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Irradiation effect of swift heavy ion for Zr50Cu40Al10 bulk glassy alloy
Nuclear Instruments and Methods in Physics Research B 314 (2013) 122–124
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Irradiation effect of swift heavy ion for Zr50Cu40Al10 bulk glassy alloy Naoto Onodera a, Akito Ishii a, Kouji Ishii a, Akihiro Iwase a, Yoshihiko Yokoyama b, Yuichi Saitoh c, Norito Ishikawa d, Atsushi Yabuuchi e, Fuminobu Hori a,⇑ a
Department of Materials Science, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan c Japan Atomic Energy Agency (JAEA), Takasaki Advanced Radiation Research Institute, 1233, Watanuki-machi, Takasaki, Gunma 370-1292, Japan d Japan Atomic Energy Agency (JAEA), Tokai Research and Development Center, Naka-ku, Ibaraki 319-1195, Japan e Research Organization for the 21st Century, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan b
a r t i c l e
i n f o
Article history: Received 30 November 2012 Received in revised form 30 March 2013 Accepted 4 April 2013 Available online 19 April 2013 Keywords: Amorphous Free volume Positron annihilation spectroscopy Radiation damage Stopping power
a b s t r a c t It has been reported that heavy ion irradiation causes softening in some cases of Zr-based bulk metallic glass alloys. However, the fundamental mechanisms of such softening have not been clarified yet. In this study, Zr50Cu40Al10 bulk glassy alloys were irradiated with heavy ions of 10 MeV I at room temperature. The maximum fluence was 3 1014 ions/cm2. The positron annihilation measurements have performed before and after irradiation to investigate changes in free volume. We discuss the relationship between the energy loss and local open volume change after 10 MeV I irradiation compared with those obtained for 200 MeV Xe and 5 MeV Al. The energy loss analysis in ion irradiation for the positron lifetime has revealed that the decreasing trend of positron lifetime is well expressed as a function of total electronic energy deposition rather than total elastic energy deposition. It means that the positron lifetime change by the irradiation has a relationship with the inelastic collisions with electrons during heavy ion irradiation. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction The bulk glassy alloy, which has no long-range atomic ordered structure, possesses attractive mechanical properties such as high strength and toughness due to its superior stabilized structure, while it is nonequilibrium state [1]. Therefore, energy deposition leads to change in local structure correlated with mechanical properties and/or ‘‘free volume’’, which means frozen excess open volume containing in glassy structure [2,3]. So far, it has been reported that thin films of glassy alloys are crystallized due to high-energy electron [4] and ion irradiation [5,6]. On the other hand, in our previous studies, no crystallization has taken place in bulk size of Zr50Cu40Al10 glassy alloy under any kinds of irradiation such as high-energy electron, light ion and heavy ion irradiation [7–9]. In addition, we have also observed the irradiation-induced change in hardness and free volume which largely depends on the radiation species [7,8]. Especially, swift heavy ion irradiation has caused softening in hardness correlated with decrease in free volume size [9]. Recently, Raghavan et al. have reported that swift heavy ion irradiation to Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk glassy alloy not only causes softening but also increases plasticity through uniform deformation [10,11]. ⇑ Corresponding author. E-mail address: [email protected] (F. Hori). 0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.04.034
However, the fundamental mechanisms of radiation effects with swift heavy ion irradiation for the ‘‘bulk’’ glassy alloys have not been clarified yet. In this study, in order to understand the origin of radiation effect of swift heavy ion for Zr50Cu40Al10 bulk glassy alloy, we performed 10 MeV I ion irradiation in addition to our previous experiments of 200 MeV Xe ions [7,9] and 5 MeV Al ions [9] irradiation and tried to discuss the relationship between changes in free volume and irradiation parameters. 2. Experimental procedure The rod shape of Zr50Cu40Al10 bulk glassy alloy samples were fabricated by the tilt casting method in an arc furnace and cut into the size of U 8 mm 0.6 mm disc [12]. They were irradiated with 10 MeV I3+ ions at room temperature by using a tandem type accelerator at the Japanese Atomic Energy Research Agency (JAEA) Takasaki and Tokai, Japan. The fluence of I ion irradiation were 4.0 1013 and 3.0 1014 ions/cm2. Positron annihilation lifetime and coincidence Doppler broadening measurements were performed for these samples by using 22-NaCl as a positron source. All the positron annihilation lifetime spectra were analyzed by POSITRONFIT program [13]. The statistical error of positron lifetime s is less than 1 ps. The maximum depth of 10 MeV I ion irradiation damage estimated by TRIM simulation [14] is about 3 lm for Zr50Cu40Al10. This value is close to those for 5 MeV Al ion
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N. Onodera et al. / Nuclear Instruments and Methods in Physics Research B 314 (2013) 122–124
(3 lm) and 200 MeV Xe ion (13 lm) irradiation. To confirm crystallinities of the samples due to irradiation, X-ray diffraction (XRD) measurement was also performed.
