĂ©nĂšrent lâaugmentation de la duretĂ© aux plus faibles pĂ©riodes [3]. Un modĂšle numĂ©rique de lâessai de nanoindentation Berkovich sur des Ă©chantillons nanostratifiĂ©s a Ă©tĂ© Ă©laborĂ©. Lâinterface mĂ©tal/cĂ©ramique est considĂ©rĂ©e parfaite et sans Ă©paisseur. Les comportementsĂ©lastoplastiques des couches Ă©lĂ©mentaires de mĂ©tal et de cĂ©ramique ont Ă©tĂ© identifiĂ©s par nanoindentation Berkovich sur des Ă©chantillons revĂȘtus dâune seule couche. Ce modĂšle Ă©lĂ©ments finis 2D axisymĂ©trique permet dâobtenir la courbe dâindentation (P-h) pour des nanostratifiĂ©s en fonction de la pĂ©riode Î et dâune vingtaine dâautres paramĂštres (Ă©lastoplastiques, gĂ©omĂ©triques, dimensionnels, âŠ). Afin de confronter ce modĂšle Ă des expĂ©riences, des nanostratifiĂ©s dâĂ©paisseur dâenviron 2 micromĂštres de diffĂ©rentes pĂ©riodes Î (de 10 Ă 50 nm) ont Ă©tĂ© architecturĂ©s par pulvĂ©risation rĂ©active Ă signal de commande cyclique (RGPP) en alternant une couche Ti0,54Al0,46 et une couche Ti0,54Al0,46N. Les Ă©chantillons ainsi obtenus ont Ă©tĂ© testĂ©s par nanoindentation Berkovich. Les prĂ©visions du modĂšle sont en trĂšs bon accord avec lâexpĂ©rience pour la plus grande pĂ©riode (50 nm), mais se dĂ©gradent lorsque la pĂ©riode diminue. Le modĂšle ne permet pas de reproduire lâaugmentation de la duretĂ© aux plus faibles pĂ©riodes. Une analyse de sensibilitĂ© du modĂšle de la courbe dâindentation a Ă©tĂ© menĂ©e. Elle montre lâimportance de la fraction volumique de cĂ©ramique dans le systĂšme bicouche mĂ©tal/cĂ©ramique et de lâĂ©crouissage de la couche mĂ©tallique. Une analyse spectrographique par spectroscopie de perte d'Ă©nergie des Ă©lectrons au microscope Ă©lectronique Ă transmission pour la pĂ©riode Î=10 nm a mis en Ă©vidence une proportion dâazote dans la couche mĂ©tallique sur quelques nanomĂštres, signe dâune intermixion des couches. Ces rĂ©sultats montrent que des phĂ©nomĂšnes Ă©lastoplastiques Ă lâinterface mĂ©tal/cĂ©ramique jouent un rĂŽle important aux faibles pĂ©riodes et remettent en cause lâhypothĂšse initiale dâinterface parfaite et sans Ă©paisseur. Il est montrĂ© que lâajout dans le modĂšle dâune couche de transition ayant un comportement Ă©lastoplastique moyen mĂ©tal/cĂ©ramique permet de reproduire les courbes de nanoindentation expĂ©rimentales et que lâĂ©paisseur de cette couche est en trĂšs bon accord avec les observations spectroscopiques
Breast-Associated Adipocytes Secretome Induce Fatty Acid Uptake and Invasiveness in Breast Cancer Cells via CD36 Independently of Body Mass Index, Menopausal Status and Mammary Density
International audienceBreast adiposity is correlated with body mass index, menopausal status and mammary density. We here wish to establish how these factors influence the cross-talk between breast adipocytes and normal or malignant breast cells. Adipocyte-derived stem cells (ASCs) were obtained from healthy women and classified into six distinct groups based on body mass index, menopausal status and mammary density. The ASCs were induced to differentiate, and the influence of their conditioned media (ACM) was determined. Unexpectedly, there were no detectable differences in adipogenic differentiation and secretion between the six ASC groups, while their corresponding ACMs had no detectable influence on normal breast cells. In clear contrast, all ACMs profoundly influenced the proliferation, migration and invasiveness of malignant breast cells and increased the number of lipid droplets in their cytoplasm via increased expression of the fatty acid receptor CD36, thereby increasing fatty acid uptake. Importantly, inhibition of CD36 reduced lipid droplet accumulation and attenuated the migration and invasion of the breast cancer cells. These findings suggest that breast-associated adipocytes potentiate the invasiveness of breast cancer cells which, at least in part, is mediated by metabolic reprogramming via CD36-mediated fatty acid uptake