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

19th International Symposium on Zirconium in the Nuclear Industry 19–23 May 2019 | Manchester, UK

Interaction between dislocation and irradiation induced loops in zirconium alloys studied by in situ straining experiments in TEM, molecular and dislocation dynamics simulations

• F. Onimus1, L. Dupuy1, M. Gaumé1, W. Kassem1,
• F. Mompiou2

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).

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 2

100 200 300 400 500 600 0% 2% 4% 6% 8% 10% 12%

Déformation circonférentielle Contrainte circonférentielle (MPa)

Zy-4 Rx non irradié Zy-4 Rx irradié

Radiation effects on the mechanical behavior

Non irradiated Irradiated Necking Necking

Internal pressure test at 350°C

Hoop strain (%) Hoop stress (MPa)

Non irradiated Irradiated

Fuel rod

Fast neutrons Water T=320°C, P=155 bar

→ Irradiation induced hardening → Decrease of the uniform elongation (early necking but ductile failure mode)

Need for an understanding and prediction of the effect of irradiation on mechanical behavior What is the origin of the change in the mechanical behavior ?

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 3

Displacement cascade

Fast neutrons

n b

Dislocation loop

Radiation effects on the microstructure

→ Creation of point defects & point defect clusters Point defect clusters in zirconium: <a>-loops & <c>-loops

→ High density of small <a>-loops

<c>-loops, only Vacancy loops <a>-loops, Vacancy and Insterstitial

50 nm

10 nm

<a>-loops are believed to act as obstacles against dislocation glide → explaining the radiation induced hardening

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 4

Dislocation channelling mechanism

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.
• F. Onimus, I. Monnet, J.-L. Béchade, et al. (2004) J. Nucl. Mater. 328 (2-3) 165-179.

After transverse tensile test at 350°C

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 5

→ Change of the easy glide slip system !

TEM observations after Transverse Tensile test at 350°C

1 µm Non irradiated + testing

Pyramidal P1 Basal B Prismatic P

b=<c+a>

c

a2 a3 a1

b=<a>

After neutron irradiation + testing

Observation of Basal channels, no prismatic channel

. Specimen 1 Grain 2

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 6

Observation of Basal channels. No prismatic channel.

g=0002

TEM observations after Internal Pressure test at 350°C

Specimen 2 Grain 1 Specimen 2 Grain 3

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 7

(z)

(q)

→the Basal slip systems are not well orientated →Activation of Prismatic slip → More difficult activation of Prismatic glide after irradiation and only partial clearing of loops.

{0002} pole figure

Prismatic channels (+pyramidal), no B channel

TEM observations after Axial Tensile test at 350°C

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 8

A Multi-Scale Approach

TEM observations of grains →Deformation mechanisms Mechanical tests → Mechanical behavior

→ Study of interactions between dislocation and loops to understand the observed deformation mechanisms

Molecular Dynamics → Details of dislocation–loop interactions Dislocation Dynamics → Towards more complex and larger configurations In situ straining in TEM

• vs. Dislocation Dynamics

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 9

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)]

Molecular Dynamics

6,000,000 DoF

LAMMPS

→Need for higher length scale simulations → Dislocation dynamics

LAMMPS

Dislocation Dynamics

300 DoF → Atomic scale informed Dislocation Dynamics simulations

DoF: Degree of Freedom

Elastic coefficients, mobility coefficients & dislocation core energy.

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 10

Friction coefficient Value 𝐶𝑄 2.96×10-5 Pa.s 𝐶𝐶 4.56×10-5 Pa.s 𝑞 1.72×10-13 Pa.s.m

𝐶𝑓𝑔𝑔 = 𝐶𝑄 + 𝜍𝑜 𝐶𝐶 ℎ𝑘𝑝𝑕 2 + 𝑞 𝜍𝑜 = 𝑜/𝑀

Molecular & Dislocation Dynamics simulations

Mobility coefficient measurement from MD simulations for « unjogged » and « jogged » edge dislocations gliding in the prismatic plane Modeling of the effective friction coefficient of a jogged dislocation: Taking into account additional friction on the constricted nodes (p) → DD simulation are parametrized on MD simulations

(Number of constricted nodes per unit length)

𝑤 = 𝜐𝑐 𝐶

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 11

Detailed comparison of dislocation – loop interactions Dislocation Dynamics vs. Molecular Dynamics

Edge dislocation Screw dislocation Prismatic Prismatic

Different Burgers vectors Same Burgers vectors

LAMMPS LAMMPS LAMMPS

→ Validation of the Dislocation Dynamics by detailed comparison with Molecular Dynamics simulations on pure screw/edge dislocations in the prismatic plane → Study of more complex configurations using DD simulations

