J.-M. Drezet

École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

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Publications (73)72.77 Total impact

  • N. Chobaut · D. Carron · J.-M. Drezet
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    ABSTRACT: The precipitation of an AA2618 Al-Cu-Mg alloy is monitored during isothermal holdings and continuous coolings. The Time-Temperature-Property and Continuous-Cooling-Precipitation diagrams of AA2618 are obtained using in-situ resistivity and differential scanning calorimetry respectively. The two precipitation domains observed at high temperature and low temperature (<300 °C) are discussed with regard to their influence on the mechanical properties during quenching of large components.
    No preview · Article · Jan 2016 · Journal of Alloys and Compounds
  • J.-M. Drezet · N. Chobaut · T. Pirling
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    ABSTRACT: The direct chill casting of rectangular ingots gives rise to large thermally induced strains that lead to several types of casting defects (distortions, cold cracks and hot tearing) and downstream processing issues during sawing especially for high strength alloys and large formats. To reduce stresses, wipers are placed below the mould to eject the falling water from the ingot which gets hotter. As-cast stresses have been determined in AA7050 rectangular ingots cast with and without a wiper using neutron diffraction measurements and a 3D casting model. The stress level is reduced by 33% and the stored elastic energy by 50%.
    No preview · Article · Dec 2015
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    ABSTRACT: In this paper, a simple but realistic approach is presented to predict the as-quenched residual stress distribution in thick 7xxx aluminium alloy plates. Instead of modelling precipitation that occurs during quenching, a thermo-mechanical model is used whose parameters are identified using a limited number of tensile tests achieved after representative interrupted cooling paths in a Gleeble machine. The material behaviour law accounts for recovery at high temperature in a simple way and neglects the Bauschinger effect as suggested by a dedicated experiment. The results of this simple approach are compared to residual stress measurements in plates of different thicknesses for two different 7xxx alloys, AA7449 and AA7040.
    Full-text · Article · Aug 2015 · Journal of Materials Processing Technology
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    ABSTRACT: Early subnanometre cluster formation during quenching of a high-strength AA7449 aluminium alloy was investigated using in situ small angle X-ray scattering. Fast quench cooling was obtained by using a laser-based heating system. The size and number density of homogeneous nucleated clusters were found to be strongly dependent on the cooling rate, while the volume fraction of cluster formation is independent of the cooling rate. Heterogeneous larger precipitation starts at higher temperatures in volume fractions that depend on the cooling rate. (C) 2014 AIP Publishing LLC.
    Full-text · Article · Sep 2014 · Applied Physics Letters
  • J.-M. Drezet · Th. Pirling
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    ABSTRACT: As-cast stresses in the foot of the ingot corresponding to the transient start-up phase of the direct chill casting have been determined in aluminum alloy AA7050 rectangular ingots. This high strength alloy is usually cast with a wiper that is placed below the mold and ejects the falling water from its surface thus reducing the cooling intensity. The ingot being hotter, internal stresses are relaxed. The efficiency of a wiper has been evaluated using both neutron diffraction measurements on ingots cast with and without a wiper and a 3D numerical model simulating the stress generation during casting. The stress level is reduced by 33% when a wiper is used during casting and the stored elastic energy by 50%.
    No preview · Article · Jul 2014 · Journal of Materials Processing Technology
  • Nicolas Chobaut · Denis Carron · Jean Marie Drezet
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    ABSTRACT: A conventional way to determine precipitation kinetics in heat treatable aluminium alloys is to monitor the associated solute loss by in-situ resistivity. A Gleeble machine is used to perform so called isothermal quenching (IQ) resistivity measurements. IQ consists in quenching the alloy down to a given temperature and holding it at this temperature. The results are validated against measurements performed with a classical four-points method using continuous current on the same alloy.
    No preview · Article · Jun 2014 · Materials Science Forum
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    ABSTRACT: Zirconium is always present in Ni base superalloys as it enhances their creep properties. In the present study, the influence of very small Zr additions, 100–400 ppm, i.e. 0.01–0.04 wt.%, on hot tearing of IN738LC superalloy is experimentally investigated using dedicated turbine blade castings. Although the Zr content remains very small, it has a strong effect on hot tearing tendency. Microstructure of hot tear in as-cast samples reveal that grain size and secondary dendrite arm spacing have no significant effect on hot tearing. On the other hand eutectic phase volume fraction and its dispersion or spreading along grain boundaries drastically affect the hot tearing propensity and strongly increase with increasing amounts of Zr. Hence grain coalescence becomes impossible at grain boundaries covered with eutectic phase films. With increasing Zr content, gain coalescence between two distinct grains with no interdendritic phase requires more undercooling. Coalescence is retarded and occurs deeper in the mush zone, i.e. at lower temperatures resulting in a higher sensitivity to hot tearing. Finally, it is shown that a reduction of Zr content to 0.02 wt.% is required to fully suppress hot tearing in polycrystalline IN738LC blades.
    Preview · Article · Mar 2014 · Journal of Materials Processing Technology
  • J.-M. Drezet · P. Celle · O. Ribaud · Th. Pirling
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    ABSTRACT: During casting, thermally induced deformations give birth to ingot distortions and residual stresses. For some high strength alloys, ingot cracking can happen during casting per se or during cooling down. Ingot distortions such as rolling face pull-in, but curl and but swell are rather easy to quantify as opposed to internal stresses. As aluminium is rather transparent to neutrons, residual stress measurements using neutron diffraction appeared to be a good way to validate the thermomechanical models aimed at simulating the stress build-up during casting. This technique has been applied to DC cast AA7050 rolling plate ingots with special attention to the stress generation in the transient start-up phase, i.e. in the foot of the ingot. Additional results using the hole drilling method complement the measurements. The measured stress distributions are compared with the results of a numerical model of DC casting for ingots cast with and without a wiper.
    No preview · Article · Jan 2014 · TMS Light Metals
  • J.-M. Drezet · P. Celle · O. Ribaud · T. Pirling
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    ABSTRACT: During casting, thermally induced deformations give birth to ingot distortions and residual stresses. For some high strength alloys, ingot cracking can happen during casting per se or during cooling down. Ingot distortions such as rolling face pull-in, but curl and but swell are rather easy to quantify as opposed to internal stresses. As aluminium is rather transparent to neutrons, residual stress measurements using neutron diffraction appeared to be a good way to validate the thermomechanical models aimed at simulating the stress build-up during casting. This technique has been applied to DC cast AA7050 rolling plate ingots with special attention to the stress generation in the transient start-up phase, i.e. in the foot of the ingot. Additional results using the hole drilling method complement the measurements. The measured stress distributions are compared with the results of a numerical model of DC casting for ingots cast with and without a wiper.
