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The temperature dependence of the flow stress of 600-MEV proton irradiated aluminium
Journal
992
of Nuclear
Materials
155- 157 (198X) 992.-995
North-Holland,
THE TEMPERATURE DEPENDENCE IRRADIATED ALUMINIUM D. GAVILLET, Eidgenissisches
M. VICTORIA
OF 600-MEV
PROTON
and W.V. GREEN
Institut fir Reaktor/orschung
R. GOTTHARDT
OF THE FLOW STRESS
Amsterdam
(EIR),
5303 Wiirenlingen,
Switzerland
and J.L. MARTIN
Instrtut de G&tie Atomique, Ecole Polytechnique Fkdb-ale de Lausanne (EPFL), 1015 Luusanne, Switzerland Tensile tests were performed on aluminium foils of 0.1 mm thickness that had been irradiated in the PIREX facility in the cyclotron of the Swiss Nuclear Research Institute (SIN) at doses between 0.9 to 5 dpa. Helium is produced at a measured rate of 230 appm/dpa simultaneously with the displacement damage. The post irradiation tests were performed in the range from 190 to 470 K. An increase of a factor four in the flow stress is found in the irradiated material at a dose 4.1 dpa at 190 K. The increase in flow stress is found to be proportional to the square root of the dose at all test temperatures. This increase has no clear correlation with bubble structure observed by TEM (either with bubble size or number density). These measurements, together with those of activation volume and TEM in-situ deformation, indicate that the main obstacle to dislocation glide is the presence of a dispersion of small ( - 1 nm diameter) clusters of impurities produced by spallation reactions during the irradiation. A modified F’leischer hardening model is used to describe the results. Good agreement with experimental data is found for a to the angle measured during the TEM in-situ deformations. dislocation escape of 140 ‘, which corresponds
1. Introduction In a fusion reactor, first wall materials have to sustain the compounded effects of displacement damage and impurities produced by the energetic neutrons. One of the results produced on the microstructure is well known: vacancies, helium and hydrogen generated under these conditions give rise to the formation of voids and gas filled bubbles. Other impurities beside the gaseous ones will produced by the fusion neutrons. Although they are generated in small amounts, the fact that they might eventually stabilize elements of the microstructure such as collapsed cascades or interstitial loops, could lead to their playing an important role in determining macroscopic properties, such as the flow stress. Impurities other than the gaseous ones are produced in metals irradiated with medium energy protons [1,2], where irradiation conditions in the appropriate range of temperatures produce a distribution of helium filled bubbles [3]. The influence of different bubble distributions on the mechanical properties can then be studied and compared to the effects produced by the other impurities in the same irradiated specimens. Furthermore, as shown in ref. [3] in the case of aluminium, by irradiating at sufficiently low temperatures, substantial variations in the displacement dose (and therefore in the total amount of impurities produced) can be obtained with little or no change in the bubble structure. This facilitates the separation of effects due to bubbles and those due to the displacement damage or the impurities. In the present paper results are presented on the mechanical properties of pure aluminium irradiated with 600-MeV protons, in an effort to study the different 0022-3115/88/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
hardening components. The results of an earlier paper [4] are reanalyzed in terms of a hardening model that takes into account all of these results.
