CoMet : Behavior and Microstructure of Metals

last update: nov 15th, 2012

Heads: Olivier Castelnau (Senior Researcher), and Zehoua Hamouche (Assoc. Prof.)

Staff: Sarah Baiz (Engineer), Chedly Braham (Assoc. Prof.), Jean-Pierre Chevalier (Prof.), Katell Derrien (Assoc. Prof.), Justin Dirrenberger (Assoc. Prof.), Sébastien Dubent (Engineer),  Véronique Favier (Prof.), Imade Koutiri, Nicolas Ranc (Assoc. Prof.), Frédéric Vales (Engineer - Microscopies), Olivier Zanellato (Assoc. Prof.)

PhD: Alexandre Gaultier,Tang Gu, Paul Lafourcade, Jean-Baptiste Marijon,  Khalil Traidi, Noushin Torabian, Shaobo Yang, Biagio Zaffora

Other: Vincent Michel (IE – Rayons X), Taylan ORS (Post-doc), Idriss TIBA (ATER)


The aim of this research group is the understanding of the thermomechanical behavior of metallic materials (and more generally of polycrystalline materials) by making use of experimental, theoretical, and numerical micromechanical approaches. The microstructure of investigated materials is specified by the random character of grain arrangement (morphologic and crystallographic textures), but it can also exhibit property gradients at different scales. Two research directions are developed simultaneously:

(i) Influence of processes on the evolution and transformation of microstructures. Emphasis is placed on laser processes (drilling, shock...) and the strong associated gradients, although microstructure evolutions occurring during more standard processes such as very high cycles fatigue are also investigated.

(ii) The effect of microstructures on the behavior is investigated in the general context of elasto-visco-plastic behaviors. Beyond the influence of crystallographic textures and strain hardening, specific microstructures (e.g. nanostructured thin films, columnar grains, multiphase materials, partially molten metals and minerals …) are investigated.

Studies that are carried out are systematically based on the description of scales transitions relevant for the problem of interest (dislocation structure, grains, polycrystal, macro-homogeneous sample, or structure piece). We take advantage of the experimental equipment and knowhow of the laboratory (X-Rays, Microscopies, Mechanical testing, Laser …) and specific developments are made when necessary. Strain, stress, and temperature field measurements, involving respectively image correlation, X-rays (lab/synchrotron) or neutrons diffraction, and pyrometry techniques, used at different scales (micrometer to centimeter), are receiving a special interest. The interpretation of these measurements relies on homogenization techniques allowing the understanding of the mechanical interactions occurring between constituents, and the impact of these interactions on the specimen behavior.

Actual funded projects

Microstructure and behavior of zirconia for glass melting (ANR ASZTECH)

Collaborations : Ecole des Mines (CdM, Evry), GEMH (Limoges), LEM3 (Metz), Saint Gobain CREE, et Mistras Group SA.

In this project (2013-2017), we are studying the internal stresses that develop in the large zirconia walls of glass oven, in relation with the elaboration process and with the microstructure of this composite. For this we will be using large scale facilities such as neutrons and synchrotron radiation.

Architectured and nanostructured Cu-Nb composites (ANR METAFORES)

Collaborations : Pprime (Poitiers), LLB (Saclay) , CdM (Evry), et LNCMI (Toulouse).

The METAFORES project (2012-2016) aims at investigating the behavior of architectured and nanostructured Cu-Nb composites used for the generation of intense magnetic fields. Our team is concerned with the micromechanical modeling of the mechanical and electrical properties, in relation with the material microstructure.

Architectured Cu-Nb composite. The smallest grains are nanometric.

Lower density and higher modulus steel composites (ANR ADRERA)

Collaborations: MATEIS (INSA Lyon), Arcelor Mittal, SIMAP (INP Grenoble), LPCES (ICMMO Orsay), LSPM (Villetaneuse), ICMPE (Paris Est) and LPS ( Paris-Sud Univ.).

