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Radiation damage studies on Ni implanted with high energy He and D ions
Fusion Engineering and Design 41 (1998) 79 – 84
Radiation damage studies on Ni implanted with high energy He and D ions B. Constantinescu *, F. Vasiliu, G. Alexandru Institute of Atomic Physics, POB MO-6, Bucharest, Romania
Abstract The behavior of hydrogen isotopes in metals is very important for the future nuclear fusion reactor. To study deuterium influence on helium pre-irradiated nickel, 0 – 28 MeV He + + and 7 MeV D + beams were used. Thirty, 100 and 300 appm He pre-implanted samples were D + (1018 ions per cm2) irradiated and 1, 10, 100 and 1000 h high vacuum annealed (1273 K). After an electrochemical preparation (Struers jet), they were examined by transmission electron microscopy (TEM). Values for He bubbles’ radii and densities depending on He ions’ doses and annealing periods are reported. Two types of bubbles were observed: ‘small’ bubbles, predominantly in the matrix (from 5 nm radius for 30 appm, 1 h annealing to 35 nm for 300 appm, 100 h annealing) and ‘large’ bubbles, predominantly in the grain boundaries regions, but even in some dislocations (from 30 nm radius for 30 appm, 1 h annealing to 120 nm for 300 appm, 100 h annealing). A unique bubble coarsening mechanism, the Ostwald ripening, is considered. The influence of deuterium on the ‘small’ and ‘large’ bubbles’ radii values is discussed. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction During the last few years, the behavior of helium in metals has gained considerable interest, because it can cause embrittlement and other materials degradation in components of advanced future nuclear energy systems (fast fission and fusion reactors). Most of these effects are caused by the nucleation and growth of helium bubbles which inevitably form at elevated temperature because of the vanishingly small solubility of helium in solids.
* Corresponding author.
Although there is wide agreement upon the principal mechanism leading to helium-induced changes of materials’ properties, evidently a quantitative understanding of these processes requires a solid knowledge about the basic properties of helium in metals. Among others, the density and size distributions of bubbles as a function of helium content, temperature and time of annealing are of particular interest [1]. The first wall of fusion reactor is also subject to high hydrogen ion and atom fluxes. It has been assumed that due to the higher diffusivity and release rate of hydrogen than those of helium in most candidate materials, the effect of hydrogen is minimal. However, the role of hydrogen for mi-
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00209-9
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B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
crostructural changes, such as void swelling, has not been extensively studied. It is established that hydrogen may be trapped at particular defect sites in metals [2]. The purpose of the present study is to determine combined helium-hydrogen effects as trapping of hydrogen around or near helium bubbles and the influence on size distributions of bubbles as a function of helium content and periods of annealing at 1273 K.
2. Experimental Nickel foils (99.995% pure) of 100 mm thickness were annealed at 1373 K for 2 h in a vacuum greater than 10 − 5 Pa. Homogeneous helium implantation at room temperature was achieved by varying the range of the 28 MeV a-beam of the KFA-Julich (Germany) compact cyclotron by a wheel that continuously rotated 50 Al foils of different thickness through the beam [3]. Samples with nominal helium concentrations of 30, 100 and 300 appm were obtained. Subsequently, these samples were deuterium (1018 D + 7 MeV ions cm − 2) at room temperature irradiated by the Bucharest U-120 classical cyclotron [4]. Then, the samples were annealed at 1273 K for 1, 10, 100 and 1000 h in a vacuum. From each of the helium+ deuterium implanted specimen areas, 3 mm disks were punched out. The disks were electrochemically thinned by jet polishing using a TENUPOL STRUERS JET apparatus and two chemical solutions: perchloric acid plus ethanol at 0°C and sulfuric acid plus glycerin at 10°C. The specimens were investigated in a JEOL TEMSCAN 200 CX microscope operated at 200 kV and in a TESLA BS 240 microscope operated at 120 kV. Most of the micrographs were taken in phase contrast under defocusing condition rB and were determined from histograms obtained with a semiautomatic particle size analyzer and, partially, by direct observation, with an uncertainty of at most 9 30%. For the evaluation of bubble densities, CB, the foil thickness determination was made by interference fringes observation which introduces an uncertainty of about 950%.
