Photon Factory Activity Report 2014 #32 (2015) B

BL-27B/2013G616

EXAFS study on Fe precipitates in CuFe alloys
induced by thermal aging and plastic deformation
Yuki Fujimura1, Satoshi Semboshi2, Yoshihiro Okamoto3, and Akihiro Iwase1＊
Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
2
Institute of Materials Research, Tohoku University, Sakai, Osaka 599-8531, Japan
3
Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
1

2 Experiment
We prepared specimens of supersaturated Cu-1at.%Fealloy by the following methods. Starting raw materials
were pure Cu and pure Fe the atomic ratio of which was
99 : 1. They were melted by the high frequency induction
melting method. The resulting ingots were cold-rolled
into sheets about 1 mm thick. As a solution-treatment, thesheets were annealed at 1273 K for 1 hour, and they werequenched into iced-water. This solution treatment ensured
a homogeneous distribution of Fe atoms in Cu matrix.
So l u tio n - trea ted sp ec i m en s we r e t her ma l l yag ed at 8 7 3 K fo r var i o u s ti me i n ter va l s ( 1 1 2 0 ho urs ) i n ar go n at mo sp h er e. After thethermal-aging, we performed the micro Vickers hardness
measurements at room temperature. The hardness for thesolution-treated specimen was also measured. The applied
load for the Vickers hardness measurement was 100 gf.
The magnetic properties for the solution-treatedspecimens and the thermally aged specimens wereinvestigated by using a SQUID magnetometer. In thismeasurement, the applied magnetic field was -5 T to 5T,and the measurements were performed at 300K.
To observe the local structures around Fe atoms in Cu
matrix of the CuFe specimens, we performed the EXAFS
measurements around the Fe K absorption edge (7.11keV) at the 27B beamline of the synchrotron radiation
facility of High Energy Accelerator Research
Organization (KEK-PF). The EXAFS spectra wereobtained using a 7 element germanium detector by thefluorescence method at room temperature. As a referencedata, the EXAFS spectrum for a pure Fe foil 5 μm thick
was obtained by the transmission method. We used thecomputer software, WinXas[2] for analyzing the obtained

EXAFS spectra. In the analysis, all EXAFS spectra wereFourier transformed using k3 weighting with the k range
from 2 - 3 to 11 - 15 Å-1. Besides, EXAFS simulations
were performed using the computer code, FEFF [3]. The
simulation was calculated for the state of Fe such as thecase of an Fe atom surrounded by Cu fcc lattice for the 1 5th nearest neighbor Cu atoms of an Fe atom.
Some thermally aged specimens and solution treatedspecimen were cold-rolled at the reduction of 70 %, andinvestigated the effect of the deformation by using aSQUID magnetometer and EXAFS measurements.
3 Results and Discussion
Fig. 1 shows the Vickers hardness change for the Cu1at.%Fe themally aged at 873 K as a function of aging
time. The Vickers hardness increases, and reaches amaximum value after 30 hour-aging, and then decreases
with increasing the aging time. The age-hardnening curve
was considered as due to the appearance of Fe
presipitations and their growth in the specimen.

Change in Vickers Hardness (HV)

1 Introduction
The extended X-ray absorption fine structure (EXAFS)
measurement is a useful tool for the observation of local
atomic arrangements around selected atoms. In ourprevious study [1], we have observed the local structurearound Fe atoms in Cu-3at.%Fe alloys and investigated
the relationship between micro structure around Fe atoms
in Cu matrix and hardness by using EXAFS
measurements and Vickers hardness measurements. In
addition to these results, in this report, we haveinvestigated the effects of Fe precipitations on magnetic
properties, and deformation, and then studied therelationship between change in these properties and micro
structure around Fe atoms, by means of EXAFS
measurements.

3020100020406080100120

Aging Time (hrs.)
Fig. 1 Vickers hardness change for the Cu-1at.%Fethemally aged at 873 K as a function of aging time.

Photon Factory Activity Report 2014 #32 (2015) B

mainly have the fcc structure as a result of coherent
growth in fcc Cu matrix. Therefore, the results of thehardness and the EXAFS measurements indicate that Fe
precipitates with the fcc structure were produced. On theother hand, the shape of the experimental FT spectra forthe specimen thermally aged at 873 K for 72 or 120 hours
are similar to that for the pure Fe foil. This result suggeststhat the structure of Fe precipitates gradually changes
from the fcc structure to the intrinsic bcc structure withincreasing the thermal aging time and therefore with thegrowth of Fe precipitates.

r1,r2
r4,r5
r3Pure Fe

120hrsMagnetization ( emu/g )86

Fe|FT| (a.u.)