    No preview · Article · Jan 2014
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    Nasim Jamaly · A. B. Phillion · J.-M. Drezet
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    ABSTRACT: The occurrence of hot tearing during the industrial direct chill (DC) casting process results in significant quality issues and a reduction in productivity. In order to investigate their occurrence, a new semisolid constitutive law (Phillion et al.) for AA5182 that takes into account cooling rate, grain size, and porosity has been incorporated within a DC casting finite element process model for round billets. A hot tearing index was calculated from the semisolid strain predictions from the model. This hot tearing index, along with semisolid stress–strain predictions from the model, was used to perform a sensitivity analysis on the relative effects of microstructural features (e.g., grain size, coalescence temperature) as well as process parameters (e.g., casting speed) on hot tearing. It was found that grain refinement plays an important role in the formation of hot cracks. In addition, the combination of slow casting speeds and a low temperature for mechanical coalescence was found to improve hot tearing resistance.
    Preview · Article · Oct 2013 · Metallurgical and Materials Transactions B
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    M. Sistaninia · S. Terzi · A.B. Phillion · J.-M. Drezet · M. Rappaz
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    ABSTRACT: The mechanical behavior of partially solidified Al–Cu alloys is investigated to assess the influence of mushy zone deformation on hot tearing. For this purpose, the results of a semi-solid tensile test conducted in situ using X-ray microtomography are compared with the predictions of a coupled hydromechanical granular model in order to both validate the predictions of the model and explain the experimental observations. It is shown that hot tears initiate in the widest liquid channels connected to the free (oxidized) surfaces as long as there is contact between the intergranular liquid and the ambient air. The necking behavior is associated with the deformation-induced liquid pressure drop. Overall, the stresses predicted by the granular model under tensile and shear deformations agree well with the experimental data. Thus, the granular model achieves an important step in predicting hot tearing formation.
    Full-text · Dataset · Aug 2013
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    ABSTRACT: A coupled hydromechanical granular model aimed at predicting hot tear formation and stress–strain behavior in metallic alloys during solidification is applied to the semicontinuous direct chill casting of aluminum alloy round billets. This granular model consists of four separate three-dimensional (3D) modules: (I) a solidification module that is used for generating the solid–liquid geometry at a given solid fraction, (II) a fluid flow module that is used to calculate the solidification shrinkage and deformation-induced pressure drop within the intergranular liquid, (III) a semisolid deformation module that is based on a combined finite element/discrete element method and simulates the rheological behavior of the granular structure, and (IV) a failure module that simulates crack initiation and propagation. To investigate hot tearing, the granular model has been applied to a representative volume within the direct chill cast billet that is located at the bottom of the liquid sump, and it reveals that semisolid deformations imposed on the mushy zone open the liquid channels due to localization of the deformation at grains boundaries. At a low casting speed, only individual pores are able to form in the widest channels because liquid feeding remains efficient. However, as the casting speed increases, the flow of liquid required to compensate for solidification shrinkage also increases and as a result the pores propagate and coalesce to form a centerline crack.
    Full-text · Article · Aug 2013 · JOM: the journal of the Minerals, Metals & Materials Society
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    J.-M. Drezet · M. Rappaz · J.-L. Anjier
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    ABSTRACT: This chapter contains sections titled: Introduction The RDG hot tearing criterion Solidification path of an AA6063 alloy Application to the DC casting of round billets Sensitivity to the casting speed The Clyne and Davies criterion Conclusion Acknowledgment
    Full-text · Article · Apr 2013
  • M. Sistaninia · J.-M. Drezet · A.B. Phillion · M. Rappaz
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    ABSTRACT: A coupled hydromechanical granular model aimed at predicting hot tear formation and stress–strain behavior in metallic alloys during solidification is applied to the semicontinuous direct chill casting of aluminum alloy round billets. This granular model consists of four separate three-dimensional (3D) modules: (I) a solidification module that is used for generating the solid–liquid geometry at a given solid fraction, (II) a fluid flow module that is used to calculate the solidification shrinkage and deformation-induced pressure drop within the intergranular liquid, (III) a semisolid deformation module that is based on a combined finite element/discrete element method and simulates the rheological behavior of the granular structure, and (IV) a failure module that simulates crack initiation and propagation. To investigate hot tearing, the granular model has been applied to a representative volume within the direct chill cast billet that is located at the bottom of the liquid sump, and it reveals that semisolid deformations imposed on the mushy zone open the liquid channels due to localization of the deformation at grains boundaries. At a low casting speed, only individual pores are able to form in the widest channels because liquid feeding remains efficient. However, as the casting speed increases, the flow of liquid required to compensate for solidification shrinkage also increases and as a result the pores propagate and coalesce to form a centerline crack.
    No preview · Conference Paper · Jan 2013
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    M. Sistaninia · S. Terzi · A.B. Phillion · J.-M. Drezet · M. Rappaz
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    ABSTRACT: The mechanical behavior of partially solidified Al–Cu alloys is investigated to assess the influence of mushy zone deformation on hot tearing. For this purpose, the results of a semi-solid tensile test conducted in situ using X-ray microtomography are compared with the predictions of a coupled hydromechanical granular model in order to both validate the predictions of the model and explain the experimental observations. It is shown that hot tears initiate in the widest liquid channels connected to the free (oxidized) surfaces as long as there is contact between the intergranular liquid and the ambient air. The necking behavior is associated with the deformation-induced liquid pressure drop. Overall, the stresses predicted by the granular model under tensile and shear deformations agree well with the experimental data. Thus, the granular model achieves an important step in predicting hot tearing formation.
    Full-text · Article · Jan 2013 · Acta Materialia
  • N. Chobaut · R. Le Jallé · Denis Carron · P. Saelzle · Jean Marie Drezet

