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Papers by Gouenou Girardin
HAL (Le Centre pour la Communication Scientifique Directe), May 27, 2009
Acta Materialia, 2015
ABSTRACT Various forms of the plastic deformation in single crystals are studied in pure and hydr... more ABSTRACT Various forms of the plastic deformation in single crystals are studied in pure and hydrogen-containing nickel and nickel alloys oriented for single slip [1 3 5] and strained in the stage III regime (shear strain, γ = 0.8). The heterogeneity of deformation is investigated at two distinct scales: slip bands and dislocation structures, using atomic force microscopy (AFM) and transmission electronic microscopy (TEM). Size and distribution of slip band thicknesses and geometrically necessary boundary (GNB) spacing are comparable. GNB structures both screen the long-range stress fields and decrease the mean free path of mobile dislocations, whereas equiaxed cells only impede dislocation motion through their role as obstacles. Consequently, GNB formation localizes deformation in specific slip bands. Additionally, the observed similarity between GNB spacing and equiaxed cell size suggests a correlation between these microstructural features. The impact of solid solution atoms on the inter-wall spacing is established for chromium and hydrogen. Both decrease the GNB spacing because of a decrease of the cross-slip probability and stacking fault energy, combined to a shielding effect for the later. The effect of GNB spacing on strain hardening is discussed in terms of the length scale associated with GNBs and the effect of solute content.
Environment-Induced Cracking of Materials, 2008
Publisher Summary This chapter examines the effect of solute drag on the flow stress of hydrogen-... more Publisher Summary This chapter examines the effect of solute drag on the flow stress of hydrogen-containing nickel and Ni-Cr. The static strain ageing (SSA) experiments provide the quantitative data to evaluate this phenomenon. The maximum pinning stress increases with hydrogen concentration in pure Ni and Ni-16Cr. At room temperature, the corresponding solute drag yields a hardening contribution to the flow stress, up to 20 MPa for a concentration of 1900 at.ppm. Incorporating the shielding of pair interactions into classical results of the dislocation theory, an analytical expressions is proposed for the effect of solute hydrogen on the mechanisms and dislocation properties: the line energy and line tension of curved dislocations, the critical shear stress for the expansion of a dislocation loop, and the cross-slip of screw dislocation. Based on these analytical results, numerical simulations are developed to evaluate the role of hydrogen on the activity of a Frank-Read source and on the stability of dislocation junctions. The detailed modeling provides quantitative tools for interpreting the mechanical testing of hydrogen-containing samples in terms of dislocation mechanisms.
Scripta Materialia, 2004
ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning f... more ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning force as a function of the hydrogen concentration in hydrogenated nickel and binary nickel—16 wt% chromium. The role of hydrogen transport by mobile dislocations on hydrogen embrittlement is demonstrated.
Within the framework of the ANTARES program, AREVA NP, EDF and the CEA have launched a joint R&D ... more Within the framework of the ANTARES program, AREVA NP, EDF and the CEA have launched a joint R&D program on metallic materials for VHTR. Reference alloys for circuit and Intermediate Heat eXchanger (IHX) are nickel-based with about 22%wt. of chromium. Compatibility with the HTR primary helium appears to be a determining property for the material selection and qualification. The coolant is actually polluted by a low level of impurities that can interact with metals at high temperature. Oxidation, carburization and/or decarburization occur, in relation to atmosphere characteristics, temperature and alloy chemical composition. As these corrosion effects can notably influence the mechanical properties, they often are determining to the component service life. Since the corrosion behavior is highly sensitive to environmental conditions, material studies require dedicated facilities that shall allow for a strict control of the environment throughout the entire specimen exposure. AREVA NP,...