3. Results and discussion The annealing behavior of helium bubbles forming in nickel after helium implantation at room temperature which is discussed in details in Chernikov et al. and Qiang-Li et al. [1,5] seems to represent a striking example for the effect of the internal pressure on bubble coarsening [6]. So, for annealing temperature above 900 K and high He concentrations (500–5000 appm) the coarsening rate is found to be substantially faster close to the surface of the sample than in the bulk but comparable to the coarsening rate at low He concentrations (5 200 appm). Accordingly, two distinct coarsening branches in an Arrhenius plot of average bubble radii were identified: a weakly activated (rB values from 0.6 at 800 K to 2 nm at 1400 K) one for slow bubble coarsening in the bulk, and a highly activated (rB values from 1 at 1000 K to 800 nm at 1400 K) one for fast bubble coarsening close to the surface (or in the grain
Fig. 1. Mean radius rB of helium bubbles as a function of the He ions doses.
B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
boundaries). This difference may be correlated with differences in the pressure within the bubbles: higher pressure with increasing He concentration in the bulk but a relaxation of an initially high pressure within bubbles sufficiently close to surface (or grain boundaries) due to vacancies provided by the sample surface (or by internal radiation damages). Consequently, the weakly activated branch (slow coarsening) may be attributed to bubbles with high internal pressure which can coarsen by migration and coalescence while Ostwald ripening is completely suppressed. The highly activated branch (fast coarsening) may be attributed to bubbles in which pressure is low or relaxes during the annealing from an initially high to a finally low value. Such bubbles can coarsen by Ostwald ripening which seems to surpass its maximum rate when the pressure relaxes by vacancies originating from implantation damage (bulk bubbles for low He concentrations and grain boundaries bubbles for high He concentrations) or from the surface. Our results are presented in Figs. 1 – 3 (unfortunately, there are some missing points, because some specimens were damaged during thinning). Apparently, there are two categories of bubbles: ‘small’ in bulk (matrix) bubbles (Fig. 4) and ‘large’ (grain boundaries and dislocations) bubbles (Figs. 5 and 6). Evidently, it is a conventional classification, the essential difference being the affiliation of ‘small’ bubbles strictly to matrix and of ‘large’ bubbles strictly to grain boundaries and dislocations. Critical sizes (Fig. 1) to separate them are 30 nm for 1, 10 and 100 h annealing periods and 100 nm for 1000 h annealing period, for all He concentration values. The rB values for small bubbles (6 – 30 nm) are much larger than the values reported in [1] for the same type of bubbles in the case of simple He implantation (1.5 nm for 1273 K), so, we could assume an Ostwald ripening coarsening mechanism via helium, hydrogen (deuterium) and vacancy resolution and reabsorption. Probably, the relaxation of initially over pressurized He bubbles by annealing of the associated He+H (D) dislocation network is quite substantial. As concerning ‘large’ bubbles, our values are slightly larger than in Chernikov et al. [1], the Ostwald ripening being
81
Fig. 2. Mean radius rB of helium bubbles as a function of the annealing periods.
evident. Variations in the implanted helium concentrations (from 30 to 300 appm) have relatively little influence on the mean radius. However, we must find and explain the influence of hydrogen (deuterium) on our data as compared to a simple helium implantation case reported for nickel in Chernikov et al. and Qiang-Li et al. [1,5]. It is assumed that trapped H isotopes could play a role in the triggering of fast Ostwald ripening. In Myers et al. [6], there is an attempt to explain the trapping of H around He bubbles and relate it to a chemisorption-like interaction at the isolated bubbles. In Solovioff et al. [7] a cracking phenomenon generated by hydrogen in the grain boundaries of the nickel, as a result of the greater stress on the material due to the hydride formation is reported. In Kirsanov et al. [8] the (He+ H+ 2V) and (He+ H+ V) clusters are investigated to determine hydrogen influence on the process of helium-vacancy void formation. However, a detailed and qualitative model which
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can help to understand these effects and to estimate the trapping binding energy has not been established. An exception seems to be the 1000-h annealing period data, where a ‘clustering’ phenomenon (Fig. 7) is observed. The appearance of such structures of very large bubbles cannot be explained for the moment. Probably, during this long annealing period an unusual concentration of defects facilitates this very enhanced bubbles coarsening. We could mention that even for 300 appm, 100-h annealing period case, small ‘clusters’ (2–3–4 ‘small’ bubbles in the bulk) were observed. Concerning small bubbles’ volume densities versus annealing periods (Fig. 3), between 1 and 100 h a relatively constant value for all He doses was observed (with only a significant decrease for 300 appm for 100 h, where isolated ‘clusters’ were reported). For 1000 h, due to the strong ‘clustering’ phenomenon above mentioned, the densities
Fig. 4. Helium bubbles in the matrix; 300 appm, 100 h annealing.
values are two orders of magnitude lower (from 1021 to 1019 m − 3).