The aim of this project is to develop a new steel matrix composite with lower density and improved stiffness. The chosen reinforcement is TiB2, a technical ceramic. The major novelty of this material is its elaboration route: while most other Fe-TiB2 composites are obtained by powder metallurgy, this material is manufactured by continuous casting, which allows for mass production and more standard shaping processes. Depending on the targeted components, their mass can be reduced by 20 to 30 % with the use of this material. This represents an interesting prospect for the automotive industry.

Researchers at CoMet are studying the mechanical behaviour and the development of damage in the composite in relation with the microstructure. The idea is to characterise the cohesion of the interface matrix / reinforcement during plastic deformation and deduce a damage criterion based on microstructure. This work is performed in close collaboration with ICMPE-CNRS, Thiais on the atomic structure of interfaces and LPS, Orsay on the composition of the interfaces.

 Damage in new titanium diboride (TiB2)- steel based composite
 

Rheology and anisotropies of Earth mantle minerals (ANR MANTLE RHEOLOGY)

Collaborations: UMET- Univ. Lille, ESRF-Grenoble.

This project aims at the development of a multiscale approach (from the dislocation structure to the centimetric scale) for the rheology of minerals (ex. olivine, pyroxenes), which plastic behavior is extremely anisotropic, deformed at high pressure (tens of GPa) and high temperature (1000-2000°C). Several models adapted to the different scales are compared to synchrotron experiments carried out on a new D-DIA apparatus installed at the ESRF. The characterization of pressure effects on mineral rheology opens important perspectives in Earth sciences, but more generally the project allows going deeper in the understanding of highly anisotropic materials. Our contribution is focussed on the application of mean-field homogenization methods for the estimation of the effective behavior of these minerals.

(left) Periodic microstructure of an olivine polycrystal and (right) intragranular distribution of equivalent stress (normalized) during a creep test.

Microplasticity and dissipation under fatigue in the giga-cycles range (ANR DISFAT)

Collaborations: LEME – Univ. Ouest Paris La défense, LMGC – Univ. Montpellier II, LPMTM – Univ. Paris Nord, CETIM – Senlis.

We are studying crack initiation in ductile materials when specimens are subjected to cyclic loading with stress amplitudes smaller than the conventional fatigue limit. Under these conditions, lifetime can exceed 109 cycles (Very High Cycle Fatigue). Special emphasis is placed on the detection of crack initiation, which is difficult owing to the small considered stress levels. Microstructural changes are investigated by (i) the specimen temperature change during loading cycles and the estimation of a dissipation field, (ii) surface roughness and roughness evolution (SEM and AFM), and (iii) dislocation structures (TEM).

Within the framework of this project, the PhD of Ngoc Lam Phung has been defended in dec. 2012. The PhD work of Nicolas Marti (2010-2013, collaboration with Nicolas Saintier from LAMEFIP, Arts et Métiers ParisTech at Bordeaux) is about the influence of frequency and temperature on deformation mechanisms and dissipation during fatigue tests at small stress amplitude.

    

(Left)Temperature field measurement device by thermography. (Right) Observation with SEM of persistant slip bands on the copper specimen surface after solicitation: Ngoc lam Phung thesis.

Laser drilling (ANR ULTRA)

Collaborations : Centre des Matériaux – Mines ParisTech, SNECMA, CRMA, Lasag, Laser Métrologie.

Laser drilling is of current use for aeronautic applications and particularly for the cooling of engines. However, actual processes do not allow the drilling of coated materials (heat barrier) with sufficient constraints on quality, reproducibility, and lifetime required by the development of future engines. With this project we are willing to reach significant advances on Laser drilling processes, both at the technical (realization of a new adaptative drilling head) and scientific (laser absorption, damages...) points of view. Investigated materials include superalloys (AM1, KCN22W) with or without coating. This project is a collaborative work between groups « properties and microstructure of metals », « Structure and Dynamic of Systems », and « Laser processes » of PIMM lab.

In the PhD of Jeremie Girardot (2010-2013), Laser drilling process is simulated in order to assess temperature gradients in the heat affected zone, the associated microstructure evolution, defects, and mechanical behavior, for low to middle Laser intensities (MW/cm2- GW/cm2). Applications concern the cooling chamber system in aircraft engines, for different materials : superalloys (cobalt base) and ceramic (layer of thermal barrier).