2. Experimental procedures High purity (99.9999%) aluminium foils of 0.125 mm thickness were irradiated in the PIREX facility installed in the 600-MeV proton accelerator of the Swiss Institute for Nuclear Research (SIN). The details of the installation have been described before [2]. Proton beams in the range from 120 to 150 PA at current densities between 3.5 and 14.6 PA/mm’ were used. Total displacement dose ranged between 0.7 and 5 dpa at irradiation temperatures between 400 and 750 K. The average grain size in the aluminium specimens is between 110 and 160 I-Lm. Tensile specimens with an elliptically shaped reduced gage section were cut from the irradiated foils in such a way that they were centered on the irradiated spot [4,5]. The deformation was done with a soft tensile micromachine especially designed to test thin radioactive specimens [4]. The strain rate used was 1.5 X lop5 s--l. Deformation temperatures between 190 and 470 K were obtained by using a cooled methanol solution for temperature below room temperature and an electrical resistance furnace for those in the region from 295 to 470 K. Temperature control was within 1 K [5]. The flow stress was determined graphically. The values given in table 1 and on the figures corresponded to the stress at a plastic deformation of 0.1%. For the microscope observations, the whole specimen was mounted with conducting glue on the scanning
D. Gavillet et al. / Temperature dependence
oftheflow
stress
ofirradiatedAI
993
electron microscope stage at the end of deformation. A 3 mm diameter disc was punched out at the center of the deformed region and thinned down in a 20% perchloric acid-ethanol electrolytic solution. Transmission electron microscope observations were performed in a Phillips EM 300 microscope.
3. Experimental results An increase in yield strength of the irradiated aluminium is generally observed. The shape of the tensile curve is similar for all irradiation conditions and testing temperatures. Typical examples at three different testing temperatures are shown in fig. 1 for specimens irradiated to 1 dpa. Only the initial 1.2% elongation of the deformation curve is shown. No sharp yield point is observed. After approximately 0.4% deformation, a region of low hardening sets in up to fracture. The results of the mechanical testing are given in table 1. Those shown for the bubble structures are the ones measured after deformation. They are equal to those measured on specimens with identical irradiation conditions and no deformation [3], so the bubble structure in the grain interior is not modified under tensile testing. The values of the flow stress normalized by the shear modulus are plotted as a function of testing tempera-
_I 0.0
0.2
0.4
0.6 STRAIN
0.8
1.0
1.2
[%I
Fig. 1. Tensile curves to 1.2% strain at three testing temperatures of aluminium samples irradiated at 0.9 dpa.
ture for different weak temperature dose. On the other ent temperatures better to a square than to the linear
average doses in fig. 2. It shows a dependence, which increases with hand, the dose dependence at differis shown in fig. 3. It can be fitted root of the dose dependence rather dependence used in the earlier paper
141. No loss of ductility is observed in the specimens deformed at testing temperatures between 190 and 295 K. In fact, as shown in ref. [4], deformations of more than 25% elongation can be imposed on the foil speci-
Table 1 Results of mechanical testing SAMPLE No.
T,, (K)
Dose (dpa)
R, (nm)
_
AL 6N
84
530
0.9
69
730
0.9
82
480
1.7
56 94
500 750
85
2.24
N, (me3)
_
Ib a
Tdet
%(O.l%,
Rupture
(nm)
(K)
(MPa)
we
_
190 290 370 470 290 370 470 190 290 190 290 290 190 290 290 370 470 290 370 470 190 290 470
20.5 16.0 14.1 11.0 35.5 30.5 24.5 41.9 36.7 53.2 42.0 44.0 55.9 45.0 40.0 34.0 24.5 40.8 39.7 28.8 70.0 53.3 34.0
3.96 x lo*’
237
3.5 x 10’9
771
1.95
2.1 x10**
110
2.0 2.1
3.0 6.0
6 x10*’ 6.8 x10*0
167 350
530
2.2
4.16
2.21 x 1021
233
90
690
2.2
72
425
4.0
1.75
2.3 x10**
111
81
570
5.0
24.0
a The mean bubble spacing I, is: (Nb2Rb)-‘/*.
1.4
Transgranular
Transgranular
Intergranular
Intergranular
c10-'41 40 . +
Non lrradmted .6 < Dose <
e i
O/ 150
1.2 dpa
. l
I
7
200
250
300
350
Temperature
Fig. 2. Normalized flow stress versus nonirradiated and irradiated
400
450
500
5 50
CKI
testing temperature aluminium.
