CNRS Materials Science and Engineering

Grenoble, France

CNRS Materials Science and Engineering

Grenoble, France
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Pasturel A.,CNRS Materials Science and Engineering | Jakse N.,CNRS Materials Science and Engineering
Applied Physics Letters | Year: 2016

We investigate the conditions for the validity of the Stokes-Einstein relation that connects diffusivity to viscosity in melts using entropy-scaling relationships developed by Rosenfeld. Employing ab initio molecular dynamics simulations to determine transport and structural properties of liquid Al1-xCux alloys (with composition x ≤ 0.4), we first show that reduced self-diffusion coefficients and viscosities, according to Rosenfeld's formulation, scale with the two-body approximation of the excess entropy except the reduced viscosity for x = 0.4. Then, we use our findings to evidence that the Stokes-Einstein relation using effective atomic radii is not valid in these alloys while its validity can be related to the temperature dependence of the partial pair-excess entropies of both components. Finally, we derive a relation between the ratio of the self-diffusivities of the components and the ratio of their pair excess entropies. © 2016 Author(s).


Barlat F.,Pohang University of Science and Technology | Barlat F.,University of Aveiro | Gracio J.J.,University of Aveiro | Lee M.-G.,Pohang University of Science and Technology | And 2 more authors.
International Journal of Plasticity | Year: 2011

In this work, an approach is proposed for the description of the plastic behavior of materials subjected to multiple or continuous strain path changes. In particular, although it is not formulated with a kinematic hardening rule, it provides a reasonable description of the Bauschinger effect when loading is reversed. This description of anisotropic hardening is based on homogeneous yield functions/plastic potentials combining a stable, isotropic hardening-type, component and a fluctuating component. The latter captures, in average, the effect of dislocation interactions during strain path changes. For monotonic loading, this approach is identical to isotropic hardening, with an expanding isotropic or anisotropic yield surface around the active stress state. The capability of this constitutive description is illustrated with applications on a number of materials, namely, low carbon, dual phase and ferritic stainless steel samples.© 2011 Elsevier Ltd. All rights reserved.


Barlat F.,Pohang University of Science and Technology | Barlat F.,University of Aveiro | Ha J.,Pohang University of Science and Technology | Gracio J.J.,University of Aveiro | And 3 more authors.
International Journal of Plasticity | Year: 2013

The homogeneous anisotropic hardening (HAH) approach, which captures the Bauschinger effect in metallic materials effectively during load reversal, was extended to cross-loading cases with latent hardening effects. This continuum approach is based on the physical understanding of dislocation structure evolution during strain path changes but does not include the concept of kinematic hardening. The model was well validated for a deep drawing quality sheet sample. However, for a dual-phase steel, differences between predicted and experimental results were observed and discussed. Based on these results, additional validation tests and further improvement in the approach were suggested. © 2012 Elsevier Ltd.All rights reserved.


Colinet C.,CNRS Materials Science and Engineering | Tedenac J.-C.,Charles Gerhardt Institute
Intermetallics | Year: 2010

The point defect formation energies in D88-Sn3Ti5 are obtained from first principles calculations. The D88 structure is hexagonal, hP16, P63/mcm, prototype Mn5Si3. Four sublattices are introduced to account for the D88 structure and for the possibility of inserting atoms in the 2b sites of the structure P63/mcm. The 2b sites are not occupied in the stoichiometric compound at T = 0 K. But the possibility exists that a few atoms occupy these sites at high temperature or for off-stoichiometric alloys. A statistical model based on a mean-field approximation is developed in the canonical ensemble. The defect concentrations are calculated as function of temperature and deviation from stoichiometry. For stoichiometric D88-Sn3Ti5 alloys, the dominant thermal defects are composed of Sn atoms in interstitial positions 2b of the D88 structure and Ti atoms in antisite position on the sites preferentially occupied by Sn atoms. In the Sn-rich D88-Sn3Ti5, the constitutional defects are Sn atoms in interstitial positions. In the Ti-rich D88-Sn3Ti5, the constitutional defects are Ti atoms in antisite position. The chemical potentials as well as the Gibbs energy are obtained as function of composition for various temperatures. The extension of the one-phase domain of D88-Sn3Ti5 in the Sn-Ti phase diagram is calculated. © 2009 Elsevier Ltd. All rights reserved.


Colinet C.,CNRS Materials Science and Engineering | Tedenac J.-C.,Charles Gerhardt Institute
Intermetallics | Year: 2010

The total energies of intermetallic compounds in the Si-Ti system are calculated employing electronic density functional theory (DFT). The calculations are performed for the experimentally observed compounds and selected structures at their ideal stoichiometry. The calculated formation enthalpies are in good agreement with the available experimental data. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. The point defect formation energies in D88-Si3Ti5 (hP16, P63/mcm, prototype Mn5Si3) are obtained from first principles calculations. Four sublattices are introduced to account for the D88 structure and for the possibility of inserting atoms (2b Wyckoff positions of P63/mcm space group). The total energies of supercells containing one defect are calculated. A statistical model based on a mean-field approximation is used to obtain the defect concentrations, the chemical potentials and the Gibbs energy of formation as functions of temperature and deviation from stoichiometry. Analytical expressions of the defect concentrations, chemical potentials and Gibbs energy as functions of composition for various temperatures are provided. The off-stoichiometric domain of D88-Si3Ti5 is discussed. © 2010 Elsevier Ltd. All rights reserved.


