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In-situ observation of the dynamic behavior of bubbles in aluminum during 10 keV H2+ ion irradiation and successive annealing
Journal of Nuclear Materials 179-181 (1991) 1011-1014 North-Holland
1011
In-situ observation of the dynamic behavior of bubbles in aluminum during 10 keV Hl ion irradiation and successive annealing S. Furuno ‘, K. Hojou ‘, H. Otsu ‘, K. hi
‘, N. Kamigaki ’ and T. Kino 3
’ Departmentof Chemistry,Japan Atomic Energy Research Institute,Tohai-mum, Zbarahi319-11, Japan 2 Fact&y of Education,Ehime University,Matsuyama790, Japan 3 Fact&y of Science, Hiroshima University,Hiroshima 730, Japan
The behavior of bubbles in aluminum during 10 keV H z ion irradiation and successive annealing was investigated by in-situ observation in an electron microscope. Bubbles were formed by irradiation at 300 K, but no bubbles were observed at 113 and 373 K. After irradiation at 113 K, bubbles were found to be formed during annealing from 113 to 300 K. During annealing from 300 to 498 K, smaller bubbles began to &rink and disappear at a lower temperature in comparison with larger bubbles. From these experiments, the activation energy for bubble shrinkage was found to be about 1 eV, and the binding energy of a vacancy to a bubble was inferred to be about 0.4 eV. 1. Introduction Aluminum is one of the candidate materials for a fusion reactor constituent because of its low atomic number and low activation [1,2]. In order to simulate the structural and chemical changes due to plasma-wall interactions, ion irradiation experiments have been widely performed. Among these activities [3-S], m-situ observation of the dynamic process of damage evolution is a unique technique by which to establish a reliable physical model. In a previous paper [4], we reported the results of an observation of the dynamic behavior of bubbles and blisters in helium ion irradiated aluminum observed by using equipment recently developed in our laboratory
PI.
The present paper reports the results of m-situ observation of the dynamic behavior of bubbles in aluminum during 10 keV Hi ion irradiation and successive annealing steps. 2. Experimental procedure Specimens were zone refined aluminum of 99.9999% purity [6]. Thin films suitable for electron microscope observation were made by electropolishing in a mixed solution of ethanol and perchloric acid in the ratio of 4: 1. Ion irradiation and simultaneous observation were performed by using an electron microscope of JEM1OOC type equipped with a Duo-plasmatron type ion gun with an accelerating voltage up to 10 keV. A mass selected ion beam is incident at an angle of 72” to the surface of the specimen. The 10 keV Hz ion irradiation was performed at 113-373 K with the fhtx of 6 X 1017-1.2 X lo’* ions/m2 s. After irradiation at 113 K, the specimens were annealed from 113 to 300 K in the electron microscope. After the annealing mentioned above, the same speci-
men was annealed from 300 to 498 K. The temperature was raised stepwise, 25 K steps for 10 min intervals. Results of in-situ observation during ion irradiation and successive annealing were recorded with a VTR through a TV camera. 3. Results and discussion 3.1. Formation of bubbles and dislocation loops during irradiation at various temperatures In the case of irradiation at 300 K with the flw of 1.2 X lo’* ions/m2 s dislocation loops were produced at the initial stage and then small bubbles were formed. These bubbles grow without an appreciable increase in number and slowly coalesced, maintaining a dumb-bell shape for a long time after coalescence as shown in figs. l(a) to (h). This was in contrast to the case of He+ ion irradiation at 573 K, where a violent coalescence of bubbles was observed [2]. The reason for this slow coalescence is considered to be due to both the lower inner pressure and lower temperature in comparison with the case of He+ ion irradiation. No bubbles were observed during irradiation at 373 and 113 K respectively, but dislocation loops were formed at the initial stage, and then grew and increased in number leading to tangling. It was also seen that dislocation loops not only grew, but some shrank and disappeared. 3.2. Behavior of bubbles and dislocation loops during annealing up to room temperature after the irradiation at 113 K Bubbles were found to be formed during annealing up to 300 K after the irradiation to a fluence of 2.2 x 102’ ions/m2, as shown in fig. 2. Vacancies and hydrogen atoms accumulated in the specimen during irradiation at 113 K would migrate during annealing up to 273 K, resulting in the formation of bubbles.
0022-3115/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)
S. Furino et al. / Dynamic behavior of hydrogen bubbles in Al
1012
Fig. 1. FOImation, growth and coalescence of dislocation loops and bubbles dnring 10 keV Hz irradiation at 300 K with the flu IX of 1.2 X 10” ions/m2 s.