2.2
3. Results and discussion
1.8
Fig. 1 shows X-ray diffraction spectra for Zr50Cu40Al10 bulk glassy alloy before and after 10 MeV I ions irradiation. In this figure, no crystalline peak appears at all by ion irradiation. This phenomenon can be seen the XRD results for low energy of 5 MeV Al ion and high energy of 200 MeV Xe ion irradiation [7,9]. This shows the amorphous state in this kind of bulk glassy alloy is retained by any energy of ion irradiations. Fig. 2 shows CDB profile for the bulk glassy alloy irradiated with 10 MeV I ions in the form of ratio of the CDB intensity to that for Al metal. In general, it is known that the Doppler broadening profile directly reflects the chemical environment around the free volume where positron annihilated [15]. It has been reported that no long range atomic reordering for Zr50Cu40Al10 bulk glassy alloy during structural relaxation by the annealing shows unchanged CDB profile [3]. As seen in Fig. 2, it cannot be seen any significant change in the CDB ratio profile by ion irradiation. Similar results have been obtained in the case of 200 MeV Xe ions and 5 MeV Al ions irradiation [7,9]. That is, no long-range atomic reordering around free volume may have occurred by the irradiation. On the other hand, we found unique relationship between change in positron lifetime and irradiation condition. The positron lifetime value before irradiation is 165 ps. We tried all positron lifetime spectra to decompose into two or more components in analysis, but only one component was analyzed in all samples. This reveals that the distribution of free volume size has only single peak curve after ion irradiation. Fig. 3(a) and (b) shows the positron lifetime change Ds by 200 MeV Xe ions [7], 5 MeV Al ions [9] and 10 MeV I ions irradiation as a function of total electronic energy deposition defined as Se U, and total elastic energy deposition Sn U for Zr50Cu40Al10 bulk glassy alloy. Se and Sn denote the electronic energy loss and the elastic energy loss, respectively. The irradiation parameters of Se U and Sn U, calculated by TRIM code [14], are listed in Table 1. Generally, energetic ions, which penetrate into a solid, lose their energy via nearly two independent processes: one is an inelastic collision with electrons and other is an elastic collision with the nuclei of target atoms. Especially, electronic excitation due to high electronic energy loss Se is assumed to cause ‘‘thermal spike’’ or ‘‘Coulomb explosion’’ in variety of materials. It is well known that high-energy heavy ions cause high-density electronic excitations along their ion beam path in solids, such as ‘‘ion tracks’’
1.6
2
Intensity (a.u.)
13
2
10 MeV-I 4x10 /cm
before irradiation
Ratio to Al
before irradiation 10 MeV I 3x10
30
40
50 60 2θ θ (degree)
70
Al
0.8 Zr
0.6 0
0.005 0.01 0.015 0.02 0.025 Electron momentum p (m0 c)
Fig. 1. X-ray diffraction spectra for Zr50Cu40Al10 bulk glassy alloy after 10 MeV I ion irradiation.