Nous evaluons les differentes contributions des interactions hydrogene-dislocations sur la plasti... more Nous evaluons les differentes contributions des interactions hydrogene-dislocations sur la plasticite de materiaux CFC hydrogenes afin d'alimenter des modeles predictifs d'endommagement par corrosion sous contrainte par des essais de vieillissement, nous quantifions la contribution positive a la contrainte d'ecoulement du trainage des atmospheres de solutes par les dislocations. Nous demontrons le role du transport de l'hydrogene par les dislocations dans le mecanisme de fragilisation. Nous modelisons l'influence de l'ecrantage du champ elastique des dislocations par l'hydrogene sur les mecanismes elementaires de la plasticite et montrons que la diminution de la probabilite de glissement devie resulte de l'action conjuguee d'effets elastiques et de coeur. Les essais sur monocristaux demontrent la contribution preponderante des effets sur le glissement de vie. Les essais de traction sur des polycristaux illustrent la diversite des reponses macrosco...
Materials and Corrosion, 2008
Nickel-base superalloys are commonly used for high-temperature applications in power-generation i... more Nickel-base superalloys are commonly used for high-temperature applications in power-generation industry, e.g., gas-turbine blades or heat exchangers. They are designed to resist high creep loading and severe corrosion attack during operation. Nitridation is one of these corrosion processes, in particular when the alloys need to be exposed to a N 2 atmosphere. Based on past assumptions, a dense oxide layer should be an efficient barrier against N 2 ingress. But is this really the case? This work is focused on the nitridation behavior of commercial Ni-base alloys and the influence of a pre-oxidation treatment. To model the growth of the internal-nitridation zone, the diffusion processes were solved using the numerical implicit finite-difference method in combination with the subroutine ChemApp for thermodynamic calculations.
Acta Materialia, 2015
Various forms of the plastic deformation in single crystals are studied in pure and hydrogenconta... more Various forms of the plastic deformation in single crystals are studied in pure and hydrogencontaining nickel and nickel alloys oriented for single slip [135] and strained in the stage III regime (shear strain, γ ≈ 0.8). The heterogeneity of deformation is investigated at two distinct scales: slip bands and dislocation structures, using atomic force microscopy (AFM) and transmission electronic microscopy (TEM). Size and distribution of slip band thicknesses and geometrically necessary boundary (GNB) spacing are comparable. GNB structures both screen the long-range stress fields and decrease the mean free path of mobile dislocations, whereas equiaxed cells only impede dislocation motion through their role as obstacles. Consequently, GNB formation localizes deformation in specific slip bands. Additionally, the observed similarity between GNB spacing and equiaxed cells size suggests a correlation between these microstructural features. The impact of solid solution atoms on the inter-wall spacing is established for chromium and hydrogen. Both decrease the GNB spacing because of a decrease of the cross-slip probability and stacking fault energy, combined to a shielding effect for the later. The effect of GNB spacing on strain hardening is discussed in term of the length scale associated with GNBs and the effect of solute content.
Environment-Induced Cracking of Materials, 2008
Scripta Materialia, 2004
ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning f... more ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning force as a function of the hydrogen concentration in hydrogenated nickel and binary nickel—16 wt% chromium. The role of hydrogen transport by mobile dislocations on hydrogen embrittlement is demonstrated.
The effect of hydrogen on tensile tests of nickel and binary nickel -16 wt. % chromium is analyse... more The effect of hydrogen on tensile tests of nickel and binary nickel -16 wt. % chromium is analysed in terms of solute drag phenomenon. Static Strain Ageing experiments are used to measure the saturated dislocation pinning force as a function of the H concentration. First order hydrogen -dislocation interactions causes a shielding of the pair interactions between edge dislocations. The influence of this screening effect is analytically evaluated on the selfenergy and line tension of curved dislocations, the critical force for the expansion of a dislocation loop and the dissociation mechanism. These results are used to interpret experimental results on the plastic flow of hydrogen-charged nickel single crystals oriented for easy glide. This study illustrates the mechanisms of H -dislocation interactions and their consequences on the different contributions of hydrogen to the flow stress of nickel.