3.3.
Behavior of bubbles during annealing from room
temperature
to 498 K
The specimen where the bubbles were formed by annealing as described in section 3.2 was aged at 300 K
Fig. 2. Bubbles formed during annealing from II3 to 300 K after 10 keV Hz irradiation at 113 K to a fluence of 2.2 X 102’ .ions/m2.
for three days. Then the annealing experiment was performed up to 498 K. The temperature was raised stepwise, 25 K steps for 10 min intervals. The typical results of this in-situ observation are shown in the series of photographs of figs. 3(a)-(h). The small bubbles of about 2.5 nm in radius began to shrink initially and disap’peared at low temperatures near 330 K, and then larger bubbles began to shrink and vanished at higher temperatures. All the bubbles disappeared at 498 K. Another interesting thing seen in these figures is that the bubbles exhibiting a round shape at room temperature produced facets at 323 K and then became roundish again with increasing temperatures. This change to roundish shape in the bubbles is considered to correspond to the change in the inner pressure of bubbles due to the partial emission of hydrogen. From the shrinkage curve of the radius of the bubbles plotted against time at fixed temperature, it is possible to estimate roughly the activation energy for the bubble shrinkage, The shrinkage curves at 498 K for some bubbles are shown in fig 4. This figure shows that the gradient of each curve becomes nearly equal after the radii of each bubble reached about 10 nm. From the gradient of each curve at this point of radius, the activation energy E,, was estimated to be about 1 eV. The nearly equal values for E,, were obtained at other
S. Furino et al. / Dynamic behavior of hydrogen bubbles in Al
Fig. 3. Behavior of bubble shrinkage and disappearance during annealing from 300 to 498 K after 10 keV Hi
lower temperatures for the values of the radius smaller than 10 nm. Therefore the value of 1 eV for E,,, is general for the bubble shrinkage observed in the present experiment. The E,,, can be expressed by E,, = E, + E, - ( Pq - P,,)Q, where E, is the binding energy of a vacancy to a bubble, E,,, is the migration energy of a vacancy, Peq is the outer pressure due to the surface tension of the bubble, Pi, is the inner gas pressure and Q is the atomic volume. Pesti and Pi,!2 are estimated to be two orders magnitude less than 1 eV for a bubble with a radius larger than 10 nm and can be neglected. Accordingly E, is roughly estimated to be about 0.4 eV, because E, is known to be about 0.66 eV [7].
irradiation
at 113 K.
4. Conclusions The results of in-situ observation of the dynamic behavior of bubbles in aluminium during 10 keV Hi ion irradiations and successive annealing were as follows. (1) Bubbles were formed during irradiation at 300 K, but no bubbles were observed by irradiation at 113 and 373 K respectively. (2) Bubbles were formed during annealing up to 300 K after irradiation at 113 K. from 300 to 498 K, the (3) By successive annealing smaller bubbles began to shrink initially and disappeared at lower temperatures, and then larger bubbles began to shrink and vanished at higher temperatures. All the bubbles disappeared at 498 K. energy for bubble shrinkage was (4) The activation estimated to be about 1 eV from the bubble shrinkage curve and consequently the binding energy of a vacancy to a bubble was inferred to be about 0.4 eV.
References Time (min) Fig. 4. Variation
of the radius of some bubbles during annealing at 498 K.
with
time
[l] R.A. Kramer, E.C. Franz, R.H. Wagner, R.R. Guerra, S.P. Ray and W.E. Wahnsiedler, Low-Activation Structural Materials for Fusion Reactors; Extreme Purity Base Al
1014
S. Furino et al. / Dynamic behavior of hydrogen bubbles in AI
Alloy (Alcoa Technical Center) EPRI Report AP-2220 (1982). [2] T. Noda, F. Abe, H. A&i and M. Okada, J. Nucl. Mater. 155-157 (1988) 581. [3] S. Furuno, K. Izui, K. Ono and T. Kino, J. Nucl. Mater. 133 & 134 (1985) 400. [4] S. Furuno, K. Hojou, K. Izui, N. Kamigaki and T. Kino, J. Nucl. Mater. 155-157 (1988) 1149.
[5] K. Hojou, S. Furuno, H. Otsu, K. Izui and T. Tsukamoto, J. Nucl. Mater. 155-157 (1988) 298. [6] T. Kino, E. Hashimoto, N. Kamigaki, K. Kiso and R. Matsushita, Trans. Jpn. Inst. Met. 18 (1977) 305. [7] K. Ono and T. Kino, J. Phys. Sot. Jpn. 44 (1978) 875.
