Photon Factory Activity Report 2014 #32 (2015) B
BL-27B/2013G616

Effect of Energetic Ion Irradiation on Lattice Structure and Mechanical Properties ofNi3Nb Intermetallic compound
Hiroshi Kojima1, Yuki Fujimura1, Hiroaki Yosizaki1, Yasuyuki Kaneno1 ,Yoshihiro Okamoto2, Yuichi Saitoh3, and Akihiro Iwase1
1Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
2
Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan3
Department of Advanced Radiation Technology, Japan Atomic Energy Agency, Takasaki, Gunma,370-1292, Japan1Introduction
Energetic ion irradiation locally gives high density
energy deposition into a target, and it can induce
non-thermal equilibrium phases. In our previous results,
we showed the ion irradiation induced phase transition for
Ni3V and Ni3Al intermetallic compounds1), 2). Ni3V shows
the tetragonal ordered structure (D022 structure) at room
temperature before the irradiation. After the ionirradiation, it transforms to the cubic disordered structure
which is usually found in the thermal equilibrium phase
diagram at high temperatures. On the other hand, theunirradiated Ni3Al shows the cubic ordered structure( L12 structure) and this structure is retained up to themelting point. After the ion irradiation, it transforms tothe cubic disordered structure which does not exist in thephase diagram. For Ni3V and Ni3Al intermetalliccompounds, Vickers hardness decreased with increasing
ion fluence. In the present study, we choose Ni3Nb
intermetallic compound as irradiation targets. Figure 1
shows the phase diagram and crystal structure of Ni3Nballoys. As can be seen in Fig. 1, Ni3Nb shows theorthorhombic ordered structure and it is retained up to themelting point, which is similar to Ni3Al. As comparedwith Ni3V and Ni3Al, however, the lattice structure ofNi3Nb is very complicated. In this report, we will show
the effect of energetic ion irradiation on Ni3Nbintermetallic compound.

A Ni3Nb alloy was prepared by using 99.99 wt.% Niand 99.99 wt.% Nb. An alloy ingot was made by arc
melting under an argon gas atmosphere. It was thermallyannealed at 1273 K for 96 h under vacuum followed byfurnace cooling at a cooling rate of 10 K/min. After theannealing, the ingot was cut into the sheets with thedimension of 1 × 1 × 0.1 cm3. They were irradiated atroom temperature with 16 MeV Au5+ ions by using the 3
MV tandem accelerator at Takasaki Ion accelerators for
Advanced Radiation Application (TIARA). The ion
fluences were from 1 × 1012 to 7 × 1015 cm-2. After the ion
irradiation, we performed the surface x-ray diffraction
measurement as an evaluation method of lattice structurechange.
Also, we performed the extended X-ray absorption finestructure (EXAFS) measurement as a lattice structure
analysis. It is a useful tool for the observation of local
atomic arrangements around selected atoms. Furthermore,this measurement is nondestructive testing, which isdifferent from TEM observations. To observe the localstructures around Nb atoms in the lattice structure of theNi3Nb specimens, we performed the EXAFS
measurements around the Nb K absorption edge (18.9keV) at the 27B beamline of the synchrotron radiation
facility of High Energy Accelerator ResearchOrganization (KEK-PF). The EXAFS spectra wereobtained using a 7 element germanium detector by thefluorescence method at room temperature. We used thecomputer software, WinXas, for analyzing the obtained
EXAFS spectra. In the analyses, all EXAFS spectra were
Fourier transformed using k3 weighting with the k range
from 2 - 3 to 10 - 15 Å-1.
The surface hardness change was estimated by using aVickers hardness tester at room temperature with a loadof 10 gf. The time interval of each indentation was kept at
10 seconds.
3Fig. 1 The partial phase diagram and crystal structure ofNi3Nb intermetallic compound2Experiment

Results and Discussion
Fig. 2 (a) shows the results of surface X-ray diffraction
overall spectra for the unirradiated and irradiatedspecimens. Fig. 2 (b) shows the spectra magnified at thenarrow range from 38° to 48°. For unirradiated Ni3Nb, thefundamental 002, 201, 020, 012 and 211 peaks are clearlyobserved. However, for the Au ion irradiated Ni 3Nb, thefundamental peaks tend to disappear with an increase in
ion fluence. Finally, they completely disappear and broadPhoton Factory Activity Report 2014 #32 (2015 ) B
peak appears at around 42° by Au ion irradiation with afluence of 5×1014/cm2. This result suggests that Ni3Nbtransforms from the orthorhombic ordered structure (D0alattice structure) to the amorphous state by ion irradiation
at room temperature.

conventional fact that the value of hardness for theamorphous state is larger than that for the crystal structure.
Fig. 5 shows the Vickers hardness changes for Ni3V,
Ni3Al and Ni3Nb. For Ni3V and Ni3Al intermetallic
compounds, Vickers hardness decreases with increasing
ion fluence. The Burger’s vector of the dislocation for theordered tetragonal or L12 structure is larger than that forthe disordered FCC structure. Therefore, the disordered
FCC structure is more deformable than the ordered
tetragonal or L12 structure. On the other hand, for Ni3Nb
the Vickers hardness increases with increasing ion fluence.
As Ni3Nb transforms from the ordered structure to theamorphous state, we cannot explain the hardness change
by using the dislocation theory.
The present result implies that energetic ion irradiation
can be used to control the surface hardness for Ni3Nb
intermetallic compound.

Fig. 3 FT EXAFS spectra around Nb K absorption edge
for the unirradiated and irradiated specimens

Fig. 2 (a) Surface x-ray diffraction spectra of theunirradiated and irradiated Ni3Nb intermetallic compound(b) Surface x-ray diffraction spectra at the diffraction
angles of 38° – 48°
Fig. 3 shows the Fourier transformed (FT) EXAFS
spectra around Nb K absorption edge for the unirradiatedand irradiated Ni3Nb. The intensity of each peakdecreases with an increase in ion fluence. This result
implies that the atomic arrangement around Nb atoms isdisordered by the irradiation.
Fig. 4 shows the Vickers hardness as a function of ion
fluence. The hardness of Ni3Nb intermetallic compound isincreased by the irradiation-induced lattice structuretransformation. This result corresponds to theFig. 4 Vickers hardness as a function of Au ion fluencePhoton Factory Activity Report 2014 #32 (2015 ) B

Fig. 5 Relative change in hardness for Ni3Nb. For
comparison, data for Ni3Al and Ni3V are also plotted.
To investigate the thermal stability of the amorphousstate induced by ion irradiation for Ni3Nb intermetalliccompound,annealingexperiments
atelevatedtemperatures for some ion-irradiated Ni3Nb specimens are
now in progress.
References[1] A. Hashimoto et al., Jpn. J. Appl. Phys., 53 (2014)
05FC08[2] H. Yoshizaki et al., Nucl. Instr. Meth. B., 354 (2015)287-291
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