Environment-Induced Cracking of Materials, 2008
HAL (Le Centre pour la Communication Scientifique Directe), May 27, 2009
Acta Materialia, 2015
ABSTRACT Various forms of the plastic deformation in single crystals are studied in pure and hydr... more ABSTRACT Various forms of the plastic deformation in single crystals are studied in pure and hydrogen-containing nickel and nickel alloys oriented for single slip [1 3 5] and strained in the stage III regime (shear strain, γ = 0.8). The heterogeneity of deformation is investigated at two distinct scales: slip bands and dislocation structures, using atomic force microscopy (AFM) and transmission electronic microscopy (TEM). Size and distribution of slip band thicknesses and geometrically necessary boundary (GNB) spacing are comparable. GNB structures both screen the long-range stress fields and decrease the mean free path of mobile dislocations, whereas equiaxed cells only impede dislocation motion through their role as obstacles. Consequently, GNB formation localizes deformation in specific slip bands. Additionally, the observed similarity between GNB spacing and equiaxed cell size suggests a correlation between these microstructural features. The impact of solid solution atoms on the inter-wall spacing is established for chromium and hydrogen. Both decrease the GNB spacing because of a decrease of the cross-slip probability and stacking fault energy, combined to a shielding effect for the later. The effect of GNB spacing on strain hardening is discussed in terms of the length scale associated with GNBs and the effect of solute content.
Environment-Induced Cracking of Materials, 2008
Publisher Summary This chapter examines the effect of solute drag on the flow stress of hydrogen-... more Publisher Summary This chapter examines the effect of solute drag on the flow stress of hydrogen-containing nickel and Ni-Cr. The static strain ageing (SSA) experiments provide the quantitative data to evaluate this phenomenon. The maximum pinning stress increases with hydrogen concentration in pure Ni and Ni-16Cr. At room temperature, the corresponding solute drag yields a hardening contribution to the flow stress, up to 20 MPa for a concentration of 1900 at.ppm. Incorporating the shielding of pair interactions into classical results of the dislocation theory, an analytical expressions is proposed for the effect of solute hydrogen on the mechanisms and dislocation properties: the line energy and line tension of curved dislocations, the critical shear stress for the expansion of a dislocation loop, and the cross-slip of screw dislocation. Based on these analytical results, numerical simulations are developed to evaluate the role of hydrogen on the activity of a Frank-Read source and on the stability of dislocation junctions. The detailed modeling provides quantitative tools for interpreting the mechanical testing of hydrogen-containing samples in terms of dislocation mechanisms.
Scripta Materialia, 2004
ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning f... more ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning force as a function of the hydrogen concentration in hydrogenated nickel and binary nickel—16 wt% chromium. The role of hydrogen transport by mobile dislocations on hydrogen embrittlement is demonstrated.
Within the framework of the ANTARES program, AREVA NP, EDF and the CEA have launched a joint R&D ... more Within the framework of the ANTARES program, AREVA NP, EDF and the CEA have launched a joint R&D program on metallic materials for VHTR. Reference alloys for circuit and Intermediate Heat eXchanger (IHX) are nickel-based with about 22%wt. of chromium. Compatibility with the HTR primary helium appears to be a determining property for the material selection and qualification. The coolant is actually polluted by a low level of impurities that can interact with metals at high temperature. Oxidation, carburization and/or decarburization occur, in relation to atmosphere characteristics, temperature and alloy chemical composition. As these corrosion effects can notably influence the mechanical properties, they often are determining to the component service life. Since the corrosion behavior is highly sensitive to environmental conditions, material studies require dedicated facilities that shall allow for a strict control of the environment throughout the entire specimen exposure. AREVA NP,...