Optical micrograph after Laser drilling (material: KCN22W)

Stress field at the micron scale (ANR MICROSTRESS)

Collaborations: EDF R&D, UR Navier, LMS-X, CEA-Grenoble, LCG-Mines St-Etienne, CEA-Cadarache, LEME

This project aims at developping techniques for the measurement of the stress field in polycrystalline materials of industrial use, with a (sub)micrometric spatial resolution, i.e. to characterize intragranular stress heterogeneities. At PIMM, we are focussed on the Laue microsiffraction technique available at synchrotron ESRF (beamline BM32), and results will be compared with a high angular resolution EBSD technique developed at lab LCG in St Etienne. Important parts of the project comprise the optimisation of the experimental setup and of the treatment of Laue images, the estimation of a realistic uncertainty on results, and the application of the method to the case of a material (stainless steel 316L) of industrial use at small plastic strain.

M. Fengguo Zhang is doing a PhD (2011-2014, collaboration with M. Bornert, UR Navier, funded by the China Scholarship Council) aims at using Digital Image Correlation (DIC) techniques to interpret Laue microdiffraction images obtained under synchrotron radiation, in order to get maps of the stress field in deformed polycrystals, with s (sub)micrometric spatial resolution and (hopefully) a stress resolution of the order of a MPa.  Fengguo Zhang will provide an accurate estimation of measurement uncertainties, and will terminate his work with an application to an austenitic steel (316L) deformed in-situ at small plastic strain.

The PhD of Jean-Baptiste Marijon (2012-2015, collaboration with O. Robach, CEA-Saclay / ESRF) is focussed on the use of Laue microdiffraction for the 3D reconstruction of the near surface microstructure and in-depth stress gradient of polycrystalline material under in situ plastic deformation.

Emeric Plancher (2012-2015, collaboration with C. Maurice - Mines St Etienne, and L. Saintoyant - EDF) will focuss during his PhD on an application of High Resolution EBSD and Laue microdiffraction to 316L steel in order to provide maps of intergranular stress fluctuation with micrometric spatial resolution.

(left) Laue microdiffraction allows characterizing materials at the intragranular scale. (right) Laue image obtained at the ESRF beamline BM32 on a bulk tungsten specimen during in situ tensile test.

Direct laser elaboration of Ti-TiC composites

In his PhD (2012-2015), Sebastien Pouzet is investigating the microstructure and the associated mechanical behavior of Ti-TiC metal matrix composites elaborated by direct laser deposition. During this collaborative work with the laser group of our lab (Patrice Peyre), we expect achieving an optimisation of the laser elaboration process.

Microstructure of a Ti-TiC composite elaborated by direct laser deposition

Treatment and passivation of surfaces by laser processes

Collaborations : CEA-Saclay

The steam generator is one of the most important component of the primary circuit of  pressure-fed water nuclear reactors. It is constituted of 690 nickel base alloy which is used for its good corrosion resistance. A previous research work conducted at CEA demonstrated that surface treatment via laser remelting improved the corrosion resistance over time, while keeping good mechanical properties in the bulk material.

Lucille Gouton’s PhD (2012-2015) aims at investigating laser-material interaction on the specimen surface made of 690 nickel base alloy to produce a thin continuous layer of chromine and thus improving the surface passivity. Two laser surface treatments are studied:

  • Surface treatment via laser remelting
  • Layer deposition by laser surfacing.

This PhD is a collaboration with the Laser group at PIMM.

Behavior of a multiphase material

Collaborations : H. Sidhom,  ESSTT Tunis, Tunisie

Yahyaoui Houda is doing a PhD on the fatigue behavior of multiphase materials, putting together experimental and numerical approaches.

Analysis of stress gradients by XRD

Collaborations : A. Baczmanski, Univ. krakow, Poland

The thesis of Marcisko Marianna is focussed on the mechanical properties and residual stresses induced by surface transformation in polycrystalline materials, studied by X-ray diffraction (dir. Chedly Braham in collaboration w/  A. Baczmanski, univ. Krakow, Poland).

Previous PhDs and post-docs