0.03
Fig. 2. The CDB profile of 10 MeV I ion irradiated Zr50Cu40Al10 bulk glassy alloy expressed as the form of ratio of the CDB intensity to that for Al metal. The CDB spectra of before-irradiated specimen, pure Zr and Cu metals are also plotted.
Change in positron lifetime Δτ (ps)
5
(a) (τ = 165)
0
-5
-10 200 MeV - Xe ions 10 MeV - I ions 5 MeV - Al ions -15 13 10
14
15
10
10
Se 5
16
10
17
10
Φ (MeV/mg)
(b) (τ = 165)
0
-5
-10 200 MeV - Xe ions 10 MeV - I ions 5 MeV - Al ions -15 12 10
80
2
ions/cm
1.2
10
13
10
Sn
20
14
Cu
1.4
1
Change in positron lifetime Δτ (ps)
14
10 MeV-I 3x10 /cm
Zr50 Cu 40Al10
2
14
10
15
10
16
Φ (MeV/mg)
Fig. 3. Change in positron lifetime Ds by swift heavy ion irradiation as a function of (a) total electronic energy deposition: Se U and (b) total elastic energy deposition: Sn U for Zr50Cu40Al10 bulk glassy alloy. The lifetime value before irradiation was 165 ps as shown.
124
N. Onodera et al. / Nuclear Instruments and Methods in Physics Research B 314 (2013) 122–124 Table 1 Calculated irradiation parameters: Sn U, total elastic energy deposition; Se U, total electronic energy deposition for Zr50Cu40Al10 bulk glassy alloy irradiated with 10 MeV I ion irradiation, 5 MeV Al ion.
10 MeV I 5 MeV Al 200 MeV Xe
Irradiation fluence U (ions/cm2)
Total elastic energy deposition Sn U (MeV/mg)
Total electronic energy deposition Se U (MeV/mg)
4 1013 3 1014 3 1014 1 1013 1 1014
8.5 1013 6.4 1014 5.8 1013 8.7 1012 8.7 1013
1.4 1014 1.1 1015 7.2 1014 2.2 1014 2.2 1015
in insulators [16,17] or ‘‘radiation annealing’’ of defects in FCC metal below 10 K [18] through electron–phonon interaction. In Fig. 3, we can observe the decrease in positron lifetime, which reflects the decrease in size of free volume, in any irradiation case. Moreover, the decreasing trend of positron lifetime is well expressed as a function of total electronic energy deposition rather than total elastic energy deposition. It means that the positron lifetime change by the irradiation has a relationship with the inelastic collisions with electrons during heavy ion irradiation. Especially, in Fig. 3(b), data are not scattered without the data of 10 MeV I, while the data looks scattered because of the presence of 10 MeV I data. This seems to be one of the merits of adopting 10 MeV I ion in the present study. This phenomenon is not confirmed in case of electron irradiation and low energy ion irradiation, such as 180 keV He [8]. Moreover, this decreasing trend of positron lifetime is similar to that in case of structural relaxation by heat treatment. However, the trend of mechanical property change by annealing is not much as that of heavy ion irradiation [9]. Therefore, heavy ion irradiation affects local structure change, especially around free volume, with the tendency of atomic relaxation by annealing, but their reconstructed local structure is not necessarily the same. This difference may be caused by different local atomic re-arrangement process, that is, self migration of atoms by annealing and local atomic disturbance with high-energy deposition such as ‘‘thermal spike’’ or ‘‘Coulomb explosion’’ by heavy ion irradiation. 4. Summary The relationship between free volume change and total electronic- or elastic energy deposition through swift heavy ion irradiation for Zr50Cu40Al10 bulk glassy alloy was studied by employing positron annihilation spectroscopy. It follows from these experiments that free volume size decreases by swift heavy ion irradiation depending not on the amount of elastic- but electronic energy deposition.