Nous evaluons les differentes contributions des interactions hydrogene-dislocations sur la plasti... more Nous evaluons les differentes contributions des interactions hydrogene-dislocations sur la plasticite de materiaux CFC hydrogenes afin d'alimenter des modeles predictifs d'endommagement par corrosion sous contrainte par des essais de vieillissement, nous quantifions la contribution positive a la contrainte d'ecoulement du trainage des atmospheres de solutes par les dislocations. Nous demontrons le role du transport de l'hydrogene par les dislocations dans le mecanisme de fragilisation. Nous modelisons l'influence de l'ecrantage du champ elastique des dislocations par l'hydrogene sur les mecanismes elementaires de la plasticite et montrons que la diminution de la probabilite de glissement devie resulte de l'action conjuguee d'effets elastiques et de coeur. Les essais sur monocristaux demontrent la contribution preponderante des effets sur le glissement de vie. Les essais de traction sur des polycristaux illustrent la diversite des reponses macrosco...
Materials and Corrosion, 2008
Nickel-base superalloys are commonly used for high-temperature applications in power-generation i... more Nickel-base superalloys are commonly used for high-temperature applications in power-generation industry, e.g., gas-turbine blades or heat exchangers. They are designed to resist high creep loading and severe corrosion attack during operation. Nitridation is one of these corrosion processes, in particular when the alloys need to be exposed to a N 2 atmosphere. Based on past assumptions, a dense oxide layer should be an efficient barrier against N 2 ingress. But is this really the case? This work is focused on the nitridation behavior of commercial Ni-base alloys and the influence of a pre-oxidation treatment. To model the growth of the internal-nitridation zone, the diffusion processes were solved using the numerical implicit finite-difference method in combination with the subroutine ChemApp for thermodynamic calculations.
Acta Materialia, 2015
Various forms of the plastic deformation in single crystals are studied in pure and hydrogenconta... more Various forms of the plastic deformation in single crystals are studied in pure and hydrogencontaining nickel and nickel alloys oriented for single slip [135] and strained in the stage III regime (shear strain, γ ≈ 0.8). The heterogeneity of deformation is investigated at two distinct scales: slip bands and dislocation structures, using atomic force microscopy (AFM) and transmission electronic microscopy (TEM). Size and distribution of slip band thicknesses and geometrically necessary boundary (GNB) spacing are comparable. GNB structures both screen the long-range stress fields and decrease the mean free path of mobile dislocations, whereas equiaxed cells only impede dislocation motion through their role as obstacles. Consequently, GNB formation localizes deformation in specific slip bands. Additionally, the observed similarity between GNB spacing and equiaxed cells size suggests a correlation between these microstructural features. The impact of solid solution atoms on the inter-wall spacing is established for chromium and hydrogen. Both decrease the GNB spacing because of a decrease of the cross-slip probability and stacking fault energy, combined to a shielding effect for the later. The effect of GNB spacing on strain hardening is discussed in term of the length scale associated with GNBs and the effect of solute content.
Environment-Induced Cracking of Materials, 2008
Scripta Materialia, 2004
ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning f... more ABSTRACT Static strain ageing experiments are used to measure the saturated dislocation pinning force as a function of the hydrogen concentration in hydrogenated nickel and binary nickel—16 wt% chromium. The role of hydrogen transport by mobile dislocations on hydrogen embrittlement is demonstrated.
The effect of hydrogen on tensile tests of nickel and binary nickel -16 wt. % chromium is analyse... more The effect of hydrogen on tensile tests of nickel and binary nickel -16 wt. % chromium is analysed in terms of solute drag phenomenon. Static Strain Ageing experiments are used to measure the saturated dislocation pinning force as a function of the H concentration. First order hydrogen -dislocation interactions causes a shielding of the pair interactions between edge dislocations. The influence of this screening effect is analytically evaluated on the selfenergy and line tension of curved dislocations, the critical force for the expansion of a dislocation loop and the dissociation mechanism. These results are used to interpret experimental results on the plastic flow of hydrogen-charged nickel single crystals oriented for easy glide. This study illustrates the mechanisms of H -dislocation interactions and their consequences on the different contributions of hydrogen to the flow stress of nickel.
Environment-Induced Cracking of Materials, 2008