4. Conclusion
Fig. 3. Volume density of ‘small’ bubbles as a function of the annealing periods.
Concerning possible bubbles’ coarsening mechanisms, from Chernikov et al. [1] results for He concentration values are similar to those of this study, but in the absence of D implantation, matrix bubbles (diameter values less than 1 nm) can coarsen by migration and coalescence of He atoms and vacancies, moderately reduced by the observed high internal pressure, while Ostwald ripening is completely suppressed. This one is observed for grain boundaries’ bubbles in which the pressure is low or relaxes during annealing mainly due to surface vacancies. In our cases, the large diameter values for matrix bubbles (\ 5 nm) exclude high internal pressure for 30–300 appm
B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
83
He concentration values and, consequently, the migration and coalescence mechanism, and suggest even for matrix bubbles the Ostwald ripening mechanism. So, we could assume a relatively important role of hydrogen isotopes trapped in grain boundaries as active vacancy source, but even as H (D) atoms source (the internal pressure for H is lower than the internal pressure for He bubbles) contributing to Ostwald ripening for the ‘large’ bubbles. For the ‘small’ bubbles, this contribution is, probably, reduced; this fact could explain the difference in rB values. The cracks induced by H irradiation around the He bubbles [7] could also play a role in the coarsening phenomenon. We can conclude, for our analyzed cases, there is only one coarsening mechanism for ‘small’ and for ‘large’ bubbles: the Ostwald ripening, the difference in rB values being due to the different H contribution, which is even smaller in matrix than
Fig. 6. Helium bubbles at dislocations, 300 appm, 100 h annealing.
Fig. 5. Helium bubbles in the vicinity of grain boundaries, 300 appm, 100 h annealing.
in grain boundaries, is sufficient to transform the migration and coalescence coarsening mechanism in the bulk into an Ostwald ripening mechanism by the created vacancy sources. To verify our conclusions on hydrogen influence, we intend to analyze, in the same H (D) irradiation and annealing conditions, 1000 appm He specimens (where we expect to observe a migration and coalescence coarsening mechanism for the small bubbles in the matrix) and also to use an annealing temperature below 773 K, when He mobility is strongly reduced. Obviously, our results suggest that for the real case of the nuclear fusion reactor, the effects of hydrogen isotopes and helium irradiation on first wall materials are very important and their synergetic behavior could be essentially different from the present experiments where H and He are separately implanted.
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Project RUM 056.2. The authors are very grateful to Prof. H. Ullmaier and his team from IFF-KFA Julich for specimen He-implantation and annealing.
References
.
Fig. 7. ‘Clustering’ phenomenon, 100 appm, 1000 h annealing.
Acknowledgements This Work was supported in part by the BMFT (Germany)-IAP (Romania) bilateral agreement,
[1] V. Chernikov, H. Trinkaus, P. Jung, H. Ullmaier, The formation of helium bubbles near the surface and in the bulk in nickel during post-implantation annealing, J. Nucl. Mater. 170 (1990) 31. [2] M. Myers, W.R. Wampler, Trapping of hydrogen in ion-implanted metals, J. Nucl. Mater. 111 – 112 (1982) 579. [3] J. Rothaut, H. Schroeder, H. Ullmaier, Studies on He bubbles and their size distribution in nickel, Philos. Mag. A47 (1983) 781. [4] B. Constantinescu, S. Dima, V. Florescu, E. Ivanov, D. Plostinaru, C. Sarbu, Use of 4.7 MeV a-particles in elemental analysis and fusion reactor material studies, Nucl. Instr. Meth. B16 (1986) 488. [5] W. Qiang-Li, W. Kesternich, H. Schroeder, D. Schwahn, H. Ullmaier, Gas densities in helium bubbles in nickel measured by small angle neutron scattering. Acta Metall. Mater. 38 (12) (1990) 2383. [6] M. Myers, D.M. Follstaedt, F. Besenbacher, J. Bootiger, Defect trapping of ion-implanted deuterium in nickel, J. Appl. Phys. 53 (1982) 8734. [7] G. Solovioff, E. Abramov, D. Eliezer, The formation of H induced blisters and their growth in nickel pre-implanted with He, J. Nucl. Mater. 217 (1994) 287. [8] V. Kirsanov, M.V. Musina, V.V. Rybin, The influence of H on formation of He vacancy voids in metals, J. Nucl. Mater. 191 – 194 (1992) 1318.