Acknowledgements Authors would like to express cordial thanks to technical staffs for ion irradiation at Japan Atomic Energy Agency. This work was also performed under the inter-university cooperative research program of the Advanced Research Center of Metallic Glasses, Institute for Materials Research, Tohoku University. References [1] A. Inoue, Acta Mater. 48 (2000) 279–306. [2] Y. Yokoyama, Y. Akeno, T. Yamasaki, P.K. Liaw, R.A. Buchanan, A. Inoue, Mater. Trans. 46 (12) (2005) 2755–2761. [3] A. Ishii, F. Hori, A. Iwase, Y. Fukumoto, Y. Yokoyama, T.J. Konno, Mater. Trans. 49 (9) (2008) 1975–1978. [4] T. Nagase, T. Hosokawa, K. Takizawa, Y. Umakoshi, Intermetallics 17 (2009) 657–668. [5] J. Carter, E.G. Fu, G. Bassiri, et al., Nucl. Instr. Meth. B 267 (2009) 1518–1521. [6] J. Carter, E.G. Fu, M. Martin, et al., Nucl. Instrum. Meth. B 267 (2009) 2827– 2831. [7] Y. Fukumoto, A. Ishii, A. Iwase, Y. Yokoyama, F. Hori, J. Phys.: Conf. Ser. 225 (2010) 012010. [8] F. Hori, N. Onodera, Y. Fukumoto, A. Iwase, A. Kawasuso, A. Yabuuchi, M. Maekawa, Y. Yokoyama, J. Phys.: Conf. Ser. 262 (2011) 012025. [9] N. Onodera, A. Ishii, Y. Fukumoto, A. Iwase, Y. Yokoyama, F. Hori, Nucl. Instrum. Meth. B 282 (2012) 1–3. [10] R. Raghavan, K. Boopathy, R. Ghisleni, M.A. Pouchon, U. Ramamurty, J. Michler, Scripta Mater. 62 (2010) 462–465. [11] R. Raghavan, B. Kombaiah, M. Dobeli, R. Erni, U. Ramamurty, J. Michler, Mater. Sci. Eng. A 532 (2012) 407–413. [12] Y. Yokoyama, K. Fukaura, A. Inoue, Intermetallics 10 (2002) 1113–1124. [13] P. Kirkegaard, M. Eldrup, O.E. Mogensen, N.J. Pedersen, Comp. Phys. Commun. 23 (1981) 307. [14]
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Irradiation effect of swift heavy ion for Zr50Cu40Al10 bulk glassy alloy Naoto Onodera a, Akito Ishii a, Kouji Ishii a, Akihiro Iwase a, Yoshihiko Yokoyama b, Yuichi Saitoh c, Norito Ishikawa d, Atsushi Yabuuchi e, Fuminobu Hori a,⇑ a
Department of Materials Science, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan c Japan Atomic Energy Agency (JAEA), Takasaki Advanced Radiation Research Institute, 1233, Watanuki-machi, Takasaki, Gunma 370-1292, Japan d Japan Atomic Energy Agency (JAEA), Tokai Research and Development Center, Naka-ku, Ibaraki 319-1195, Japan e Research Organization for the 21st Century, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan b
a r t i c l e
i n f o
Article history: Received 30 November 2012 Received in revised form 30 March 2013 Accepted 4 April 2013 Available online 19 April 2013 Keywords: Amorphous Free volume Positron annihilation spectroscopy Radiation damage Stopping power
a b s t r a c t It has been reported that heavy ion irradiation causes softening in some cases of Zr-based bulk metallic glass alloys. However, the fundamental mechanisms of such softening have not been clarified yet. In this study, Zr50Cu40Al10 bulk glassy alloys were irradiated with heavy ions of 10 MeV I at room temperature. The maximum fluence was 3 1014 ions/cm2. The positron annihilation measurements have performed before and after irradiation to investigate changes in free volume. We discuss the relationship between the energy loss and local open volume change after 10 MeV I irradiation compared with those obtained for 200 MeV Xe and 5 MeV Al. The energy loss analysis in ion irradiation for the positron lifetime has revealed that the decreasing trend of positron lifetime is well expressed as a function of total electronic energy deposition rather than total elastic energy deposition. It means that the positron lifetime change by the irradiation has a relationship with the inelastic collisions with electrons during heavy ion irradiation. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction The bulk glassy alloy, which has no long-range atomic ordered structure, possesses attractive mechanical properties such as high strength and toughness due to its superior stabilized structure, while it is nonequilibrium state [1]. Therefore, energy deposition leads to change in local structure correlated with mechanical properties and/or ‘‘free volume’’, which means frozen excess open volume containing in glassy structure [2,3]. So far, it has been reported that thin films of glassy alloys are crystallized due to high-energy electron [4] and ion irradiation [5,6]. On the other hand, in our previous studies, no crystallization has taken place in bulk size of Zr50Cu40Al10 glassy alloy under any kinds of irradiation such as high-energy electron, light ion and heavy ion irradiation [7–9]. In addition, we have also observed the irradiation-induced change in hardness and free volume which largely depends on the radiation species [7,8]. Especially, swift heavy ion irradiation has caused softening in hardness correlated with decrease in free volume size [9]. Recently, Raghavan et al. have reported that swift heavy ion irradiation to Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk glassy alloy not only causes softening but also increases plasticity through uniform deformation [10,11]. ⇑ Corresponding author. E-mail address: [email protected] (F. Hori). 0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.04.034
However, the fundamental mechanisms of radiation effects with swift heavy ion irradiation for the ‘‘bulk’’ glassy alloys have not been clarified yet. In this study, in order to understand the origin of radiation effect of swift heavy ion for Zr50Cu40Al10 bulk glassy alloy, we performed 10 MeV I ion irradiation in addition to our previous experiments of 200 MeV Xe ions [7,9] and 5 MeV Al ions [9] irradiation and tried to discuss the relationship between changes in free volume and irradiation parameters. 2. Experimental procedure The rod shape of Zr50Cu40Al10 bulk glassy alloy samples were fabricated by the tilt casting method in an arc furnace and cut into the size of U 8 mm 0.6 mm disc [12]. They were irradiated with 10 MeV I3+ ions at room temperature by using a tandem type accelerator at the Japanese Atomic Energy Research Agency (JAEA) Takasaki and Tokai, Japan. The fluence of I ion irradiation were 4.0 1013 and 3.0 1014 ions/cm2. Positron annihilation lifetime and coincidence Doppler broadening measurements were performed for these samples by using 22-NaCl as a positron source. All the positron annihilation lifetime spectra were analyzed by POSITRONFIT program [13]. The statistical error of positron lifetime s is less than 1 ps. The maximum depth of 10 MeV I ion irradiation damage estimated by TRIM simulation [14] is about 3 lm for Zr50Cu40Al10. This value is close to those for 5 MeV Al ion
123
N. Onodera et al. / Nuclear Instruments and Methods in Physics Research B 314 (2013) 122–124
(3 lm) and 200 MeV Xe ion (13 lm) irradiation. To confirm crystallinities of the samples due to irradiation, X-ray diffraction (XRD) measurement was also performed.
