Residual Stress Characterization In Zirconium Oxides Using

Synchrotron XRD

Manchester Materials Science Centre, The University of Manchester, Grosvenor Street , Manchester M1 7HS, United Kingdom

Efthymios Polatidis, Philipp Frankel, Jianfei Wei, Michael Preuss

Uses and corrosion of Zr-Alloys

Zr-alloys used as cladding materials of the fuel rods.

In service environments oxidation occurs limiting their service life.

OXIDE

METAL

Uses and corrosion of Zr-Alloys

Zr-alloys used as cladding materials of the fuel rods.

In service environments oxidation occurs limiting their service life.

Better understanding of the corrosion mechanisms could lead to improvement of the burn up efficiency.

Residual stresses in the oxide are believed to play key role on the corrosion properties of the material.

Origin of stressesTransformation strain. Transformation of Zr-ZrO2 is accompanied by volume dilatation. (volume of ZrO2 is 1.56 times greater than Zr)

How do stresses affect oxidation?• The tetragonal phase can be stress stabilised

• As oxidation proceeds stresses might be reduced in the oxide away from the interface, which could lead to t m phase transformation

• This phase transformation is associated with a further volume increase ─ cracks─ acceleration of corrosion kinetics

Stresses in Zr-alloys oxides

Synchrotron X-Ray diffraction experiment at BESSY EDDI, Berlin

Residual strain (along the oxide thickness) can be extracted by altering the incident angle theta. Sin2psi method.

Fixed angle

detector

Sample

Diffracted beam Incoming white beampsi

θ

m(-

111)

t(10

1)

Zr(

100)

m(0

02)

Zr(

002)

Zr(

101)

m(-

211)

m(2

11)

Zr(

102)

m(-

122)

m(2

21)

Zr(

103)

Synchrotron X-Ray diffraction experiment at BESSY EDDI, Berlin

Increasing penetration

Higher energy - greater penetration - depth profile

Diffraction spectrum for each measurement angle ψ

Lowest angle= highest energy

Max. Pen. greater than oxide thickness

Highest angle= lowest energy

Max. Pen. Only samples part of oxide thickness

≈

θ θθ

metal metal metal

Penetration depth with 2θ

Results

ZIRLO™ SR/80 days at 360°C ZIRLO™ SR/160 days at 360°C

Maximum stress - close to the O/M interface

Oxide Metal Oxide Metal

Distance from outer surface (um) Distance from outer surface (um)

Res

idua

l Str

ess

(MPa

)

Res

idua

l Str

ess

(MPa

)

Synchrotron XRD experiment at ESRF ID11, France

Using XRD diffraction in transmission geometry and monochromatic beam, the setup allows strain characterization along the oxide thickness:

DetectorSample

Diffracted cones

Incoming beam

Residual strain (along the oxide thickness) can be extracted by comparing “strain free” samples with strained lattice spacing values.

(dstrained-dstrain free )/dstrained = strain

y

z

oxide 85º95º

5º

-5º

For each measurement point

Diffraction Pattern

Synchrotron XRD experiment at ESRF ID11, France

For each measurement point

Diffraction pattern85º95º

5º

-5º

Diffraction spectrum

Synchrotron XRD experiment at ESRF ID11, France

Stress calculation

• Strain= (dhkl-d0)/d0

• Extract stress tensor using Hooke’s Law, knowing in plane (εxx) and out of plane

(εyy) strain.

x

y

oxide

Metal

z

FE analysis suggests that the out of plane stress (σyy) is equal to zero, thus out of plane strain (εyy) occurs due to Poisson’s contraction.

Results

Compressive stresses - Oxide

Balancing tensile stresses-Metal- High temperature/time-Creep

FEM simulating the stress due to oxide volume expansion and relaxation due to

creep

High TTensionHigh T

compression

Relaxed TensionHigh T

Relaxed compression

TensionHigh T

compression

Relaxed TensionHigh T

Relaxed compressionRelaxed compression

compression

Creep of the substrate

Measured Elongation by creep (M. Blat‐Yrieix et. al)FEM creep strain

Evolution of strain versus oxide thickness

Creep of the substrate

Blat-Yrieix M. et. al, Toward a Better Understanding of Dimensional Changes in Zircaloy-4: What is the Impact Induced by Hydrides and Oxide Layer?, Journal of ASTM International, Vol. 5, No. 9, 2008.

Distance from O/M interface (μm)

Creep of the substrate

Conclusions

• A stress profile exists through oxide thickness - maximum compressive

stresses near the O/M interface stress decay away from interface may enable

tetragonal to monoclinic phase transformation.

• Stress reduces with oxidation time.

• A stress profile may be produced by creep of substrate – however

the shape of the measured profile does not match the profiles predicted by

substrate creep alone.

• Stress profile affected by other factors such as cracks between the oxide

layers.

Thank you!