Photon Factory Activity Report 2017 #35 (2018)

BL-27B/2016G037

EXAFS study on irradiation-induced hardening of Fe ternary alloys
Akihiro IWASE1,*, Takara SUMIE1, Fuminobu HORI1, Yuichi SAITOH2, Satoshi SEMBOSHI3, andYoshihiro OKAMOTO4
1
Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan
2
National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma,370-1292, Japan
3 Institute for Materials Research, Tohoku University, Sendai, Miyagi, 980-8577, Japan
4
Japan Atomic Energy Agency, Sayo, Hyogo, 679-5148, Japan
1 Introduction
Hardening and embrittlement by the irradiation
become a serious problem for nuclear reactor pressure
vessel steels which have been exposed to high flux
energetic neutrons for a long period. In the previous
study, we have used Fe-0.6wt.%Cu binary alloy samples
as a model alloy for the reactor pressure vessel alloys, andhave shown that the precipitation of Cu atoms induced byenergetic electron irradiation causes the hardening of thesamples [1,2]. In the present report, we will show theresult of the heavy ion irradiation on the hardness andatomic arrangement of Fe-Cu-Mn and Fe-Cu-Ni ternary
alloys through the Vickers hardness and the EXAFS
spectrum measurements.
2 Experiment
We prepared samples of homogeneous Fe-0.6wt.%
Cu-1.5wt.%Mn alloy and Fe-0.6wt.%Cu-1.5wt.%Ni alloyby the thermal treatment at 800C. Such samples wereirradiated with 16eV Au ions at 523K by using a tandem
accelerator of QST-Takasaki. The Au ion fluences were
3x1014/cm2 and 3x1015/cm2. The change in hardness by
the irradiation was measured by means of the Vickers
hardness tester. To observe the local structures near Cu,
Mn or Ni atoms in Fe matrix, the EXAFS spectra wereobtained around the Cu-K, Mn-K and Ni-K absorption
edges by using the KEK photon factory.
3 Results and Discussion
Figs. 1and 2 show the EXAFS-FT spectra for Fe-0.6wt.%
Cu-1.5wt.%Mn alloy irradiated with 16MeV Au ionsnear Cu-K absorption edge and Mn-K absorption edge,
respectively. In the figures, the spectra for the irradiatedsurface (red curves) and those for the unirradiated surface(blue curves) are compared. The shapes of the EXAFS
spectra for the both surfaces show the BCC structure. The
result means that Mn and Cu atoms occupy the regular
BCC sites of Fe matrix before and even after theirradiation. The ion irradiation decreases the spectrum
intensity. The decrease in the spectrum intensity by theirradiation is much more remarkable for the Cu-K edge
than for Mn-K edge. Figs. 3 and 4 show the EXAFS-FT
spectra for Fe-0.6wt.% Cu-1.5wt.%Ni alloy irradiatedwith 16MeV Au ions near Cu-K absorption edge and Ni-FTR (A)Fig.1 EXAFS-FT spectra around Cu-K absorption edge
for Fe-0.6wt.%Cu-1.5wt% Mn alloy. Blue line: forunirradiated surface, and red line: for irradiated surface.
Irradiation fluence is 3x1015/cm2.

FTR(A)
Fig.2 EXAFS-FT spectra around Mn-K absorption edge
for Fe-0.6wt.%Cu-1.5wt% Mn alloy. Blue line: forunirradiated surface, and red line: for irradiated surface.
Irradiation fluence is 3x1015/cm2.

Photon Factory Activity Report 2017 #35 (2018)

growth of small clusters in Fe matrix. Such Cu and Niclusters act as effective obstacles against the dislocation
motion, and cause the hardening of the alloys. As can beseen in Figs. 5 and 6, the Vickers hardness surely
increases by the Au ion irradiation for the both alloys.

FTR (A)

Hv

240

200

Fig.3 EXAFS-FT spectra around Cu-K absorption edge
for Fe-0.6wt.%Cu-1.5wt% Ni alloy. Blue line: forunirradiated surface, and red line: for irradiated surface.
Irradiation fluence is 3x1015/cm2.

160

3x10143x1015Ion fluence (cm-2)

0Fig.5 Vickers hardness as a function of Au ion fluence forFe-0.6wt.%Cu-1.5wt%Mn alloy.

FTHv

240

200R (A)160

Fig.4 EXAFS-FT spectra around Ni-K absorption edge
for Fe-0.6wt.%Cu-1.5wt% Ni alloy. Blue line: forunirradiated surface, and red line: for irradiated surface.
Irradiation fluence is 3x1015/cm2.
K absorption edge, respectively. The decrease inspectrum intensity is observed by the irradiation, and thedecrease in spectrum intensity is about the same for Cu-K
edge and Ni-K edge. Generally, the disordering of atomic
arrangements (the increase in Debye Waller factor) and/or
the decrease in coordination number of neighbour atoms
cause the decrease in EXAFS intensity. In the presentcase, the spectrum decrease by the irradiation can be
explained as due to the segregation of Cu, Ni and/or Mn
atoms around Cu and Ni atoms, which causes the increasein the Debye Waller factor. As the decrease in EXAFS
spectrum intensity for Mn-K edge is quite small, thesegregation of added elements around Mn atoms scarcely
occurs during the irradiation. The segregation around theadded Cu and Ni elements leads to the nucleation and the03x1014
Ion fluence (cm-2)

3x1015

Fig.6 Vickers hardness as a function of Au ion fluence forFe-0.6wt.%Cu-1.5wt%Ni alloy.
References[1] T. Tobita et al., J. Nucl. Mater. 452(2014) 241-247.
[2] Y. Fujimura et al., Nucl. Instr. Meth. B354(2015)
120-124.
Acknowledgement
The authors thank the technical staff of QST-Takasaki
accelerators and KEK-PF for their help.

* iwase@mtr.osakafu-u.ac.jp