Radiation damage studies on Ni implanted with high energy He and D ions B. Constantinescu *, F. Vasiliu, G. Alexandru Institute of Atomic Physics, POB MO-6, Bucharest, Romania
Abstract The behavior of hydrogen isotopes in metals is very important for the future nuclear fusion reactor. To study deuterium influence on helium pre-irradiated nickel, 0 – 28 MeV He + + and 7 MeV D + beams were used. Thirty, 100 and 300 appm He pre-implanted samples were D + (1018 ions per cm2) irradiated and 1, 10, 100 and 1000 h high vacuum annealed (1273 K). After an electrochemical preparation (Struers jet), they were examined by transmission electron microscopy (TEM). Values for He bubbles’ radii and densities depending on He ions’ doses and annealing periods are reported. Two types of bubbles were observed: ‘small’ bubbles, predominantly in the matrix (from 5 nm radius for 30 appm, 1 h annealing to 35 nm for 300 appm, 100 h annealing) and ‘large’ bubbles, predominantly in the grain boundaries regions, but even in some dislocations (from 30 nm radius for 30 appm, 1 h annealing to 120 nm for 300 appm, 100 h annealing). A unique bubble coarsening mechanism, the Ostwald ripening, is considered. The influence of deuterium on the ‘small’ and ‘large’ bubbles’ radii values is discussed. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction During the last few years, the behavior of helium in metals has gained considerable interest, because it can cause embrittlement and other materials degradation in components of advanced future nuclear energy systems (fast fission and fusion reactors). Most of these effects are caused by the nucleation and growth of helium bubbles which inevitably form at elevated temperature because of the vanishingly small solubility of helium in solids.
* Corresponding author.
Although there is wide agreement upon the principal mechanism leading to helium-induced changes of materials’ properties, evidently a quantitative understanding of these processes requires a solid knowledge about the basic properties of helium in metals. Among others, the density and size distributions of bubbles as a function of helium content, temperature and time of annealing are of particular interest [1]. The first wall of fusion reactor is also subject to high hydrogen ion and atom fluxes. It has been assumed that due to the higher diffusivity and release rate of hydrogen than those of helium in most candidate materials, the effect of hydrogen is minimal. However, the role of hydrogen for mi-
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00209-9
80
B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
crostructural changes, such as void swelling, has not been extensively studied. It is established that hydrogen may be trapped at particular defect sites in metals [2]. The purpose of the present study is to determine combined helium-hydrogen effects as trapping of hydrogen around or near helium bubbles and the influence on size distributions of bubbles as a function of helium content and periods of annealing at 1273 K.
2. Experimental Nickel foils (99.995% pure) of 100 mm thickness were annealed at 1373 K for 2 h in a vacuum greater than 10 − 5 Pa. Homogeneous helium implantation at room temperature was achieved by varying the range of the 28 MeV a-beam of the KFA-Julich (Germany) compact cyclotron by a wheel that continuously rotated 50 Al foils of different thickness through the beam [3]. Samples with nominal helium concentrations of 30, 100 and 300 appm were obtained. Subsequently, these samples were deuterium (1018 D + 7 MeV ions cm − 2) at room temperature irradiated by the Bucharest U-120 classical cyclotron [4]. Then, the samples were annealed at 1273 K for 1, 10, 100 and 1000 h in a vacuum. From each of the helium+ deuterium implanted specimen areas, 3 mm disks were punched out. The disks were electrochemically thinned by jet polishing using a TENUPOL STRUERS JET apparatus and two chemical solutions: perchloric acid plus ethanol at 0°C and sulfuric acid plus glycerin at 10°C. The specimens were investigated in a JEOL TEMSCAN 200 CX microscope operated at 200 kV and in a TESLA BS 240 microscope operated at 120 kV. Most of the micrographs were taken in phase contrast under defocusing condition rB and were determined from histograms obtained with a semiautomatic particle size analyzer and, partially, by direct observation, with an uncertainty of at most 9 30%. For the evaluation of bubble densities, CB, the foil thickness determination was made by interference fringes observation which introduces an uncertainty of about 950%.