72hrs

30hrs

5hrs

420-2
5hrs
30hrs
72hrs
120hrs-4-6

R1Solution treated
R2 R3 R4-812 3 4 5 6 7
Radial Coordinate(Å)-4-202446

Magnetic field ( ×10 Oe )FEFF-simulation

0-6Fig. 3 Magnetization for the thermally aged specimens at873 K as a function of magnetic field.
8Fig. 2 FT EXAFS spectra near Fe K absorption edge forthe specimens thermally aged at 873 K. For comparison,
the spectra for the solution-treated specimen, the pure Fe
foil, and the simulated one by using FEFF code are alsoshown.
Fig. 2 shows the Fourier transformed (FT) EXAFSspectra near Fe K absorption edge for the specimens
which were thermally aged at 873K. For comparison, thespectra for the solution-treated specimen, the pure Fe foil,
and the simulated one by using FEFF code are also shown.
The shape of the experimental FT EXAFS spectrum forthe solution-treated specimen is similar to the simulation
spectrum by using FEFF code. This result implies that Featoms are well dispersed in Cu matrix, and each Fe atom
is surrounded by Cu atoms with the fcc structure. The
shape of the experimental FT spectra for the specimens
thermally aged at 873 K for 5 or 30 hours are also similar
to the simulation spectrum by using FEFF code. However,as can be seen in Fig. 1, in the beginning of Fe
precipitations for CuFe specimens, the Fe precipitates

Then, we discuss the change in magnetization induced bythermal-aging. Since magnetic Fe atoms were
homogeneously distributed in non-magnetic Cu matrix,
the solution treated specimen shows the paramagnetism.
Fig. 3 shows the magnetization for the thermally aged
specimens as a function of magnetic field at 300K. All thethermally aged specimens show the ferromagnetism. The
magnetization for the thermally aged specimens isincreased with increasing the aging time. Since theamount of ferromagnetic Fe precipitates which have bcc
structure were increased with increasing the aging time,
the shapes of FT-EXAFS spectra for the sufficiently
longtime-aged specimens which were aged for 72, 120
hours were similar to that for pure Fe foil (Fig. 2).
In order to investigate the effects of deformation onmagnetic properties and the atomic structures of Fe
precipitates, the 30 hour-aged specimen and solutiontreated specimen were cold-rolled by the reduction of
70 %. Fig. 4 shows the FT-EXAFS spectra for thespecimens which were cold-rolled after 30 hour-aging or
after solution-treatment. For comparison, the spectra forthe solution-treated specimen, and the pure Fe foil, arealso shown. As mentioned above, in the 30 hour-aged

Photon Factory Activity Report 2014 #32 (2015) B

r1,r2
r4,r5
r3

Pure Fe| FT | (a.u.)

cold-rolled
after 30 hrs-aging

rolled specimen after 30 hour-aging has a hugemagnetization. This experimental result can be explained
as follows. Since a large amount of non-magnetic Fe
precipitates with fcc structure were transformed to bcc
structure by the deformation (the cold-rolling), themagnetization was greatly increased. This result confirms
the EXAFS result which is shown in Fig.4.
100Fe

Magnetization ( emu/g )specimen, Fe precipitates were produced by thermalaging, and have mainly fcc structure. On the other hand,the shape of the FT-EXAFS spectrum for the specimen
which was cold-rolled after 30 hour-aging was similar tothat for the pure Fe foil. Furthermore, the FT-EXFAS
spectrum for the solution-treated specimen was hardlychanged by cold rolling. These results imply that Fe
precipitates in the 30 hour-aged specimen which had
mainly fcc structure, were transformed from fcc structure
to intrinsic bcc structure by the deformation (cold-rolling).
The shape of FT-EXAFS spectrum for the cold-rolled
specimen after solution-treatment, whose Fe atoms werehomogeniously distributed in the Cu fcc matrix, washardly changed from that for solution-treated one.

500-5030hrs
30hrs,rolled-100-6-4-2

02

446

Magnetic field ( ×10 Oe )Fig. 5 Magnetization-magnetic field curves as for thespecimen which was only thermally aged for 30 hours at
873 K and for the specimen which was cold-rolled after
30 hour-aging at 873 K.

30hrs
cold-rolled
after solution-treatedR1

solution treated
R2R3 R4

0 1 2 3 4 5 6 7 8
Radial Coordinate(Å)
Fig. 4 FT EXAFS spectra near Fe K absorption edge forthe specimens thermally aged at 873 K, and cold-rolled
ones. For comparison, the spectra for the solution-treatedspecimen, and the pure Fe foil, are also shown.
After cold-rolling, the magnetization for solution-treatedspecimen was not changed from that one before coldrolling. Fig. 5 shows the magnetization for the specimen
which was thermally aged for 30 hours and the coldrolled one after 30 hour-aging as a function of magnetic
field at 300K. Since there were a large amount of nonmagnetic Fe precipitates with fcc structure, themagnetization for the specimen which was thermally agedfor 30 hours were very small. On the other hand, the cold-References[1] Y. Fujimura at.al. Photon Factory Activity Report2013 #31 (2014) B[2] T.Ressler, J.Synchrotron Rad. 5 (1998) 118[3] S.I. Zabinsky, J.J. Rehr, A.Ankunidov, R.C. Albers,
M.J. Eller, Phys. Rev. B 52 (1995) 2995

* iwase@mtr.osakafu-u ac.jp