Jakse N.,CNRS Materials Science and Engineering | Pasturel A.,CNRS Materials Science and Engineering
Journal of Physics Condensed Matter | Year: 2013

First-principles molecular dynamics simulations of liquid and undercooled aluminum have been performed to study the evolution of dynamic properties across the melting point. Single-atom as well collective dynamic properties are determined and are related to the structural evolution of the liquid phase. The temperature dependence of the self-diffusion coefficient is computed from both the mean square displacement and the velocity autocorrelation function. Self-diffusion coefficients follow an Arrhenius law with the single activation energy of 250 meV, consistent with experimental results for the liquid phase. Moreover, we show that the Arrhenius relation can also be applied to the undercooled state at T = 875 K. Finally, a direct calculation of the shear viscosity from the transverse current correlation function shows that the Stokes-Einstein relation can be applied over the temperature range investigated. © 2013 IOP Publishing Ltd.


Rethore J.,INSA Lyon | Estevez R.,CNRS Materials Science and Engineering
Journal of the Mechanics and Physics of Solids | Year: 2013

We present a new methodology for the identification of a zone cohesive model that describes material failure. The material under consideration fails by crazing. The study is conducted at the micron scale in order to capture and analyze the fracture mechanism. The crack tip displacement fields are measured optically by Digital Image Correlation. The local stress intensity factors (mode I and II) and the location of the equivalent elastic crack tip are calculated during the loading. The variation of the location of the equivalent crack tip is used to track the initiation and growth of the process zone, up to the onset of crack propagation. These experimental measurements are used to define the appropriate parameters in a cohesive zone model. The methodology addresses the onset of crazing, the traction-separation profile and the maximum opening corresponding to the local nucleation of a crack. The cohesive parameters that are derived from the experimental data are consistent with results available in the literature. In addition, the model enables the characterization of the normal and tangential mode of the cohesive model. © 2013 Elsevier Ltd.


Lepinoux J.,CNRS Materials Science and Engineering
Philosophical Magazine | Year: 2010

Kinetic Monte Carlo simulations of precipitation in AlZr alloys are compared with predictions of cluster dynamics based on an enhanced thermodynamic model. A methodology and various tools are proposed to learn as much as possible from such comparisons. Important deviations between the two methods are investigated and interpreted through the role of different mechanisms. © 2010 Taylor & Francis.


Vermaak N.,CNRS Materials Science and Engineering | Parry G.,CNRS Materials Science and Engineering | Estevez R.,CNRS Materials Science and Engineering | Brechet Y.,CNRS Materials Science and Engineering
Acta Materialia | Year: 2013

Zirconium alloys are typically used in nuclear pressurized water reactors (PWR) as fuel cladding tubes due to their chemical stability and their mechanical strength at operating temperatures (≈300 C). However, the corrosion of Zr-based cladding tubes is one of the factors limiting the burn-off rate in PWRs. It is commonly accepted that the corrosion kinetics involves a periodic succession of growth where the oxide thickness varies parabolically with time. As the oxide thickens, a cracking structure forms. The oxide appears striated with periodic layers of cracks running parallel to the metal/oxide interface. This cracking structure has been experimentally related to the periodicity of the oxide growth. In the present work, a finite-element study is used to investigate the development of stresses in the oxide under the combined influence of molar volume expansion during oxide formation, metal/oxide interface geometry and metallic substrate creep. The generation of tensile stresses capable of initiating the cracks that are observed experimentally is explored. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Barrat J.-L.,Joseph Fourier University | Rodney D.,CNRS Materials Science and Engineering
Journal of Statistical Physics | Year: 2011

Recently, Dammak and coworkers (Phys. Rev. Lett. 103:190601, 2009) proposed that the quantum statistics of vibrations in condensed systems at low temperature could be simulated by running molecular dynamics simulations in the presence of a colored noise with an appropriate power spectral density. In the present contribution, we show how this method can be implemented in a flexible manner and at a low computational cost by synthesizing the corresponding noise 'on the fly'. The proposed algorithm is tested for a simple harmonic chain as well as for a more realistic model of aluminium crystal. The energy and Debye-Waller factor are shown to be in good agreement with those obtained from harmonic approximations based on the phonon spectrum of the systems. The limitations of the method associated with anharmonic effects are also briefly discussed. Some perspectives for disordered materials and heat transfer are considered. © 2011 Springer Science+Business Media, LLC.

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