Micromechanical testing of nuclear materials...damage profile. • 0.26 dpa –300 C and 750 C •...
Transcript of Micromechanical testing of nuclear materials...damage profile. • 0.26 dpa –300 C and 750 C •...
Advanced micromechanical testing
techniques of irradiated materials for
Nuclear applications
Dr Anna Kareer
Department of Materials, University of Oxford
RaDIATE Collaboration Meeting, Geneva, 17-21 December 2018
Radiation damage threats to structural
materials
1) Reduction in ductility and
work hardening capabilities
2) Segregation/precipitation
leading to embrittlement
3) Plastic instability and
prompt necking after yield
Microstrucuture
of neutron
irradiated Fe-
9Cr15 cm
Typical uniaxial tensile behaviour of
structural steels after irradiation
18/12/2018 A,Kareer | RaDIATE collaboration meeting 2018
Current reactor
maximum operating
conditions
Overview of operating temperatures and
expected damage levels for Generation IV
reactor designs.
Estimated operating temperature windows for
various structural materials in nuclear systems
with damage levels of 10-50 dpa.
Zinkle, S. J. & Busby, J. T. Structural materials for fission & fusion energy
Structural materials represent the key for containment of nuclear fuel. Mater.
Today 12, 12–19 (2009).
Materials issues in Future reactors
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Mechanical testing of reactor irradiated
materials
Advanced test reactor (ATR)
Idaho national laboratory
Culham Materials Research Facility
(MRF) – Hot cell facility
• Low dose rates (200 dpa of damage in a test reactor would
take decades to achieve)
• Radioactive material handling / specialist facilities required for
active material
• Not efficient process for rapid characterisation of
mechanical response (expensive and time consuming)
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• Much higher dose rates (104 that
of reactor irradiation)
• Negligible levels of activity
• Relatively cheap
• However only small volumes of
damaged material obtained…0
10
20
30
40
0
2
4
6
8
10
0 500 1000 1500 2000
Dis
pla
cem
ents
per
ato
m (
dp
a) H
elium
Co
ncen
tratio
n (ap
pm
)
Depth (nm)
Damage
Helium
Need for small scale mechanical testing to predict bulk properties
Mechanical testing of heavy ion irradiated
material
H + and Fe +
• Use ion irradiation to simulate neutron damage
420oC
5MeV
Ion irradiated damaged
microstructure
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Nanoindentation: surface indentation vs.
cross-sectional indentation
Kiener, Daniel, et al. "Application of small-scale testing for investigation of ion-beam-
irradiated materials." Journal of Materials Research 27.21 (2012): 2724-2736.
• Measure hardness/yield strength and modulus
• Measure the relative increase in hardness due to
irradiation damage
• Plastic zone extends into regions of unirradiated
martial
• Indentation size effects for small indentation depth
Surface indentation
Cross-sectional
indentation
𝐻 = 3𝜎𝑦
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Nanoindentation of Fe++ irradiated candidate
steels: Surface indentation
• Measure hardness/yield strength and
modulus as a function of depth –
dynamic indentation mode
• Measurement affected by the
indentation depth → Indentation size
effect unless large damaged layer02468
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0 5 10
DP
A
Depth / um
High energy 70MeV Fe++
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Bulk σy = 630MPa
10µm
Nanoindentation of Fe++ irradiated candidate
steels: Cross-section indentation
02468
10121416182022
0 2 4 6 8 10
DP
A
Depth / um
70MeV Fe++
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High temperature Nanoindentation
• Variable temperature indenter (-
100~950 °C)
• Heats indenter tip and sample separately
allow isothermal contact
• High vacuum - prevents oxidation (10-7
mbar)
• Extremely low thermal drift even at high
temperature
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High temperature Nanoindentation: He+
implanted Tungsten – Fusion applications
JSKL Gibson, SG Roberts, DEJ Armstrong MSEA 625, 380-384
To simulate damage in fusion
divertor helium ions
implanted into pure tungsten
at 850oC
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Spherical indentation/macroscopic
compression in T91
5 µm
5 µm10 µm
20 µm
0 0.05 0.1 0.15 0.2
Strain
0
0.5
1
1.5
2
2.5
3
3.5
4
Str
ess
/ G
Pa
20um indenter
10 um indenter
5um indenter
Macroscopic compression
Hertzian contact
E = 210 GPa
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Microcantilver testing of ODS steel: Stress
strain behaviour
Load
4 µm
• FIB machined micro-cantilevers in ODS and non ODS
• 20 x 4 x 5 micron with triangular cross section
• 0 dpa or 0.026 dpa Surrey at beam centre
• Stress-strain behaviour calculated using FEA model to
account for non-fixed end
C. Jones, D.E.J.Armstrong. S.G. Roberts18/12/2018 A,Kareer | RaDIATE collaboration meeting 2018
Macroscopic mechanical behaviour: ODS
steels
4 µm
C. Jones, D.E.J.Armstrong. S.G. Roberts
• Samples 1x1x12mm
• Samples tested in 4-
point bending
• Strain calculated using
digital image
correlation (DIC).