2.2
3. Results and discussion
1.8
Fig. 1 shows X-ray diffraction spectra for Zr50Cu40Al10 bulk glassy alloy before and after 10 MeV I ions irradiation. In this figure, no crystalline peak appears at all by ion irradiation. This phenomenon can be seen the XRD results for low energy of 5 MeV Al ion and high energy of 200 MeV Xe ion irradiation [7,9]. This shows the amorphous state in this kind of bulk glassy alloy is retained by any energy of ion irradiations. Fig. 2 shows CDB profile for the bulk glassy alloy irradiated with 10 MeV I ions in the form of ratio of the CDB intensity to that for Al metal. In general, it is known that the Doppler broadening profile directly reflects the chemical environment around the free volume where positron annihilated [15]. It has been reported that no long range atomic reordering for Zr50Cu40Al10 bulk glassy alloy during structural relaxation by the annealing shows unchanged CDB profile [3]. As seen in Fig. 2, it cannot be seen any significant change in the CDB ratio profile by ion irradiation. Similar results have been obtained in the case of 200 MeV Xe ions and 5 MeV Al ions irradiation [7,9]. That is, no long-range atomic reordering around free volume may have occurred by the irradiation. On the other hand, we found unique relationship between change in positron lifetime and irradiation condition. The positron lifetime value before irradiation is 165 ps. We tried all positron lifetime spectra to decompose into two or more components in analysis, but only one component was analyzed in all samples. This reveals that the distribution of free volume size has only single peak curve after ion irradiation. Fig. 3(a) and (b) shows the positron lifetime change Ds by 200 MeV Xe ions [7], 5 MeV Al ions [9] and 10 MeV I ions irradiation as a function of total electronic energy deposition defined as Se U, and total elastic energy deposition Sn U for Zr50Cu40Al10 bulk glassy alloy. Se and Sn denote the electronic energy loss and the elastic energy loss, respectively. The irradiation parameters of Se U and Sn U, calculated by TRIM code [14], are listed in Table 1. Generally, energetic ions, which penetrate into a solid, lose their energy via nearly two independent processes: one is an inelastic collision with electrons and other is an elastic collision with the nuclei of target atoms. Especially, electronic excitation due to high electronic energy loss Se is assumed to cause ‘‘thermal spike’’ or ‘‘Coulomb explosion’’ in variety of materials. It is well known that high-energy heavy ions cause high-density electronic excitations along their ion beam path in solids, such as ‘‘ion tracks’’
1.6
2
Intensity (a.u.)
13
2
10 MeV-I 4x10 /cm
before irradiation
Ratio to Al
before irradiation 10 MeV I 3x10
30
40
50 60 2θ θ (degree)
70
Al
0.8 Zr
0.6 0
0.005 0.01 0.015 0.02 0.025 Electron momentum p (m0 c)
Fig. 1. X-ray diffraction spectra for Zr50Cu40Al10 bulk glassy alloy after 10 MeV I ion irradiation.
0.03
Fig. 2. The CDB profile of 10 MeV I ion irradiated Zr50Cu40Al10 bulk glassy alloy expressed as the form of ratio of the CDB intensity to that for Al metal. The CDB spectra of before-irradiated specimen, pure Zr and Cu metals are also plotted.
Change in positron lifetime Δτ (ps)
5
(a) (τ = 165)
0
-5
-10 200 MeV - Xe ions 10 MeV - I ions 5 MeV - Al ions -15 13 10
14
15
10
10
Se 5
16
10
17
10
Φ (MeV/mg)
(b) (τ = 165)
0
-5
-10 200 MeV - Xe ions 10 MeV - I ions 5 MeV - Al ions -15 12 10
80
2
ions/cm
1.2
10
13
10
Sn
20
14
Cu
1.4
1
Change in positron lifetime Δτ (ps)
14
10 MeV-I 3x10 /cm
Zr50 Cu 40Al10
2
14
10
15
10
16
Φ (MeV/mg)
Fig. 3. Change in positron lifetime Ds by swift heavy ion irradiation as a function of (a) total electronic energy deposition: Se U and (b) total elastic energy deposition: Sn U for Zr50Cu40Al10 bulk glassy alloy. The lifetime value before irradiation was 165 ps as shown.
124
N. Onodera et al. / Nuclear Instruments and Methods in Physics Research B 314 (2013) 122–124 Table 1 Calculated irradiation parameters: Sn U, total elastic energy deposition; Se U, total electronic energy deposition for Zr50Cu40Al10 bulk glassy alloy irradiated with 10 MeV I ion irradiation, 5 MeV Al ion.
