irradiation induced loops in zirconium alloys studied by in situ - PowerPoint PPT Presentation

Interaction between dislocation and irradiation induced loops in zirconium alloys studied by in situ straining experiments in TEM, molecular and dislocation dynamics simulations F. Onimus 1 , L. Dupuy 1 , M. Gaumé 1 , W. Kassem 1 , F. Mompiou 2 1 Service de recherches Métallurgiques Appliquées, CEA, Université Paris- Saclay, 91191 Gif-sur-Yvette, France 2 Centre d'Elaboration de Matériaux et d'Etudes Structurales, CNRS, 29 Rue Jeanne Marvig, 31055 Toulouse, France This work has been funded by the project GAINE from the French nuclear tripartite institute CEA EDF Framatome. The development of Dislocation Dynamics has been funded by the French Agence Nationale de la Recherche (ANR). 19th International Symposium on Zirconium in the Nuclear Industry 19 – 23 May 2019 | Manchester, UK

Radiation effects on the mechanical behavior Fuel rod Internal pressure test at 350°C 600 Irradiated Zy-4 Rx non irradié Non irradiated 500 circonférentielle (MPa) Irradiated Zy-4 Rx irradié Hoop stress (MPa) Necking 400 Contrainte Non irradiated 300 Water T=320°C, Necking 200 P=155 bar 100 0 0% 2% 4% 6% 8% 10% 12% Hoop strain (%) Déformation circonférentielle Fast → Irradiation induced hardening neutrons → Decrease of the uniform elongation (early necking but ductile failure mode) What is the origin of the change in the mechanical behavior ? Need for an understanding and prediction of the effect of irradiation on mechanical behavior 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 2

Radiation effects on the microstructure Fast neutrons → Creation of point defects b & point defect clusters n Dislocation loop Displacement cascade Point defect clusters in zirconium: <a>-loops & <c>-loops → High density of 10 nm small <a>-loops 50 nm <a>-loops, Vacancy and Insterstitial <c>-loops, only Vacancy loops <a>-loops are believed to act as obstacles against dislocation glide → explaining the radiation induced hardening 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 3

Dislocation channelling mechanism After transverse tensile test at 350°C Thin foil Channel → Clearing of loops by gliding dislocations for sufficient applied stress F. Onimus, J.-L. Béchade, D. Gilbon (2013) Metall. and Mater. Trans. 44 (1) 45 – 60. F. Onimus, J.-L. Béchade, C. Prioul, P. Pilvin et al. (2005) ASTM STP 1467, 14th B10 Int. Symp. 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 4 F. Onimus, I. Monnet, J.-L. Béchade, et al. (2004) J. Nucl. Mater. 328 (2-3) 165-179.

TEM observations after Transverse Tensile test at 350 ° C After neutron irradiation + testing Non irradiated + testing c Pyramidal P 1 Specimen 1 Grain 2 b=<c+a> Prismatic P a 2 a 1 1 µm b=<a> a 3 Basal B Observation of Basal channels, no prismatic channel → Change of the easy glide slip system ! . 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 5

TEM observations after Internal Pressure test at 350 ° C Specimen 2 Specimen 2 Grain 1 Grain 3 g=0002 Observation of Basal channels. No prismatic channel. 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 6

TEM observations after Axial Tensile test at 350 ° C (z) (q) {0002} pole figure → the Basal slip systems are not well orientated → Activation of Prismatic slip Prismatic channels (+pyramidal), no B channel → More difficult activation of Prismatic glide after irradiation and only partial clearing of loops. 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 7

A Multi-Scale Approach Mechanical tests TEM observations of grains → Mechanical behavior → Deformation mechanisms → Study of interactions between dislocation and loops to understand the observed deformation mechanisms Dislocation Dynamics Molecular Dynamics In situ straining in TEM → Towards more complex → Details of dislocation – loop vs. Dislocation Dynamics and larger configurations interactions 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 8

Molecular & Dislocation Dynamics simulations Following the work done by Serra & Bacon → MD simulations of interactions between loops and dislocation (only edge/screw dislocations in prismatic plane) [Serra, A., & Bacon, D. J. (2013). Modelling and Simulation in Materials Science and Engineering, 21(4)] → Need for higher length scale simulations → Dislocation dynamics Molecular Dynamics Dislocation Dynamics LAMMPS LAMMPS 6,000,000 DoF 300 DoF Elastic coefficients, DoF: Degree of Freedom mobility coefficients & → Atomic scale informed Dislocation Dynamics simulations 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 9 dislocation core energy.

