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Cavity nucleation and growth during helium implantation and neutron irradiation of Fe
and steel
Eldrup, Morten Mostgaard; Singh, Bachu Narain
Publication date:
2012
Link to publication
Citation (APA):
Eldrup, M. M., & Singh, B. N. (2012). Cavity nucleation and growth during helium implantation and neutron
irradiation of Fe and steel. Poster session presented at 16th International Conference on Positron Annihilation
(ICPA-16), Bristol, United Kingdom.
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Cavity nucleation and growth during
helium implantation and neutron irradiation of Fe and steel
5
10
Fe
He implanted at 323 K
4
LOG COUNT
10
100 appm
10 appm
1 appm
Un-implanted
3
10
M. Eldrup and B.N. Singh
Department of Energy Conversion and Storage, Risø Campus, Technical University of Denmark, Denmark
2
10
360
1
10
0
1
2
3
340
4
IRON
300
323 K
PALS
260
240
d
e
t
n
a
l
mp
i
He
220
200
180
160
140
1 appm
120
100
280
10-4
260
10-2
10-3
623 K
220
10-1
The 323K-data for He-implanted (as well
as n-irradiated) specimens reflect the
presence of a high density of sub-nm
sized cavities, too small to be observed
by TEM.
m
pp
0a
10
180
160
140
100
At 623K a clear effect of He is observed.
This agrees with TEM observations.
100 appm He
+ n-irrad.
200
10-4
d
e
t
lan
p
im
e
H
10-3
10-2
n-irrad.
no He
10 appm He
+ n-irrad.
10-1
Total displacement dose (dpa)
Experimental Details:
(appm)
1, 10, 100
1, 10, 100
Neutron dose
He dose
rate
(appm/s)
(dpa)
6 10-4-1.2 10-2
0.001 – 0.1
1.2 10-3-1.2 10-2
0.1 – 0.3
Mean positron lifetime (ps)
140
100
Un-implanted
10-4
10-3
10-2
10-1
240
220
EUROFER 97
100 appm He
+ n-irrad.
623 K
200
No voids are observed by TEM after
neutron irradiation at 323K to the dose
levels used in the present experiments.
However, unexpectedly, large voids of
low density were observed if He was
implanted before irradiation with
neutrons.
Neutron irradiation at 623K (i.e. above
stage V) produces a fairly high density
of voids. If 100 ppm of He is implanted
before n-irradiation, the density of
cavities increases by a factor of ~7.
180
140
120
100
m
app
10
160
ted
n
a
l
p
m
i
e
H
n-irrad,
no He
This poster gives a brief overview of
a study of the microstructure, in
particular the cavity population, in
iron and Eurofer-97 after He
implantation and neutron irradiation.
Both He implantation and neutron
irradiation create populations of
cavities.
Un-implanted
10-4
10-3
10-2
TEM
10-1
Positron mean lifetimes for He implanted,
for neutron irradiated and for He implanted
plus neutron irradiated Eurofer-97 for
different displacement doses.
Timpl. = Tn-irr. = 323K or 623K
623K; 100 ppm He; n-irradiated 0.23 dpa.
Cavity size ~ 3.5 nm; density ~ 1022 m-3 .
Summary:
Like for Fe both n-irradiation and He
implantation lead to the agglomeration
of vacancies into small cavities both at
323K and at 623K as evidenced by the
increase of the positron mean lifetime
with displacement dose. However, the
effect is appreciably smaller than for
iron.
At 323K the presence of He does not
enhance cavity production by neutron
irradiation.
Probably - like for Fe – this is because
He bubbles constitute only a minor
fraction of the total cavity population.
At 623K post-implantation neutron
irradiation leads to a heterogeneous
population of cavities.
623K; n-irradiated 0.23 dpa. Void
size ~ 4.0 nm; density ~ 1.5 1021 m-3
TEM
At 623K, on the other hand, a clear
effect of He is observed.
Total displacement dose (dpa)
Thanks to: S.I. Golubov,
323K; 100 ppm He; n-irradiated 0.1 dpa.
Void size ~ 52 nm; density ~ 2 1019 m-3 .
Total displacement dose (dpa)
ppm
1a
PALS measurements were carried out on specimens that
were He implanted, neutron irradiated or neutron irradiated
after He implantation. Results are presented here in the form
of positron mean lifetimes.
A few of the specimens were also investigated by TEM.
100 appm He
+ n-irrad.
m
app
100
100 appm He gives rise to a displacement damage of
0.015dpa.
180
120
Mean positron lifetime (ps)
He dose
EUROFER-97
Timpl
= Tn-irr
(K)
~ 323 K
623 K
323 K
m
app
10
The He implantation and neutron irradiation parameters
were:
ppm
a
100
200
160
n-irrad, No He
EUROFER 97
ppm
1a
Specimens used for the experiments were pure iron and
Eurofer-97. They were He implanted uniformly at the Jülich
Compact Cyclotron. Subsequently many of the specimens
were neutron irradiated in the BR-2 reactor at Mol, Belgium.
220
Positron mean lifetimes for He implanted,
for neutron irradiated and for He implanted
plus neutron irradiated iron as functions of
displacement dose.
Timpl. = Tn-irr. = 323 K or 623 K.
200 nm
PALS
He
im
pla
nte
d
240
Both n-irradiation and He implantation
lead to the formation of cavities of
nanometer size both at 323K and at
623K as evidenced by the increase of
the positron mean lifetime with
displacement dose.
At 323K the presence of He does not
seem to enhance cavity production by
neutron irradiation.
Fe
240
120
10 appm He
+ n-irrad.
annealed
m
app
10
Mean positron lifetime (ps)
100 appm He
+ n-irrad.
d
e
t
ia
d
rra
i
n
280
ppm
1a
In order to investigate the role of He in cavity
nucleation in neutron irradiated iron and steel,
pure iron and Eurofer-97 steel have been He
implanted and neutron irradiated in a
systematic way at different temperatures, to
different He and neutron doses and with
different He implantation rates.
The defect microstructure, in particular the
cavities, was characterized using Positron
Annihilation Lifetime Spectroscopy (PALS)
and Transmission Electron Microscopy
(TEM).
Fe
m
pp
0a
10
Introduction:
320
pm
ap
10
Mean positron lifetime (ps)
TIME (nsec)
623K; 100 ppm He; n-irradiated 0.23 dpa.
Very inhomogeneous cavity distribution.
Cavities seem to form only at dislocations
and interfaces, except for a very low
density of large voids.
At 323K pre-implantation of He only
influences the effect of neutron
irradiation to a small extent..
At 623K on the other hand, He
strongly enhances the density of
cavities after neutron irradiation.