4. Discussion The present results confirm our earlier statement [4], that bubbles are not the controlling hardening agent in aluminium irradiated with 600-MeV protons. This can be rapidly visualized in table 1, by comparing results from specimens No. 82 and 72. Although they have
surface
after
fracture
2
3 Dose
in
mens in this range of temperature. The specimens deformed at 470 K on the other hand, failed at deformations of the order of 2% elongation. This loss of ductility is reflected in the failure mode as observed under the scanning electron microscope: the specimens deformed at low temperature show typical ductile transgranular failure, with grains in the gage region intensively deformed, fig. 4A. Those deformed at 470 K failed by intergranular fracture, fig. 4B, with little deformation in the grains apparent as slip lines in the surface.
Fig. 4. Sample
1
4
5
6
Cdpal
Fig. 3. Normalized flow stress versus irradiation dose in aluminium deformed at different temperatures. (Points are experimental values, lines are calculated values.)
approximately the same bubble structure, they differ in a factor 2.5 in the displacement dose. The flow stress is 25% larger for the larger dose. Irradiations with protons of this energy produce a number of impurities in aluminium. Apart from helium. which is produced at the measured rate of 230 appm/dpa, both Mg and Na are produced, at rates calculated [l] to be 143 appm/dpa and 49 appm/dpa, respectively. A part of the total Na produced is measured as the isotope 22Na with a production rate of 9.6 appm/dpa. As was shown in refs. [4] and [5], their strengthening effect in solid solution is not sufficient to explain the values observed after irradiation. The hypothesis has been advanced [5] that these results can be explained on the basis of a fine dispersion of clusters of submicroscopic size. These clusters can be formed either by the impurities or they can be interstitial loops stabi-
at 290 K and 470 K (A: Sample C = 1.2%).
84, Tder = 290 K, c = 22%; B: Sample
90, Tder = 470 K.
D. Gavillet et al. / Temperature dependence of the flow stress of irradiated AI
lized by the same impurities. Clusters of this type have been detected in low temperature irradiation of dilute alloys of aluminium with electrons (61 and fast neutrons [7]. Interstitial clusters have been detected in pure aluminum in which a cascade structure was produced by low temperature irradiation with fast neutrons [8]. In all these cases, the clusters anneal at low temperatures: Mg is said to lose its trapping capability between 100 and 180 K [6]. In the case of irradiations with 600-MeV protons it has been shown [9] that the appreciable initial change in resistivity with irradiation in pure aluminium is not changed by annealings at temperatures as high as 820 K, an indication that the microstructure produced is much more stable with this type of irradiation. Furthermore, in situ deformation observations in the electron microscope [lo], show that dislocations are effectively stopped at obstacles which can not be resolved. A model has been developed, based on a modification of the hardening model by Fleischer [ll]. The critical shear stress is given by [S] 7 = (fmax)3’2c1’2 E fib’l-“’
’
where r is the dislocation line tension, b its burger vector, c is the concentration of impurities and f,, corresponds to the maximum interaction force between the obstacle and the dislocation, at the moment it escapes the obstacle and is given by:
f,, = 2ra/2. Approximate values for the escapement angle a can be measured from the in-situ TEM deformation experiments and further adjusted for a best fit of the experimental data. The flow stress results are compared to the experimental data in fig. 3. The temperature dependence can be obtained in a first approximation by considering a parabolic force law between the obstacle and the dislocation [12]. It can be calculated to be [5]:
There is very good agreement with the experimental data. By using the value of 500b3 for the activation volume [4], an estimate can be made of the cluster size distribution: their number density is of the order of
995
1O23 me3 (and varies with the dose) with about 30 atoms per cluster. The observed loss of ductility is associated with a change in fracture mode. Although no detailed microstructural observations have been yet completed, initial observations of bubble structure at the grain boundaries indicate that it is probably associated with a change in bubble distribution in grain boundaries, as observed in stainless steel [13]. References [l] S.L. Green, J. Nucl. Mater. 126 (1984) 30. [2] W.V. Green, M.P. Victoria and S.L. Green, J. Nucl. Mater. 