Molecular & Dislocation Dynamics simulations Mobility coefficient measurement from MD simulations for « unjogged » and « jogged » edge dislocations gliding in the prismatic plane 𝑤 = 𝜐𝑐 𝐶 Modeling of the effective friction coefficient of a jogged dislocation: Friction coefficient Value ℎ 𝑘𝑝𝑕 2.96×10 -5 Pa.s 𝐶 𝑄 𝐶 𝑓𝑔𝑔 = 𝐶 𝑄 + 𝜍 𝑜 𝐶 𝐶 + 𝑞 2 4.56×10 -5 Pa.s 𝐶 𝐶 𝜍 𝑜 = 𝑜/𝑀 1.72×10 -13 Pa.s.m 𝑞 (Number of constricted nodes per unit length) Taking into account additional friction on the constricted nodes ( p ) → DD simulation are parametrized on MD simulations 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 10

Detailed comparison of dislocation – loop interactions Dislocation Dynamics vs. Molecular Dynamics Edge dislocation Screw dislocation Prismatic Prismatic LAMMPS Same Burgers vectors LAMMPS Different Burgers vectors → Validation of the Dislocation Dynamics LAMMPS by detailed comparison with Molecular Dynamics simulations on pure screw/edge dislocations in the prismatic plane → Study of more complex configurations using DD simulations 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 11

A Multi-Scale Approach Mechanical tests TEM observations of grains → Mechanical behavior → Deformation mechanisms → Need for a better understanding of the interactions between dislocation and loops to understand the observed deformation mechanisms Dislocation Dynamics Molecular Dynamics In situ straining in TEM → Towards more complex → Details of dislocation – loop vs. Dislocation Dynamics and larger configurations interactions 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 12

Simulations of complex configurations Dislocation Dynamics simulations of mixed dislocations gliding either in the prismatic or basal planes and interacting with loops b G =b 2 Edge type 𝜏 23 y interaction Mixed type interaction b L =b 2 Screw type q x interaction 𝜏 23 Large Frank-Read dislocation source - dislocation loop 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 13

Simulations of complex configurations Dislocation Dynamics simulations of mixed dislocations gliding either in the prismatic or basal planes and interacting with loops b G =b 2 Edge type y interaction Mixed type interaction b L =b 2 Screw type q x interaction 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 14

Simulations of dislocations gliding in Prismatic Plane Screw type interaction, same Burgers vectors (b L =b G ) b G =b 2 b L =b 2 𝜾 = 𝟐𝟏° → Strong pinning / No clearing 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 15

Simulations of dislocations gliding in Prismatic Plane Screw type interaction, different Burgers vectors (b L =b 1, b G =b 2 ) b G =b 2 b L =b 1 𝜾 = 𝟑𝟐° → Strong pinning / No clearing 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 16

Simulations of dislocations gliding in Prismatic Plane Edge type interaction, same Burgers vectors (b L =b G ) b G =b 2 b L =b 2 𝜾 = 𝟖𝟑° → Partial clearing / No pinning 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 17

Simulations of dislocations gliding in Prismatic Plane Edge type interaction, different Burgers vectors (b L =b 1, b G =b 2 ) b G =b 2 b L =b 1 𝜾 = 𝟖𝟑° → Full clearing / No pinning 19th International Symposium on Zirconium in the Nuclear Industry, 19 – 23 May 2019 | Manchester, UK F. Onimus 18