1011
In-situ observation of the dynamic behavior of bubbles in aluminum during 10 keV Hl ion irradiation and successive annealing S. Furuno ‘, K. Hojou ‘, H. Otsu ‘, K. hi
‘, N. Kamigaki ’ and T. Kino 3
’ Departmentof Chemistry,Japan Atomic Energy Research Institute,Tohai-mum, Zbarahi319-11, Japan 2 Fact&y of Education,Ehime University,Matsuyama790, Japan 3 Fact&y of Science, Hiroshima University,Hiroshima 730, Japan
The behavior of bubbles in aluminum during 10 keV H z ion irradiation and successive annealing was investigated by in-situ observation in an electron microscope. Bubbles were formed by irradiation at 300 K, but no bubbles were observed at 113 and 373 K. After irradiation at 113 K, bubbles were found to be formed during annealing from 113 to 300 K. During annealing from 300 to 498 K, smaller bubbles began to &rink and disappear at a lower temperature in comparison with larger bubbles. From these experiments, the activation energy for bubble shrinkage was found to be about 1 eV, and the binding energy of a vacancy to a bubble was inferred to be about 0.4 eV. 1. Introduction Aluminum is one of the candidate materials for a fusion reactor constituent because of its low atomic number and low activation [1,2]. In order to simulate the structural and chemical changes due to plasma-wall interactions, ion irradiation experiments have been widely performed. Among these activities [3-S], m-situ observation of the dynamic process of damage evolution is a unique technique by which to establish a reliable physical model. In a previous paper [4], we reported the results of an observation of the dynamic behavior of bubbles and blisters in helium ion irradiated aluminum observed by using equipment recently developed in our laboratory
PI.
The present paper reports the results of m-situ observation of the dynamic behavior of bubbles in aluminum during 10 keV Hi ion irradiation and successive annealing steps. 2. Experimental procedure Specimens were zone refined aluminum of 99.9999% purity [6]. Thin films suitable for electron microscope observation were made by electropolishing in a mixed solution of ethanol and perchloric acid in the ratio of 4: 1. Ion irradiation and simultaneous observation were performed by using an electron microscope of JEM1OOC type equipped with a Duo-plasmatron type ion gun with an accelerating voltage up to 10 keV. A mass selected ion beam is incident at an angle of 72” to the surface of the specimen. The 10 keV Hz ion irradiation was performed at 113-373 K with the fhtx of 6 X 1017-1.2 X lo’* ions/m2 s. After irradiation at 113 K, the specimens were annealed from 113 to 300 K in the electron microscope. After the annealing mentioned above, the same speci-
men was annealed from 300 to 498 K. The temperature was raised stepwise, 25 K steps for 10 min intervals. Results of in-situ observation during ion irradiation and successive annealing were recorded with a VTR through a TV camera. 3. Results and discussion 3.1. Formation of bubbles and dislocation loops during irradiation at various temperatures In the case of irradiation at 300 K with the flw of 1.2 X lo’* ions/m2 s dislocation loops were produced at the initial stage and then small bubbles were formed. These bubbles grow without an appreciable increase in number and slowly coalesced, maintaining a dumb-bell shape for a long time after coalescence as shown in figs. l(a) to (h). This was in contrast to the case of He+ ion irradiation at 573 K, where a violent coalescence of bubbles was observed [2]. The reason for this slow coalescence is considered to be due to both the lower inner pressure and lower temperature in comparison with the case of He+ ion irradiation. No bubbles were observed during irradiation at 373 and 113 K respectively, but dislocation loops were formed at the initial stage, and then grew and increased in number leading to tangling. It was also seen that dislocation loops not only grew, but some shrank and disappeared. 3.2. Behavior of bubbles and dislocation loops during annealing up to room temperature after the irradiation at 113 K Bubbles were found to be formed during annealing up to 300 K after the irradiation to a fluence of 2.2 x 102’ ions/m2, as shown in fig. 2. Vacancies and hydrogen atoms accumulated in the specimen during irradiation at 113 K would migrate during annealing up to 273 K, resulting in the formation of bubbles.
0022-3115/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)
S. Furino et al. / Dynamic behavior of hydrogen bubbles in Al
1012
Fig. 1. FOImation, growth and coalescence of dislocation loops and bubbles dnring 10 keV Hz irradiation at 300 K with the flu IX of 1.2 X 10” ions/m2 s.
3.3.