133 & 134 (1985) 58. (31 D. Gavillet, R. Gotthardt, J.L. Martin, S.L. Green, W.V. Green and M. Victoria, in: Proc. 12th Int. Symp. on Effects of Radiation on Materials, Williamsburg, 1984. Eds. F.A. Gamer and J.J. Perrin, ASTM STP 870 (1985) p. 394. [4] D. Gavillet, W.V. Green, M. Victoria and J.L. Martin, Int. Workshop on The Relation between Mechanical Properties and Microstructure under Fusion Irradiation Conditions, Eds. B.N. Singh, T. Leffers, M. Victoria and W.V. Green, Radiat. Eff. 101 (1987) 283. [5] D. Gavillet, Microstructure et proprietes mecaniques de l’aluminium irradie par des protons de 600 MeV, These No. 652, Ecole Polytechnique Fed&ale de Lausanne (1986). (61 F. Dworschak, Th. Monsau and H. Wollenberger, J. Phys. F6 (1976) 2207. [7] R. Rausch, A. Schmalzbauer, G. Wallner and J. Peisl, Mater. Sci. Forum 15-18 (1987) 587. [8] D. Grasse, B. v. Guerard and J. Peisl, Radiat. Eff. 66 (1982) 21. 191 F. Paschoud, R. Gotthardt and S.L. Green, in: Proc. 13th Int. Symp. on Radiation Induced Changes in Microstructure, Eds. F.A. Gardner, N.H. Packan and A.S. Kumar, ASTM STP 955 (1987). and DOI D. Gavillet, W.V. Green, M. Victoria, R. Gotthardt J.L. Martin, in: Proc. 13th Int. Symp. on Radiation Induced Changes in Microstructure, Eds. F.A. Gardner, N.H. Packan and A.S. Kumar, ASTM STP 955 (1987). 1111 R.L. Fleischer, Acta Metall. 11 (1963) 203. WI P. Haasen, Solution Hardening in fee Metals, Chap. 15 in: Dislocations in Solids, Ed. F.R. Nabarro (North-Holland Publishing Co., Amsterdam, 1979). 1131 H. Schroeder and P. Batfalsky, J. Nucl. Mater. 117 (1983) 287; 122 & 123 (1984) 1475.
992
of Nuclear
Materials
155- 157 (198X) 992.-995
North-Holland,
THE TEMPERATURE DEPENDENCE IRRADIATED ALUMINIUM D. GAVILLET, Eidgenissisches
M. VICTORIA
OF 600-MEV
PROTON
and W.V. GREEN
Institut fir Reaktor/orschung
R. GOTTHARDT
OF THE FLOW STRESS
Amsterdam
(EIR),
5303 Wiirenlingen,
Switzerland
and J.L. MARTIN
Instrtut de G&tie Atomique, Ecole Polytechnique Fkdb-ale de Lausanne (EPFL), 1015 Luusanne, Switzerland Tensile tests were performed on aluminium foils of 0.1 mm thickness that had been irradiated in the PIREX facility in the cyclotron of the Swiss Nuclear Research Institute (SIN) at doses between 0.9 to 5 dpa. Helium is produced at a measured rate of 230 appm/dpa simultaneously with the displacement damage. The post irradiation tests were performed in the range from 190 to 470 K. An increase of a factor four in the flow stress is found in the irradiated material at a dose 4.1 dpa at 190 K. The increase in flow stress is found to be proportional to the square root of the dose at all test temperatures. This increase has no clear correlation with bubble structure observed by TEM (either with bubble size or number density). These measurements, together with those of activation volume and TEM in-situ deformation, indicate that the main obstacle to dislocation glide is the presence of a dispersion of small ( - 1 nm diameter) clusters of impurities produced by spallation reactions during the irradiation. A modified F’leischer hardening model is used to describe the results. Good agreement with experimental data is found for a to the angle measured during the TEM in-situ deformations. dislocation escape of 140 ‘, which corresponds
1. Introduction In a fusion reactor, first wall materials have to sustain the compounded effects of displacement damage and impurities produced by the energetic neutrons. One of the results produced on the microstructure is well known: vacancies, helium and hydrogen generated under these conditions give rise to the formation of voids and gas filled bubbles. Other impurities beside the gaseous ones will produced by the fusion neutrons. Although they are generated in small amounts, the fact that they might eventually stabilize elements of the microstructure such as collapsed cascades or interstitial loops, could lead to their playing an important role in determining macroscopic properties, such as the flow stress. Impurities other than the gaseous ones are produced in metals irradiated with medium energy protons [1,2], where irradiation conditions in the appropriate range of temperatures produce a distribution of helium filled bubbles [3]. The influence of different bubble distributions on the mechanical properties can then be studied and compared to the effects produced by the other impurities in the same irradiated specimens. Furthermore, as shown in ref. [3] in the case of aluminium, by irradiating at sufficiently low temperatures, substantial variations in the displacement dose (and therefore in the total amount of impurities produced) can be obtained with little or no change in the bubble structure. This facilitates the separation of effects due to bubbles and those due to the displacement damage or the impurities. In the present paper results are presented on the mechanical properties of pure aluminium irradiated with 600-MeV protons, in an effort to study the different 0022-3115/88/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
hardening components. The results of an earlier paper [4] are reanalyzed in terms of a hardening model that takes into account all of these results.
