J.-M. Drezet

École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

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Publications (65)69.71 Total impact

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    N. Chobaut · D. Carron · S. Arsène · P. Schloth · J.-M. Drezet
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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.
    Journal of Materials Processing Technology 08/2015; 222. DOI:10.1016/j.jmatprotec.2015.03.029 · 1.95 Impact Factor
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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.
    Applied Physics Letters 09/2014; 105(10). DOI:10.1063/1.4894768 · 3.52 Impact Factor
  • 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%.
    Journal of Materials Processing Technology 07/2014; 214(7):1372–1378. DOI:10.1016/j.jmatprotec.2014.02.011 · 2.04 Impact Factor
  • 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.
    Materials Science Forum 06/2014; 794-796:901-925. DOI:10.4028/www.scientific.net/MSF.794-796.921
  • D. Heydari · A. Shahkaram Fard · A. Bakhshi · J.M. Drezet
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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.
    Journal of Materials Processing Technology 03/2014; 214(3):681–687. DOI:10.1016/j.jmatprotec.2013.10.001 · 1.95 Impact Factor
  • 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.
    Metallurgical and Materials Transactions B 10/2013; 44(5). DOI:10.1007/s11663-013-9902-0 · 1.46 Impact Factor
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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.
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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.
    JOM: the journal of the Minerals, Metals & Materials Society 08/2013; 65:1131-37. DOI:10.1007/s11837-013-0662-8 · 1.76 Impact Factor
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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
  • 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.
    JOM; 01/2013
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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.
    Acta Materialia 01/2013; 61:3831-3841. · 4.47 Impact Factor
  • N. Chobaut · J. Repper · T. Pirling · Denis Carron · P. Saelzle · Jean Marie Drezet
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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).
    Acta Materialia 11/2012; 60:6793-6803. DOI:10.1016/j.actamat.2012.08.057 · 4.47 Impact Factor
  • 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.
    ICAA13: 13th International Conference on Aluminum Alloys, Edited by Hasso Weiland, Anthony D. Rollett, William A. Cassada, 06/2012: chapter Residual Stress Analysis in AA7449 As-Quenched Thick Plates Using Neutrons and FE Modelling: pages 285-291; John Wiley & Sons, Inc, Hoboken, NJ, USA., ISBN: 978111849529
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    M. Sistaninia · A.B. Phillion · J.-M. Drezet · M. Rappaz
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    ABSTRACT: A three-dimensional (3-D) granular model which simulates fluid flow within solidifying alloys with a globular microstructure, such as that found in grain refined Al alloys, is presented. The model geometry within a representative volume element (RVE) consists of a set of prismatic triangular elements representing the intergranular liquid channels. The pressure field within the liquid channels is calculated using a finite elements (FEs) method assuming a Poiseuille flow within each channel and flow conservation at triple lines. The fluid flow is induced by solidification shrinkage and openings at grain boundaries due to deformation of the coherent solid. The granular model predictions are validated against bulk data calculated with averaging techniques. The results show that a fluid flow simulation of globular semi-solid materials is able to reproduce both a map of the 3-D intergranular pressure and the localization of feeding within the mushy zone. A new hot cracking sensitivity coefficient is then proposed. Based on a mass balance performed over a solidifying isothermal volume element, this coefficient accounts for tensile deformation of the semi-solid domain and for the induced intergranular liquid feeding. The fluid flow model is then used to calculate the pressure drop in the mushy zone during the direct chill casting of aluminum alloy billets. The predicted pressure demonstrates that deep in the mushy zone where the permeability is low the local pressure can be significantly lower than the pressure predicted by averaging techniques .
    Acta Materialia 05/2012; 60:3902-3911. DOI:10.1016/j.actamat.2012.03.036 · 4.47 Impact Factor
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    J.-M Drezet · A Evans · T Pirling · B Pitié
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    ABSTRACT: Stress relief treatment before machining and sawing aluminium direct chill cast products is required to avoid uncontrolled distortion, crack formation and significant safety concerns due to the presence of thermally induced residual stresses created during casting. Numerical models have been developed to compute these residual stresses and yet have only been validated against measured surface distortions. In the present contribution, the variations in residual strains and stresses have been measured using neutron diffraction and hole drilling strain gage in two AA 6063 grain refined cylindrical billet sections cast at two casting speeds. The measured residual stresses compare favourably with the numerical model, in particular the depth at which the axial and hoop stresses change sign. Such results provide insight into the development of residual stresses within castings and show that the stored elastic energy varies linearly with the casting speed, at least within the range of speeds that correspond to production conditions.
    International Journal of Cast Metals Research 04/2012; 25(2). DOI:10.1179/1743133611Y.0000000029 · 0.51 Impact Factor
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    N Jamaly · A B Phillion · S L Cockcroft · J.-M Drezet
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    ABSTRACT: Hot tearing and loss of dimensional stability are two key defects related to industrial aluminum alloy casting processes. In order to investigate their occurrence, a new semi-solid constitutive law [20] for AA5182 that takes into account cooling rate, grain size and porosity has been implemented into a Direct Chill casting process model for round billets. The semi-solid stress-strain predictions provided by this new constitutive law as well as the effects of processing parameters were then examined to demonstrate the relationships between defect formation, microstructure, and processing variables.
    TMS (The Minerals, Metals & Materials Society) Annual Meeting, Orlando, Florida, USA; 03/2012
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    J.-M Drezet · Th Pirling · C Jaquerod
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    ABSTRACT: Stress relief treatment is often required prior to sawing aluminum DC cast products in order to prevent crack formation and significant safety concerns due to the presence of high residual stresses generated during casting. Numerical models have been developed to compute these residual stresses and yet have only been validated against measured surface distortions. In the present contribution, the variation in residual strains and stresses have been measured using neutron diffraction in two AA6063 grain-refined cylindrical billet sections cast at two casting speeds. The measured residual stresses compare favorably with the numerical model, in particular the depth at which the axial and hoop stresses change sign. Such results provide insight into the development of residual stresses within castings and show that the stored elastic energy varies linearly with the casting speed, at least within the range of speeds that correspond to production conditions.
    TMS Light Metals 01/2012;
  • Applied Bionics and Biomechanics 01/2012; Accepted, February 2011. · 0.47 Impact Factor
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    ABSTRACT: The biomedical industry shows increasing interest in the joining of dissimilar metals, especially with the aim of developing devices that combine different mechanical and corrosive properties. As an example, nickel–titanium shape memory alloys joined to stainless steel are very promising for new invasive surgery devices, such as guidewires. A fracture mechanics study of such joined wires was carried out using in situ tensile testing and scanning electron microscopy imaging combined with chemical analysis, and revealed an unusual fracture behaviour at superelastic stress. Nanoindentation was performed to determine the mechanical properties of the welded area, which were used as an input for mechanical computation in order to understand this unexpected behaviour. Automated image correlation allowed verification of the mechanical modelling and a reduced stress–strain model is proposed to explain the special fracture mechanism. This study reveals the fact that tremendous property changes at the interface between the NiTi base wire and the weld area have more impact on the ultimate tensile strength than the chemical composition variation across the welded area.
    Acta Materialia 10/2011; 59(17):6538-6546. DOI:10.1016/j.actamat.2011.06.031 · 4.47 Impact Factor