    No preview · Article · Jan 2013
  • N. Chobaut · J. Repper · T. Pirling · Denis Carron · P. Saelzle · Jean Marie Drezet

    No preview · Article · Jan 2013
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    M. Sistaninia · A.B. Phillion · J.-M. Drezet · M. Rappaz
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    ABSTRACT: A three-dimensional (3-D) coupled hydromechanical granular model has been developed and validated to directly predict, for the first time, hot tear formation and stress–strain behavior in metallic alloys during solidification. This granular model consists of four separate 3-D modules: (i) the solidification module is used to generate the solid–liquid geometry at a given solid fraction; (ii) the fluid flow module (FFM) is used to calculate the solidification shrinkage and deformation-induced pressure drop within the intergranular liquid; (iii) the semi-solid deformation module (SDM) simulates the rheological behavior of the granular structure; and (iv) the failure module (FM) simulates crack initiation and propagation. Since solid deformation, intergranular flow and crack initiation are deeply linked together, the FFM, SDM and FM are coupled processes. This has been achieved through the development of a new three-phase interactive technique that couples the interaction between intergranular liquid, solid grains and growing voids. The results show that the pressure drop, and consequently hot tear formation, depends also on the compressibility of the mushy zone skeleton, in addition to the well-known contributors (lack of liquid feeding and semi-solid deformation).
    Full-text · Article · Nov 2012 · Acta Materialia
  • N. Chobaut · J. Repper · T. Pirling · D. Carron · J.M. Drezet
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    ABSTRACT: In the current trend toward thicker aluminium plates, a major concern is the generation of high internal stresses during quenching, which can cause distortions during machining and pose serious safety concerns. Although the material is stretched after quench, substantially reducing residual stresses, they are not fully suppressed. In addition, the cooling rate is not large enough at the core of such thick plates to prevent any precipitation. This has a great impact on the efficiency of ageing. In this work, residual stress distributions in a heat-treatable aluminium alloy AA7449 thick plate in the as-quenched state measured by neutron diffraction are presented. A comparison between single (311) diffraction peak and multiple peaks analysis using Pawley algorithm is shown. The variation of the stress free reference value through the plate thickness is discussed and measured stresses are compared with residual stresses predicted by a thermo- mechanical finite element model of quenching.
    No preview · Chapter · Jun 2012
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    J.-M Drezet · Th Pirling · C Jaquerod
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    ABSTRACT: IntroductionMaterial and residual stress measurement techniquesResults and DiscussionsConclusion Acknowledgements
    Preview · Article · May 2012 · TMS Light Metals