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Macroscopic mechanical behaviour: ODS steels
4 µm
C. Jones, D.E.J.Armstrong. S.G. Roberts
MaterialAverage elastic
modulus /GPa
Average yield
stress /MPa
Non ODS 281 ± 6 421 + 35− 32
ODS 299 ± 6 842 + 63− 47
No oxide
particles
Oxide
Particles
15um
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Microcantilever bend testing of proton
irradiated ODS steels
4 µm
ODSNon-ODS
Non - ODS ODS
Modulus / GPa Yield Stress/ GPa Modulus / GPa Yield stress/ GPa
Unirradiated 208±5 1.05±0.07 216±20 1.30±0.4
Irradiated 224±6 1.57±0.15 196±12 1.44±0.3
C. Jones, D.E.J.Armstrong. S.G. Roberts
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Cantilever depth (μm)
Yie
ld S
tres
s (G
Pa
)
Bulk yield stress non
oxide containing
Bulk yield stress oxide
containing
Size effect observed,
Minimal effect above 5μm
thickness
Microcantilever bend testing of proton
irradiated ODS steels: Size effects
C. Jones, D.E.J.Armstrong. S.G. Roberts
18/12/2018 A,Kareer | RaDIATE collaboration meeting 2018
Microcantilever bend testing of proton
irradiated structural steels: Size effects
4 µm
The apparent
strength of the
microcantilevers
appeared to
drastically deviate
from macroscale
values (i.e. source
limited) for beam
depths ≤ 4.5 µm
C. Jones, D.E.J.Armstrong. S.G. Roberts
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0.0 0.5 1.0 1.5 2.00.0
0.5
1.0
1.5
Fracture
Lo
ad
, m
NBending displacement, m
• Si ions.
• Three energies 500 keV, 1 MeV, 2 MeV.
• Damaged zone ~1.4 µm deep.
• Dose ratio 3 : 2 : 1 relatively uniform damage profile.
• 0.26 dpa – 300°C and 750°C
• Microcantilevers manufactured in the interphase, fibre and matrix of both irradiated and unirradiated material
Ion irradiation of SiC-SiC composites for
nuclear applications – fracture experiments
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Dam
age level, a
.u.
Depth, m
Fiber
5 µm
Interphase
5 µm5 µm
Matrix
2 µm
Damage profile
500 nm
Dr Y. Zayachuk18/12/2018 A,Kareer | RaDIATE collaboration meeting 2018
Ion irradiation of SiC-SiC composites for
nuclear applications – fracture experiments
Dr Y. Zayachuk
0
1
2
3
4
5
Matrix
Fiber
Fra
ctu
re toughness, M
Pa*m
1/2
Interphase
0
1
2
3
4
5
6Single-layered interphase
Unirradiated
0.26 dpa, 300oC
2.6 dpa, 750oC
Fra
ctu
re t
ou
gh
ne
ss, M
Pa
*m1/2
Interphase
Fiber
Matrix
Unirradiated Irradiated
Following the irradiations:
Interphase – toughness increases, doesn’t
noticeably change with the increase of
dose.
Fiber – toughness progressively increases
with the increase of dose.
Matrix – no clear trend.
Fracture toughness measurements –
cantilevers with straight notch.
Matrix – 4.1 MPa*m1/2
Fiber – 2.1 MPa*m1/2
Interphase – 0.8 MPa*m1/2.
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Ion irradiation of SiC-SiC composites for
nuclear applications – fracture behaviour at
temperature
Dr Y. Zayachuk
0.02 0.04 0.06 0.08 0.10 0.12 0.140
5
10
15
20
25
30
600oC
RT
Fra
ctu
re s
tre
ss, G
Pa
Fracture strain
Single-layered interphase grade
Cantilevers in the matrix
• Room temperature:
Fracture stress – 21 GPa;
Fracture strain – 13%.
• 600°C:
Fracture stress – 12 GPa;
Fracture strain – 5%.
Hot nanoindenter (Micro Materials
NanoTest Xtreme) – vacuum tests at
600°C .
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Microcantilever fracture experiments: load –
unload in Tungsten
2 um
load partial-unload
chevron notch
stable crack growth & plasticity- softening of the LD curve
- displacement jumps
loading/unloading rate: 5 μN/s
B. Li, D.E.J.Armstrong, S.G.Roberts18/12/2018 A,Kareer | RaDIATE collaboration meeting 2018
Microcantilever fracture experiments:
Tungsten: Post-mortem fractography
B. Li, D.E.J.Armstrong, S.G.Roberts
2 um
22/06/16400 nm
Stable crack growth
Cleavage fracture surface
Curved crack front
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Dislocation based CPFEM to simulate
Nanoindentation in implanted Tungsten
S. Das, F. Hoffmann, E.K.Tarleton
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Summary
• By simulating reactor irradiation with charged particle accelerators –
provide rabid screening of radiation damage in candidate materials for
nuclear applications
• Micromechanical testing enables a large amount of data to be obtained
from small volumes of material (either active material or where only
small volumes are available or shallow irradiated layers)
• Nanoindentation is a rapid screening tool to measure the
hardness/modulus of irradiated material, microcantilevers can be used to
obtain mechanical properties beyond the yield point (full flow curve) and
fracture behaviour
• Combining micromechanical tests with dislocation based modelling
enables a full characterisation of the mechanical properties of irradiated
materials
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Thank you!