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 12

A Multi-Scale Approach

TEM observations of grains →Deformation mechanisms Mechanical tests → Mechanical behavior

→ Need for a better understanding of the interactions between dislocation and loops to understand the observed deformation mechanisms

Dislocation Dynamics → Towards more complex and larger configurations In situ straining in TEM

• vs. Dislocation Dynamics

Molecular Dynamics → Details of dislocation–loop interactions

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 13

𝜏23 𝜏23

y x

Screw type interaction Edge type interaction

q

Mixed type interaction

bL=b2 bG=b2

Simulations of complex configurations

Dislocation Dynamics simulations of mixed dislocations gliding either in the prismatic

• r basal planes and interacting with loops

Large Frank-Read dislocation source - dislocation loop

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 14

y x

Screw type interaction Edge type interaction

q

Mixed type interaction

bL=b2 bG=b2

Simulations of complex configurations

Dislocation Dynamics simulations of mixed dislocations gliding either in the prismatic

• r basal planes and interacting with loops

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 15

bG=b2 bL=b2 𝜾 = 𝟐𝟏°

→ Strong pinning / No clearing

Simulations of dislocations gliding in Prismatic Plane

Screw type interaction, same Burgers vectors (bL=bG)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 16

bG=b2 bL=b1 𝜾 = 𝟑𝟐°

→ Strong pinning / No clearing

Simulations of dislocations gliding in Prismatic Plane

Screw type interaction, different Burgers vectors (bL=b1, bG=b2)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 17

bG=b2 bL=b2 𝜾 = 𝟖𝟑°

→ Partial clearing / No pinning

Simulations of dislocations gliding in Prismatic Plane

Edge type interaction, same Burgers vectors (bL=bG)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 18

bG=b2 bL=b1 𝜾 = 𝟖𝟑°

→ Full clearing / No pinning

Simulations of dislocations gliding in Prismatic Plane

Edge type interaction, different Burgers vectors (bL=b1, bG=b2)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 19

For prismatic slip: Easy clearing of loops in the « edge-type » direction Strong pinning by loops in the « screw-type» direction

Simulations of dislocations gliding in Prismatic Plane

→ The expansion of the dislocation is impeded in the screw direction, leading to a difficult activation of prismatic slip. → Clearing of loops is restricted to the edge direction, leading to a difficult formation of dislocation channels. → This explains the TEM observations of difficult activation of prismatic slip after neutron irradiation and partially cleared channels in the prismatic plane.

Light blue domain : weak interaction, either partial clearing or no interaction depending on the height of the loop

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 20

bG=b2 bL=b2 𝜾 = 𝟐𝟏°

→ Strong pinning / No clearing

Simulations of dislocations gliding in Basal Plane

Screw type interaction, same Burgers vectors (bL=bG)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 21

bG=b2 bL=b1 𝜾 = 𝟐𝟏°

→ Weak pinning / No clearing

Simulations of dislocations gliding in Basal Plane

Screw type interaction, different Burgers vectors (bL=b1, bG=b2)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 22

bG=b2 bL=b3 𝜾 = 𝟔𝟓°

→ Full clearing / No pinning

Simulations of dislocations gliding in Basal Plane

Mixed type interaction, different Burgers vectors (bL=b3, bG=b2)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 23

bG=b2 bL=b2 𝜾 = 𝟗𝟓°

→ Partial clearing / No pinning

Simulations of dislocations gliding in Basal Plane

Edge type interaction, same Burgers vectors (bL=bG)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 24

bG=b2 bL=b1 𝜾 = 𝟗𝟓°

→ Pinning/ No clearing

Simulations of dislocations gliding in Basal Plane

Edge type interaction, different Burgers vectors (bL=b1, bG=b2)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 25

bG=b2 bL=b3 𝜾 = 𝟗𝟓°

→ Pinning/ No clearing

Simulations of dislocations gliding in Basal Plane

Edge type interaction, different Burgers vectors (bL=b3, bG=b2)

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 26

Simulations of dislocations gliding in Basal Plane

For basal slip: Dislocations are only pinned for 1/3 cases in the screw direction. Weak interaction or clearing for 2/3 cases in the screw direction. Clearing of loops is possible both in the edge and screw (and mixed) directions.