2. Experimental procedures High purity (99.9999%) aluminium foils of 0.125 mm thickness were irradiated in the PIREX facility installed in the 600-MeV proton accelerator of the Swiss Institute for Nuclear Research (SIN). The details of the installation have been described before [2]. Proton beams in the range from 120 to 150 PA at current densities between 3.5 and 14.6 PA/mm’ were used. Total displacement dose ranged between 0.7 and 5 dpa at irradiation temperatures between 400 and 750 K. The average grain size in the aluminium specimens is between 110 and 160 I-Lm. Tensile specimens with an elliptically shaped reduced gage section were cut from the irradiated foils in such a way that they were centered on the irradiated spot [4,5]. The deformation was done with a soft tensile micromachine especially designed to test thin radioactive specimens [4]. The strain rate used was 1.5 X lop5 s--l. Deformation temperatures between 190 and 470 K were obtained by using a cooled methanol solution for temperature below room temperature and an electrical resistance furnace for those in the region from 295 to 470 K. Temperature control was within 1 K [5]. The flow stress was determined graphically. The values given in table 1 and on the figures corresponded to the stress at a plastic deformation of 0.1%. For the microscope observations, the whole specimen was mounted with conducting glue on the scanning
D. Gavillet et al. / Temperature dependence
oftheflow
stress
ofirradiatedAI
993
electron microscope stage at the end of deformation. A 3 mm diameter disc was punched out at the center of the deformed region and thinned down in a 20% perchloric acid-ethanol electrolytic solution. Transmission electron microscope observations were performed in a Phillips EM 300 microscope.
3. Experimental results An increase in yield strength of the irradiated aluminium is generally observed. The shape of the tensile curve is similar for all irradiation conditions and testing temperatures. Typical examples at three different testing temperatures are shown in fig. 1 for specimens irradiated to 1 dpa. Only the initial 1.2% elongation of the deformation curve is shown. No sharp yield point is observed. After approximately 0.4% deformation, a region of low hardening sets in up to fracture. The results of the mechanical testing are given in table 1. Those shown for the bubble structures are the ones measured after deformation. They are equal to those measured on specimens with identical irradiation conditions and no deformation [3], so the bubble structure in the grain interior is not modified under tensile testing. The values of the flow stress normalized by the shear modulus are plotted as a function of testing tempera-
_I 0.0
0.2
0.4
0.6 STRAIN
0.8
1.0
1.2
[%I
Fig. 1. Tensile curves to 1.2% strain at three testing temperatures of aluminium samples irradiated at 0.9 dpa.
ture for different weak temperature dose. On the other ent temperatures better to a square than to the linear
average doses in fig. 2. It shows a dependence, which increases with hand, the dose dependence at differis shown in fig. 3. It can be fitted root of the dose dependence rather dependence used in the earlier paper
141. No loss of ductility is observed in the specimens deformed at testing temperatures between 190 and 295 K. In fact, as shown in ref. [4], deformations of more than 25% elongation can be imposed on the foil speci-
Table 1 Results of mechanical testing SAMPLE No.
