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Effect of Temperature Change on Irradiation
Hardening of Ferritic and Austenitic Steels during
Ion-irradiation
S. Jitsukawa a) , M. Ando b) , I. Ioka a) , Y. Abe a) , T. Onitsuka a, c) , N. Ishikawa a) and N. Okubo a)
a) Division of Fuels and Materials Engineering, NSED,
b) Division of Fusion Reactor Engineering, FRDD, c) NSRC, JAEA
It has been reported that change of irradiation condition (e.g.
irradiation temperature and damage rate) affects microstructural
and property changes of metals and alloys 1) . It may accelerate
irradiation hardening to reduce residual ductility leading
quasi-brittle fracture. Effect of temperature change on the
irradiation hardening is examined.
An 8Cr-2W (0.1C-8Cr-2W-VTa) reduced activation ferritic
steel F82H (developed by JAEA and JFE corporation), F82H
doped with 1wt%-Ni (F82H+1Ni) and a type 316 stainless steel
316F (0.04C-0.04Si-17Cr-14Ni-2Mo) were used. Both F82H
and F82H+1Ni were normalized at 1313 K. This was
followed by tempering at 1023 K for 1.5 h. 316F was used
after solution annealing at 1323 K for 1 h. Plates of the alloys
were cut into those of 3 mm × 6 mm × 0.75 mm in size, and
irradiation was conducted on the rectangular surfaces of 6 mm
× 0.75 mm at temperatures of 523 K to 653 K with 10.5 MeV
Fe 3+ ions as well as He and H ions. Average damage rate was
1.0E-3 dpa/s at a depth of 1 m; the projected range for Fe 3+
ions was of about 2 m.
Two accumulated damage levels of 9 dpa (displacement of
atom) and 20 dpa were selected. For 9 dpa specimens,
irradiation temperatures of 573 K and 648 K were applied.
Also, temperature was changed for some of the specimens
between these temperatures during irradiation. For 20 dpa
specimens, 523 K and 653 K were applied. Temperature was
changed between these two temperatures for some of the
specimens. Temperature changes were performed at every
3 dpa, as seen in Fig. 1. The number of temperature changes
were 3 and 6 for 9 dpa and 20 dpa specimens, respectively.
Ultra-micro hardness testing was conducted after irradiation
at the ion-incident surfaces. Penetration depth of 1 m was
kept for all the tests to minimize the effect of the depth
distribution of the irradiation damage. The Ultra-microhardness
testing machine of EMT-1100a (Elionics) was used
for the tests.
Hardness values after irradiation was shown in Fig. 2. The
figure indicates the increment of hardness during irradiation.
Both temperature dependence and damage level dependence of
hardening for 316F was relatively small, although it exhibited
hardening by 1.5 GPa. F82H specimens irradiated at
temperatures cyclically changed exhibited maximal hardening.
The response of F82H+1Ni specimens was rather complicated.
Hardening attained maximal after 20 dpa by temperature change,
while it was smaller than the others at 9 dpa.
Temperature dependence of hardness after irradiation to
10 dpa for F82H was plotted in Fig. 3. Figure indicates that
irradiation hardening attained maximal after irradiation to
10 dpa at temperatures of 673 K. It was also indicated that
hardening by ion-irradiation tends to exhibit maximal at
temperatures of between 623 K and 673 K for these steels 4) .
These suggest that temperature change enhanced irradiation
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hardening. It has been also reported that temperature change
during irradiation caused acceleration of irradiation induced
1- 5)
microstructural change and hardening . Several authors
have reported that the effects decreased with damage levels.
Results in Fig. 2, however, indicated different tendencies.
Irradiation hardening often reduces residual ductility and
fracture toughness of the materials. Results by fission reactor
irradiation experiments indicate that residual ductility is not
small and the margin to ductile fracture remains to be
reasonable level even after irradiation to some tens of dpas at
6, 7)
temperatures where irradiation hardening occurs . However,
it should be noted that residual capability of work hardening is
also rather limited and the additional hardening may reduce
residual ductility to a considerable degree.
Fig. 1 Pattern of the
temperature change.
Temperature was
reduced every 3 dpa
and recovered.
573 573-648 648K 523 523-653 653K
Fig. 2 Hardening at constant and cyclically changed temperature.
Fig. 3 Temperature
dependence of
hardening at 10
dpa.
References
1) Y. Yoshida et al., J. Nucl. Mater. 212-215 (1994) 471-475.
2) S. Jitsukawa et al., J. Nucl. Mater. 307-311 (2002) 179-186.
3) S. Jitsukawa et al., J. Nucl. Mater. 329-333 (2004) 39-46.
4) M. Ando, private communication.
5) S. Jitsukawa et al., J. Nucl. Mater. 367-370 (2007) 539-543.
6) K. Suzuki et al., Nucl. Eng. Design 240 (2010) 1290-1305.
7) S. Jitsukawa et. al., Nuclear Fusion 49 (2009) 115006.