3. Results and discussion The annealing behavior of helium bubbles forming in nickel after helium implantation at room temperature which is discussed in details in Chernikov et al. and Qiang-Li et al. [1,5] seems to represent a striking example for the effect of the internal pressure on bubble coarsening [6]. So, for annealing temperature above 900 K and high He concentrations (500–5000 appm) the coarsening rate is found to be substantially faster close to the surface of the sample than in the bulk but comparable to the coarsening rate at low He concentrations (5 200 appm). Accordingly, two distinct coarsening branches in an Arrhenius plot of average bubble radii were identified: a weakly activated (rB values from 0.6 at 800 K to 2 nm at 1400 K) one for slow bubble coarsening in the bulk, and a highly activated (rB values from 1 at 1000 K to 800 nm at 1400 K) one for fast bubble coarsening close to the surface (or in the grain
Fig. 1. Mean radius rB of helium bubbles as a function of the He ions doses.
B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
boundaries). This difference may be correlated with differences in the pressure within the bubbles: higher pressure with increasing He concentration in the bulk but a relaxation of an initially high pressure within bubbles sufficiently close to surface (or grain boundaries) due to vacancies provided by the sample surface (or by internal radiation damages). Consequently, the weakly activated branch (slow coarsening) may be attributed to bubbles with high internal pressure which can coarsen by migration and coalescence while Ostwald ripening is completely suppressed. The highly activated branch (fast coarsening) may be attributed to bubbles in which pressure is low or relaxes during the annealing from an initially high to a finally low value. Such bubbles can coarsen by Ostwald ripening which seems to surpass its maximum rate when the pressure relaxes by vacancies originating from implantation damage (bulk bubbles for low He concentrations and grain boundaries bubbles for high He concentrations) or from the surface. Our results are presented in Figs. 1 – 3 (unfortunately, there are some missing points, because some specimens were damaged during thinning). Apparently, there are two categories of bubbles: ‘small’ in bulk (matrix) bubbles (Fig. 4) and ‘large’ (grain boundaries and dislocations) bubbles (Figs. 5 and 6). Evidently, it is a conventional classification, the essential difference being the affiliation of ‘small’ bubbles strictly to matrix and of ‘large’ bubbles strictly to grain boundaries and dislocations. Critical sizes (Fig. 1) to separate them are 30 nm for 1, 10 and 100 h annealing periods and 100 nm for 1000 h annealing period, for all He concentration values. The rB values for small bubbles (6 – 30 nm) are much larger than the values reported in [1] for the same type of bubbles in the case of simple He implantation (1.5 nm for 1273 K), so, we could assume an Ostwald ripening coarsening mechanism via helium, hydrogen (deuterium) and vacancy resolution and reabsorption. Probably, the relaxation of initially over pressurized He bubbles by annealing of the associated He+H (D) dislocation network is quite substantial. As concerning ‘large’ bubbles, our values are slightly larger than in Chernikov et al. [1], the Ostwald ripening being
81
Fig. 2. Mean radius rB of helium bubbles as a function of the annealing periods.
evident. Variations in the implanted helium concentrations (from 30 to 300 appm) have relatively little influence on the mean radius. However, we must find and explain the influence of hydrogen (deuterium) on our data as compared to a simple helium implantation case reported for nickel in Chernikov et al. and Qiang-Li et al. [1,5]. It is assumed that trapped H isotopes could play a role in the triggering of fast Ostwald ripening. In Myers et al. [6], there is an attempt to explain the trapping of H around He bubbles and relate it to a chemisorption-like interaction at the isolated bubbles. In Solovioff et al. [7] a cracking phenomenon generated by hydrogen in the grain boundaries of the nickel, as a result of the greater stress on the material due to the hydride formation is reported. In Kirsanov et al. [8] the (He+ H+ 2V) and (He+ H+ V) clusters are investigated to determine hydrogen influence on the process of helium-vacancy void formation. However, a detailed and qualitative model which
82
B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
can help to understand these effects and to estimate the trapping binding energy has not been established. An exception seems to be the 1000-h annealing period data, where a ‘clustering’ phenomenon (Fig. 7) is observed. The appearance of such structures of very large bubbles cannot be explained for the moment. Probably, during this long annealing period an unusual concentration of defects facilitates this very enhanced bubbles coarsening. We could mention that even for 300 appm, 100-h annealing period case, small ‘clusters’ (2–3–4 ‘small’ bubbles in the bulk) were observed. Concerning small bubbles’ volume densities versus annealing periods (Fig. 3), between 1 and 100 h a relatively constant value for all He doses was observed (with only a significant decrease for 300 appm for 100 h, where isolated ‘clusters’ were reported). For 1000 h, due to the strong ‘clustering’ phenomenon above mentioned, the densities
Fig. 4. Helium bubbles in the matrix; 300 appm, 100 h annealing.
values are two orders of magnitude lower (from 1021 to 1019 m − 3).