T,, (K)
Dose (dpa)
R, (nm)
_
AL 6N
84
530
0.9
69
730
0.9
82
480
1.7
56 94
500 750
85
2.24
N, (me3)
_
Ib a
Tdet
%(O.l%,
Rupture
(nm)
(K)
(MPa)
we
_
190 290 370 470 290 370 470 190 290 190 290 290 190 290 290 370 470 290 370 470 190 290 470
20.5 16.0 14.1 11.0 35.5 30.5 24.5 41.9 36.7 53.2 42.0 44.0 55.9 45.0 40.0 34.0 24.5 40.8 39.7 28.8 70.0 53.3 34.0
3.96 x lo*’
237
3.5 x 10’9
771
1.95
2.1 x10**
110
2.0 2.1
3.0 6.0
6 x10*’ 6.8 x10*0
167 350
530
2.2
4.16
2.21 x 1021
233
90
690
2.2
72
425
4.0
1.75
2.3 x10**
111
81
570
5.0
24.0
a The mean bubble spacing I, is: (Nb2Rb)-‘/*.
1.4
Transgranular
Transgranular
Intergranular
Intergranular
c10-'41 40 . +
Non lrradmted .6 < Dose <
e i
O/ 150
1.2 dpa
. l
I
7
200
250
300
350
Temperature
Fig. 2. Normalized flow stress versus nonirradiated and irradiated
400
450
500
5 50
CKI
testing temperature aluminium.
4. Discussion The present results confirm our earlier statement [4], that bubbles are not the controlling hardening agent in aluminium irradiated with 600-MeV protons. This can be rapidly visualized in table 1, by comparing results from specimens No. 82 and 72. Although they have
surface
after
fracture
2
3 Dose
in
mens in this range of temperature. The specimens deformed at 470 K on the other hand, failed at deformations of the order of 2% elongation. This loss of ductility is reflected in the failure mode as observed under the scanning electron microscope: the specimens deformed at low temperature show typical ductile transgranular failure, with grains in the gage region intensively deformed, fig. 4A. Those deformed at 470 K failed by intergranular fracture, fig. 4B, with little deformation in the grains apparent as slip lines in the surface.
Fig. 4. Sample
1
4
5
6
Cdpal
Fig. 3. Normalized flow stress versus irradiation dose in aluminium deformed at different temperatures. (Points are experimental values, lines are calculated values.)
approximately the same bubble structure, they differ in a factor 2.5 in the displacement dose. The flow stress is 25% larger for the larger dose. Irradiations with protons of this energy produce a number of impurities in aluminium. Apart from helium. which is produced at the measured rate of 230 appm/dpa, both Mg and Na are produced, at rates calculated [l] to be 143 appm/dpa and 49 appm/dpa, respectively. A part of the total Na produced is measured as the isotope 22Na with a production rate of 9.6 appm/dpa. As was shown in refs. [4] and [5], their strengthening effect in solid solution is not sufficient to explain the values observed after irradiation. The hypothesis has been advanced [5] that these results can be explained on the basis of a fine dispersion of clusters of submicroscopic size. These clusters can be formed either by the impurities or they can be interstitial loops stabi-
at 290 K and 470 K (A: Sample C = 1.2%).
84, Tder = 290 K, c = 22%; B: Sample
90, Tder = 470 K.