Behavior of bubbles during annealing from room
temperature
to 498 K
The specimen where the bubbles were formed by annealing as described in section 3.2 was aged at 300 K
Fig. 2. Bubbles formed during annealing from II3 to 300 K after 10 keV Hz irradiation at 113 K to a fluence of 2.2 X 102’ .ions/m2.
for three days. Then the annealing experiment was performed up to 498 K. The temperature was raised stepwise, 25 K steps for 10 min intervals. The typical results of this in-situ observation are shown in the series of photographs of figs. 3(a)-(h). The small bubbles of about 2.5 nm in radius began to shrink initially and disap’peared at low temperatures near 330 K, and then larger bubbles began to shrink and vanished at higher temperatures. All the bubbles disappeared at 498 K. Another interesting thing seen in these figures is that the bubbles exhibiting a round shape at room temperature produced facets at 323 K and then became roundish again with increasing temperatures. This change to roundish shape in the bubbles is considered to correspond to the change in the inner pressure of bubbles due to the partial emission of hydrogen. From the shrinkage curve of the radius of the bubbles plotted against time at fixed temperature, it is possible to estimate roughly the activation energy for the bubble shrinkage, The shrinkage curves at 498 K for some bubbles are shown in fig 4. This figure shows that the gradient of each curve becomes nearly equal after the radii of each bubble reached about 10 nm. From the gradient of each curve at this point of radius, the activation energy E,, was estimated to be about 1 eV. The nearly equal values for E,, were obtained at other
S. Furino et al. / Dynamic behavior of hydrogen bubbles in Al
Fig. 3. Behavior of bubble shrinkage and disappearance during annealing from 300 to 498 K after 10 keV Hi
lower temperatures for the values of the radius smaller than 10 nm. Therefore the value of 1 eV for E,,, is general for the bubble shrinkage observed in the present experiment. The E,,, can be expressed by E,, = E, + E, - ( Pq - P,,)Q, where E, is the binding energy of a vacancy to a bubble, E,,, is the migration energy of a vacancy, Peq is the outer pressure due to the surface tension of the bubble, Pi, is the inner gas pressure and Q is the atomic volume. Pesti and Pi,!2 are estimated to be two orders magnitude less than 1 eV for a bubble with a radius larger than 10 nm and can be neglected. Accordingly E, is roughly estimated to be about 0.4 eV, because E, is known to be about 0.66 eV [7].
irradiation
at 113 K.
4. Conclusions The results of in-situ observation of the dynamic behavior of bubbles in aluminium during 10 keV Hi ion irradiations and successive annealing were as follows. (1) Bubbles were formed during irradiation at 300 K, but no bubbles were observed by irradiation at 113 and 373 K respectively. (2) Bubbles were formed during annealing up to 300 K after irradiation at 113 K. from 300 to 498 K, the (3) By successive annealing smaller bubbles began to shrink initially and disappeared at lower temperatures, and then larger bubbles began to shrink and vanished at higher temperatures. All the bubbles disappeared at 498 K. energy for bubble shrinkage was (4) The activation estimated to be about 1 eV from the bubble shrinkage curve and consequently the binding energy of a vacancy to a bubble was inferred to be about 0.4 eV.
References Time (min) Fig. 4. Variation
of the radius of some bubbles during annealing at 498 K.
with
time
[l] R.A. Kramer, E.C. Franz, R.H. Wagner, R.R. Guerra, S.P. Ray and W.E. Wahnsiedler, Low-Activation Structural Materials for Fusion Reactors; Extreme Purity Base Al
1014
S. Furino et al. / Dynamic behavior of hydrogen bubbles in AI
Alloy (Alcoa Technical Center) EPRI Report AP-2220 (1982). [2] T. Noda, F. Abe, H. A&i and M. Okada, J. Nucl. Mater. 155-157 (1988) 581. [3] S. Furuno, K. Izui, K. Ono and T. Kino, J. Nucl. Mater. 133 & 134 (1985) 400. [4] S. Furuno, K. Hojou, K. Izui, N. Kamigaki and T. Kino, J. Nucl. Mater. 155-157 (1988) 1149.
[5] K. Hojou, S. Furuno, H. Otsu, K. Izui and T. Tsukamoto, J. Nucl. Mater. 155-157 (1988) 298. [6] T. Kino, E. Hashimoto, N. Kamigaki, K. Kiso and R. Matsushita, Trans. Jpn. Inst. Met. 18 (1977) 305. [7] K. Ono and T. Kino, J. Phys. Sot. Jpn. 44 (1978) 875.