4. Conclusion
Fig. 3. Volume density of ‘small’ bubbles as a function of the annealing periods.
Concerning possible bubbles’ coarsening mechanisms, from Chernikov et al. [1] results for He concentration values are similar to those of this study, but in the absence of D implantation, matrix bubbles (diameter values less than 1 nm) can coarsen by migration and coalescence of He atoms and vacancies, moderately reduced by the observed high internal pressure, while Ostwald ripening is completely suppressed. This one is observed for grain boundaries’ bubbles in which the pressure is low or relaxes during annealing mainly due to surface vacancies. In our cases, the large diameter values for matrix bubbles (\ 5 nm) exclude high internal pressure for 30–300 appm
B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
83
He concentration values and, consequently, the migration and coalescence mechanism, and suggest even for matrix bubbles the Ostwald ripening mechanism. So, we could assume a relatively important role of hydrogen isotopes trapped in grain boundaries as active vacancy source, but even as H (D) atoms source (the internal pressure for H is lower than the internal pressure for He bubbles) contributing to Ostwald ripening for the ‘large’ bubbles. For the ‘small’ bubbles, this contribution is, probably, reduced; this fact could explain the difference in rB values. The cracks induced by H irradiation around the He bubbles [7] could also play a role in the coarsening phenomenon. We can conclude, for our analyzed cases, there is only one coarsening mechanism for ‘small’ and for ‘large’ bubbles: the Ostwald ripening, the difference in rB values being due to the different H contribution, which is even smaller in matrix than
Fig. 6. Helium bubbles at dislocations, 300 appm, 100 h annealing.
Fig. 5. Helium bubbles in the vicinity of grain boundaries, 300 appm, 100 h annealing.
in grain boundaries, is sufficient to transform the migration and coalescence coarsening mechanism in the bulk into an Ostwald ripening mechanism by the created vacancy sources. To verify our conclusions on hydrogen influence, we intend to analyze, in the same H (D) irradiation and annealing conditions, 1000 appm He specimens (where we expect to observe a migration and coalescence coarsening mechanism for the small bubbles in the matrix) and also to use an annealing temperature below 773 K, when He mobility is strongly reduced. Obviously, our results suggest that for the real case of the nuclear fusion reactor, the effects of hydrogen isotopes and helium irradiation on first wall materials are very important and their synergetic behavior could be essentially different from the present experiments where H and He are separately implanted.
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B. Constantinescu et al. / Fusion Engineering and Design 41 (1998) 79–84
Project RUM 056.2. The authors are very grateful to Prof. H. Ullmaier and his team from IFF-KFA Julich for specimen He-implantation and annealing.
References
.
Fig. 7. ‘Clustering’ phenomenon, 100 appm, 1000 h annealing.
Acknowledgements This Work was supported in part by the BMFT (Germany)-IAP (Romania) bilateral agreement,
[1] V. Chernikov, H. Trinkaus, P. Jung, H. Ullmaier, The formation of helium bubbles near the surface and in the bulk in nickel during post-implantation annealing, J. Nucl. Mater. 170 (1990) 31. [2] M. Myers, W.R. Wampler, Trapping of hydrogen in ion-implanted metals, J. Nucl. Mater. 111 – 112 (1982) 579. [3] J. Rothaut, H. Schroeder, H. Ullmaier, Studies on He bubbles and their size distribution in nickel, Philos. Mag. A47 (1983) 781. [4] B. Constantinescu, S. Dima, V. Florescu, E. Ivanov, D. Plostinaru, C. Sarbu, Use of 4.7 MeV a-particles in elemental analysis and fusion reactor material studies, Nucl. Instr. Meth. B16 (1986) 488. [5] W. Qiang-Li, W. Kesternich, H. Schroeder, D. Schwahn, H. Ullmaier, Gas densities in helium bubbles in nickel measured by small angle neutron scattering. Acta Metall. Mater. 38 (12) (1990) 2383. [6] M. Myers, D.M. Follstaedt, F. Besenbacher, J. Bootiger, Defect trapping of ion-implanted deuterium in nickel, J. Appl. Phys. 53 (1982) 8734. [7] G. Solovioff, E. Abramov, D. Eliezer, The formation of H induced blisters and their growth in nickel pre-implanted with He, J. Nucl. Mater. 217 (1994) 287. [8] V. Kirsanov, M.V. Musina, V.V. Rybin, The influence of H on formation of He vacancy voids in metals, J. Nucl. Mater. 191 – 194 (1992) 1318.