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The recovery of structural defects in tungsten after irradiation and after cold work
Journal of Nuclear Materials 69 & 70 (1978) 0 North-Holland Publishing Company
THE RECOVERY
704-707
OF STRUCTURAL
DEFECTS IN TUNGSTEN AFTER IRRADIATION
AND
AFTER COLD WORK
J. CORNELIS, L. STALS *, P. DE MEESTER +, J. ROGGEN ** and J. NIHOUL ” Materials Science Department,
SCK/CEN,
B-2400 MOL, Belgium
1. Introduction
tungsten, these peaks are surpassed by the important stage III recovery. If one compares the spectra after reactor neutron irradiation with those after fission neutron irradiation for equal amounts of stage III recovery, it turns out that the additional transmutation impurities do not influence stage III recovery nor do they influence the high temperature part of stage II recovery, although the total impurity level due to transmutation reactions has increased by about two orders of magnitude. The impurity level thus approaches values of about 20 ppm which is of the same order of magnitude as the total concentration of intrinsic defects annealing in stage II and stage III. It is interesting to compare the recovery spectra following fission neutron irradiation with those fol-
The present paper reports on a resistometric study of the isochronal and isothermal recovery of tungsten in the temperature range 300-900 K. Tungsten wires of 0.1 mm dia. were drawn from an electron beam refined single crystal with a resistivity ratio of >30 000 from Westinghouse Electric Corporation. The resistivity ratio of fully annealed wires lies between 1000 and 1600. These cold-worked wires were subjected to isochronal and isothermal annealing treatments between 300 and 900 K. Furthermore, the isochronal and isothermal recovery of annealed and subsequently irradiated specimens has been studied in the same temperature range. Various types of irradiations were applied: 10 MeV electrons, fast neutrons (fission spectrum of uranium) and reactor neutrons (BR2 spectrum).
__ 2. Experimental
2opy--
data and discussion
Figs. l-4 show.the recovery spectra of tungsten in the temperature range 300-900 K following coldwork (fig. l), reactor neutron irradiation (fig. 2) fission neutron irradiation (fig. 3) and 10 MeV electron irradiation (fig. 4). Stage III occurs between 600 and 850 K in agreement with earlier published data [l-5]. With the exception for cold-worked tungsten, the spectra show some small first order peaks belonging to stage II. In the case of cold-worked * Materials Physics Group, Limburgs Universitair Centrum, Diepenbeek, Belgium. ** IIKW bursar at Katholieke Universiteit Leuven, Laboratorium voor Vaste Stof Fysika en Magnetisme. + Departement Metaalkunde, Katholieke Universiteit Leuven ++ Also Katholieke Universiteit Leuven.
400
Fig. 1. Recovery
704
600
of tungsten
600
following
T(K)-cold-work.
J. Come& et al. /Recovery ofst~u~tu~a~defects in tungsten
_‘X
i
H $b
21
E
0
705
1A&(nQcm) 4.26
a* 4
l.!
Old,
400 600 800 TWFig. 2. Recovery of tungsten following reactor neutron irradiation. Fig. 4. Recovery of tungsten following 10 MeV electron irradiation.
--T(K) qlo
30
790
650
6
10-i
1.2
1.3
1.6
1.6 -$$3,-t,
0 400
600
800 (HI-
Fig. 3. Recovery of tungsten following fission neutron irradiation (fission spectrum of uranium).
-
,
Fig. 5. Plot of A#’ versus I/T:*I for tungsten. l 10 MeV electron irradiation; 0 fission neutron irradiation; . reactor irradiation; n cold-work.
106
J. Cornelis et al. /Recovery -TlKl
r
uo
8.
1.85
.I’.
500
SF0
. t d 1.90
195
2130 i$T'10-3K"~ 1
Fig. 6. Plot of A$’ versus l/T!” for molybdenum. q V 2-2.5 MeV electron irradiation [ 8,9] ; e 10 MeV electron irradiation; o fission neutron irradiation.
lowing 10 MeV electron irradiation. In both cases the total impurity level has in fact not changed by the irradiation. Less substructure in stage II following electron irradiation is observed. Furthermore, although the general appearance of stage III looks the same in both cases, there is, however, a remarkable difference in the recovery kinetics. This is clearly demonstrated in fig. 5, which shows the plot Ap:” versus l/c”, where Api‘I1 is that part of stage III that remains at the peak temperature Ti”. The curves for both cases are clearly distinct. For comparison, fig. 6 shows the similar plot for molybdenum, with an additional curve for 2.5 MeV electron irradiation. It can be seen that in the molybdenum case the points for 10 MeV electrons and fission neutrons coincide on one curve, whereas the points for 2.5 MeV electrons lie on a
Table 1 Stage III activation energies for tungsten (eV) -~ Fission neutrons 10 MeV electrons ~_.__ 1.70 f 0.03
1.72 2 0.03
of structural defects in tungsten
different curve. We therefore are inclined to believe that the nature of the damage in tungsten folIowing IO MeV electrons is similar to that in molybdenum following 2.5 MeV efectrons. Calcuiation of the mean cascade volume yields indeed for both cases the same number of displaced atoms, namely 2 to 3 Frenkel pairs. Fig. 5 shows also that the points for reactor irradiation, fission neutron irradiation and cold-work lie on one single curve as also observed for molybdenum [6]. This indicates that the sink distributions in these cases are equally effective. The stage III activation energy measured for 10 MeV electrons and for fission neutrons is constant and within experimental error equal for both cases (see table 1). This points to a singly-activated recovery process for irradiated tungsten as it is also the case for moiybdenum 171. It is, furthermore, an indication for the fact that the different peak positions observed for equal defect concentrations is a matter of the number of jumps before annihilation. The same point defect is therefore migrating in both cases; only the sink distribution has been changed. It is, indeed, expected that the mean number of jumps of the migrating defect is larger in the 10 MeV electron case than in the fission neutron case, for the probability that the defect is annihilated within its own cascade volume is relatively large. This, of course, reduces the number of jumps with respect to the 10 MeV electron case. As far as the activation energy measurements for cold-worked tungsten are concerned, fig. 7 suggests a slight increase from 1.65 to 1.75 eV throughout stage III. A similar trend has also been observed for molybdenum [7]. Although in this case the main
Cold-work 1.65 t 0.03 to 1.75 * 0.03
1.3
0.2
0.4
0.6
Fig. 7. Stage III activation energy for cold worked tungsten.