→ The expansion of the dislocation is possible in the screw direction, leading to an easier activation of basal slip than prismatic slip. → Possible clearing in the screw direction → easier formation of dislocation channels. → Furthermore, for one basal plane, the three slip systems can be activated, potentially leading to a full clearing of loops in the basal plane. → This explains the TEM observations of easier activation of basal slip after neutron irradiation and fully cleared channels in the basal plane.

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 27

A Multi-Scale Approach

TEM observations of grains →Deformation mechanisms Mechanical tests → Mechanical behavior

→ Need for a better understanding of the interactions between dislocation and loops to understand the observed deformation mechanisms

Dislocation Dynamics → Towards more complex and larger configurations In situ straining in TEM

• vs. Dislocation Dynamics

Molecular Dynamics → Details of dislocation–loop interactions

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 28

Zr +ion irradiation atJannus-Orsay (ARAMIS) Dose = 0.5 dpa (8. 1013 𝑗𝑝𝑜𝑡/𝑑𝑛2) Temperature= 500°C Energy= 0.6 MeV Zr

TEM foil

ions Zr+

20 nm

0.5 dpa à 500°C

In situ tensile test at Toulouse (CEMES) at temperatures between 350°C and 500°C.

In situ straining in TEM

ARAMIS facility at Jannus-Orsay (CSNSM)

Recrystallized Zy-4

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 29

Dislocation dynamics simulations vs. in situ TEM observations

Dislocation loop

B v  =

→ Evaluation of the friction coefficient Bp~0.3 MPa.s

Dislocation dynamics simulation of a real interaction observed in situ

From diffraction pattern indexing → Orientation of the grains vs. tensile axis From movie → Dimensions and positions of the dislocation and loop From curvature of the dislocation (DISDI software) → Evaluation of shear stress ~ 50 MPa → And applied tensile stress ~160 MPa From the kinetics → Evaluation of the velocity of the dislocation

Pyramidal plane

Tension

Burgers vector

x

7°

y z

<a> loop positions <a> dislocation in pyramidal plane Burgers vector

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 30

Dislocation dynamics simulations vs. in situ TEM observations

• Careful spatial and time scaling
• Systematic analysis of the effect of the loop nature, loop Burgers vector and position
• Careful comparison of the detailed shape of the dislocation

Drouet, J., Dupuy, L., Onimus, F., Mompiou, F. (2016). Scripta Materialia, 119, 71-75.

Bp=0.3 MPa.s BP=0.3 MPa.s BB=3 MPa.s Vacancy loop Same Burgers vectors

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 31 100 nm

Dislocation gliding in pyramidal plane (speed x2)

100 nm

𝑐

Dislocation dynamics simulations vs. in situ TEM observations The loop seems to be pinned by solute atoms

Bp=0.3 MPa.s BP=3 MPa.s BB=30 MPa.s Interstitial loop Same Burgers vectors

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 32

From Dislocation Dynamics → details of the interaction

Dislocation gliding in pyramidal plane at 350°C

Dislocation dynamics simulations vs. in situ TEM observations

Interstitial loop Different Burgers vectors

The loops seem to be pinned by solute atoms The dislocation seems to undergo dynamic strain ageing due to solute atoms

Bp=3 MPa.s BP=1 MPa.s BB=10 MPa.s

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 33

Conclusions 1/2

• <a>-loops act as pinning point to dislocation motion leading to radiation

induced hardening

• For sufficient applied stress <a>-loops can be cleared by gliding dislocations

leading to the formation of channels that are responsible for the early necking.

• Slip systems are not affected in the same way by irradiation: easier basal slip

activation and clearing of loops than for prismatic slip.

• DD simulations have been parametrized, with success, on MD simulations using

simple configurations

• DD simulations have been used to simulate more complex configurations
• Systematic simulations of many different geometries, for basal and prismatic

slip, have explained why basal activation and basal clearing is easier than prismatic slip.

• F. Onimus

19th International Symposium on Zirconium in the Nuclear Industry, 19–23 May 2019 | Manchester, UK 34

Conclusions 2/2

On good tracks towards a better understanding and a multi-scale modelling of the effects of irradiation on deformation mechanisms of zirconium alloys. In future prospects, this will help to improve the performance and safety of the nuclear fuel used in Light Water Reactors.

Thank you for your attention !

• In situ straining experiments in TEM have shown both the pinning of

dislocations by loops and the clearing of loops by gliding dislocations.

• In situ straining experiments have been correctly simulated by dislocation

dynamics confirming the extrapolation ability of this numerical tool.

• Towards quantitative analysis of the strength of dislocation - loop interaction
• Towards massive dislocation dynamics simulations involving many loops and

many dislocations.