10 MeV I 5 MeV Al 200 MeV Xe
Irradiation fluence U (ions/cm2)
Total elastic energy deposition Sn U (MeV/mg)
Total electronic energy deposition Se U (MeV/mg)
4 1013 3 1014 3 1014 1 1013 1 1014
8.5 1013 6.4 1014 5.8 1013 8.7 1012 8.7 1013
1.4 1014 1.1 1015 7.2 1014 2.2 1014 2.2 1015
in insulators [16,17] or ‘‘radiation annealing’’ of defects in FCC metal below 10 K [18] through electron–phonon interaction. In Fig. 3, we can observe the decrease in positron lifetime, which reflects the decrease in size of free volume, in any irradiation case. Moreover, the decreasing trend of positron lifetime is well expressed as a function of total electronic energy deposition rather than total elastic energy deposition. It means that the positron lifetime change by the irradiation has a relationship with the inelastic collisions with electrons during heavy ion irradiation. Especially, in Fig. 3(b), data are not scattered without the data of 10 MeV I, while the data looks scattered because of the presence of 10 MeV I data. This seems to be one of the merits of adopting 10 MeV I ion in the present study. This phenomenon is not confirmed in case of electron irradiation and low energy ion irradiation, such as 180 keV He [8]. Moreover, this decreasing trend of positron lifetime is similar to that in case of structural relaxation by heat treatment. However, the trend of mechanical property change by annealing is not much as that of heavy ion irradiation [9]. Therefore, heavy ion irradiation affects local structure change, especially around free volume, with the tendency of atomic relaxation by annealing, but their reconstructed local structure is not necessarily the same. This difference may be caused by different local atomic re-arrangement process, that is, self migration of atoms by annealing and local atomic disturbance with high-energy deposition such as ‘‘thermal spike’’ or ‘‘Coulomb explosion’’ by heavy ion irradiation. 4. Summary The relationship between free volume change and total electronic- or elastic energy deposition through swift heavy ion irradiation for Zr50Cu40Al10 bulk glassy alloy was studied by employing positron annihilation spectroscopy. It follows from these experiments that free volume size decreases by swift heavy ion irradiation depending not on the amount of elastic- but electronic energy deposition.
Acknowledgements Authors would like to express cordial thanks to technical staffs for ion irradiation at Japan Atomic Energy Agency. This work was also performed under the inter-university cooperative research program of the Advanced Research Center of Metallic Glasses, Institute for Materials Research, Tohoku University. References [1] A. Inoue, Acta Mater. 48 (2000) 279–306. [2] Y. Yokoyama, Y. Akeno, T. Yamasaki, P.K. Liaw, R.A. Buchanan, A. Inoue, Mater. Trans. 46 (12) (2005) 2755–2761. [3] A. Ishii, F. Hori, A. Iwase, Y. Fukumoto, Y. Yokoyama, T.J. Konno, Mater. Trans. 49 (9) (2008) 1975–1978. [4] T. Nagase, T. Hosokawa, K. Takizawa, Y. Umakoshi, Intermetallics 17 (2009) 657–668. [5] J. Carter, E.G. Fu, G. Bassiri, et al., Nucl. Instr. Meth. B 267 (2009) 1518–1521. [6] J. Carter, E.G. Fu, M. Martin, et al., Nucl. Instrum. Meth. B 267 (2009) 2827– 2831. [7] Y. Fukumoto, A. Ishii, A. Iwase, Y. Yokoyama, F. Hori, J. Phys.: Conf. Ser. 225 (2010) 012010. [8] F. Hori, N. Onodera, Y. Fukumoto, A. Iwase, A. Kawasuso, A. Yabuuchi, M. Maekawa, Y. Yokoyama, J. Phys.: Conf. Ser. 262 (2011) 012025. [9] N. Onodera, A. Ishii, Y. Fukumoto, A. Iwase, Y. Yokoyama, F. Hori, Nucl. Instrum. Meth. B 282 (2012) 1–3. [10] R. Raghavan, K. Boopathy, R. Ghisleni, M.A. Pouchon, U. Ramamurty, J. Michler, Scripta Mater. 62 (2010) 462–465. [11] R. Raghavan, B. Kombaiah, M. Dobeli, R. Erni, U. Ramamurty, J. Michler, Mater. Sci. Eng. A 532 (2012) 407–413. [12] Y. Yokoyama, K. Fukaura, A. Inoue, Intermetallics 10 (2002) 1113–1124. [13] P. Kirkegaard, M. Eldrup, O.E. Mogensen, N.J. Pedersen, Comp. Phys. Commun. 23 (1981) 307. [14]