D. Gavillet et al. / Temperature dependence of the flow stress of irradiated AI
lized by the same impurities. Clusters of this type have been detected in low temperature irradiation of dilute alloys of aluminium with electrons (61 and fast neutrons [7]. Interstitial clusters have been detected in pure aluminum in which a cascade structure was produced by low temperature irradiation with fast neutrons [8]. In all these cases, the clusters anneal at low temperatures: Mg is said to lose its trapping capability between 100 and 180 K [6]. In the case of irradiations with 600-MeV protons it has been shown [9] that the appreciable initial change in resistivity with irradiation in pure aluminium is not changed by annealings at temperatures as high as 820 K, an indication that the microstructure produced is much more stable with this type of irradiation. Furthermore, in situ deformation observations in the electron microscope [lo], show that dislocations are effectively stopped at obstacles which can not be resolved. A model has been developed, based on a modification of the hardening model by Fleischer [ll]. The critical shear stress is given by [S] 7 = (fmax)3’2c1’2 E fib’l-“’
’
where r is the dislocation line tension, b its burger vector, c is the concentration of impurities and f,, corresponds to the maximum interaction force between the obstacle and the dislocation, at the moment it escapes the obstacle and is given by:
f,, = 2ra/2. Approximate values for the escapement angle a can be measured from the in-situ TEM deformation experiments and further adjusted for a best fit of the experimental data. The flow stress results are compared to the experimental data in fig. 3. The temperature dependence can be obtained in a first approximation by considering a parabolic force law between the obstacle and the dislocation [12]. It can be calculated to be [5]:
There is very good agreement with the experimental data. By using the value of 500b3 for the activation volume [4], an estimate can be made of the cluster size distribution: their number density is of the order of
995
1O23 me3 (and varies with the dose) with about 30 atoms per cluster. The observed loss of ductility is associated with a change in fracture mode. Although no detailed microstructural observations have been yet completed, initial observations of bubble structure at the grain boundaries indicate that it is probably associated with a change in bubble distribution in grain boundaries, as observed in stainless steel [13]. References [l] S.L. Green, J. Nucl. Mater. 126 (1984) 30. [2] W.V. Green, M.P. Victoria and S.L. Green, J. Nucl. Mater. 133 & 134 (1985) 58. (31 D. Gavillet, R. Gotthardt, J.L. Martin, S.L. Green, W.V. Green and M. Victoria, in: Proc. 12th Int. Symp. on Effects of Radiation on Materials, Williamsburg, 1984. Eds. F.A. Gamer and J.J. Perrin, ASTM STP 870 (1985) p. 394. [4] D. Gavillet, W.V. Green, M. Victoria and J.L. Martin, Int. Workshop on The Relation between Mechanical Properties and Microstructure under Fusion Irradiation Conditions, Eds. B.N. Singh, T. Leffers, M. Victoria and W.V. Green, Radiat. Eff. 101 (1987) 283. [5] D. Gavillet, Microstructure et proprietes mecaniques de l’aluminium irradie par des protons de 600 MeV, These No. 652, Ecole Polytechnique Fed&ale de Lausanne (1986). (61 F. Dworschak, Th. Monsau and H. Wollenberger, J. Phys. F6 (1976) 2207. [7] R. Rausch, A. Schmalzbauer, G. Wallner and J. Peisl, Mater. Sci. Forum 15-18 (1987) 587. [8] D. Grasse, B. v. Guerard and J. Peisl, Radiat. Eff. 66 (1982) 21. 191 F. Paschoud, R. Gotthardt and S.L. Green, in: Proc. 13th Int. Symp. on Radiation Induced Changes in Microstructure, Eds. F.A. Gardner, N.H. Packan and A.S. Kumar, ASTM STP 955 (1987). and DOI D. Gavillet, W.V. Green, M. Victoria, R. Gotthardt J.L. Martin, in: Proc. 13th Int. Symp. on Radiation Induced Changes in Microstructure, Eds. F.A. Gardner, N.H. Packan and A.S. Kumar, ASTM STP 955 (1987). 1111 R.L. Fleischer, Acta Metall. 11 (1963) 203. WI P. Haasen, Solution Hardening in fee Metals, Chap. 15 in: Dislocations in Solids, Ed. F.R. Nabarro (North-Holland Publishing Co., Amsterdam, 1979). 1131 H. Schroeder and P. Batfalsky, J. Nucl. Mater. 117 (1983) 287; 122 & 123 (1984) 1475.