J. Cornelis et al. /Recovery
of structural defects in tungsten
101
10
3. Concluding remarks
I i OE,
Without repeating the arguments developed in earlier papers on the high temperature recovery in molybdenum [6,7], we conclude that till now no experiments have been performed which unambiguously disprove interstitial migration in stage III of tungsten and molybdenum. There are, on the other hand, strong arguments against vacancy migration in stage III of iron, where positron annihilation data [lo] and hyperfine interaction measurements [ 151 point to vacancy migration above 400 K, whereas stage III is situated around 210 K [ 111. New experiments by Galligan and coworkers [ 121 point to the presence of single vacancies above stage III in highly pure tungsten. Finally it follows from the recent review by Doyama and Koehler [ 131 on vacancy formation energies that the most probable vacancy migration energies based on Eynv = Q,, - E,v.for molybdenum and tungsten are significantly higher than the activation energies associated with stage III. That review also strongly indicates that vacancy migration below room temperature in &Fe and Nb, as proposed by Schultz [ 141, has to be excluded.
0: 11
.m
600
__~_
0.6 L I t 031
LOO
800
600
T IK)
Fig. 8. Recovery of molybdenum and tungsten after 10 MeV electron irradiation.
recovery process is due to the migration of the same point species as in the two other cases, this increase in activation energy may be due to the migration of very small point defect clusters. In fig. 8 a comparison has been made between the recovery of tungsten and molybdenum following 10 MeV electron irradiation at equal Ap = 6 n&m. Stage IV is resolved for molybdenum and not for tungsten. From data of Moteff and coworkers [l] on neutron irradiated tungsten one can derive that independent of fluence the stage IV peak in tungsten occurs at a temperature about 200 K higher than the stage III peak. A similar effect has been observed for molybdenum, although the difference in peak temperature is there only =I00 K [6]. We are of the opinion that the present data for tungsten should show at least an increased recovery rate at about 900 K, which is evidently not the case. We are therefore inclined to believe that following 10 MeV electron irradiation stage IV is absent in tungsten and that this is due to the nature of the irradiation damage. Fig. 5 suggests indeed that this nature is similar to that in 2.5 MeV electron irradiated molybdenum, for which no stage IV has been observed either [8,9].
References [I] L.K. Keys, J.P. Smith and J. Moteff, Phys. Rev. 116 (1968) 851. [2] J. Moteff, Report GE-TM 65-9-2 (1965). [3] L.K. Keys and J. Moteff, Phys. Lett. 29 (1969) 106. [4] M.W. Thompson, Phil. Mag. 5 (1910) 218. [5] H. Schultz, in: Defects in Refractory metals, R. De Batist, J. Nihoul and L. Stab, eds. (Mol, 1912) p. 373. [6] J. Nihoul, L. Stals, J. Cornelis and P. De Meester, in: Defects and Defect Clusters in B.C.C. Metals and Their Alloys, R.J. Arsenault, ed.; Nucl. Met. 18 (1913) 108. [7] J. Cornelis, P. De Meester, L. Stals and J. Nihoul, Phys. Status Solidi (a) 18 (1973) 515. [8] M. De Jong and H.B. Afman, Acta Met. 15 (1961) 1. 191 H.B. Afman, Phys. Status Solidi Al3 (1972) 623. [lo] M. Weller, J. Diehl and W. Triftshluser, Solid State Commun. ll(1915) 1223. [ll] L.J. Cuddy, Acta Met. 16 (1968) 23. [ 121 J. Galligan, private communication. [ 131 M. Doyama and J.S. Koehler, Acta Met. 24 (1976) 811. [14] H. Schulz, Ser. Met. 8 (1974) 713. [ 151 F.R. Reitsema, Thesis, Univ. Groningen, The Netherlands (1976).
THE RECOVERY
704-707
OF STRUCTURAL
DEFECTS IN TUNGSTEN AFTER IRRADIATION
AND
AFTER COLD WORK
J. CORNELIS, L. STALS *, P. DE MEESTER +, J. ROGGEN ** and J. NIHOUL ” Materials Science Department,
SCK/CEN,
B-2400 MOL, Belgium
1. Introduction
tungsten, these peaks are surpassed by the important stage III recovery. If one compares the spectra after reactor neutron irradiation with those after fission neutron irradiation for equal amounts of stage III recovery, it turns out that the additional transmutation impurities do not influence stage III recovery nor do they influence the high temperature part of stage II recovery, although the total impurity level due to transmutation reactions has increased by about two orders of magnitude. The impurity level thus approaches values of about 20 ppm which is of the same order of magnitude as the total concentration of intrinsic defects annealing in stage II and stage III. It is interesting to compare the recovery spectra following fission neutron irradiation with those fol-
The present paper reports on a resistometric study of the isochronal and isothermal recovery of tungsten in the temperature range 300-900 K. Tungsten wires of 0.1 mm dia. were drawn from an electron beam refined single crystal with a resistivity ratio of >30 000 from Westinghouse Electric Corporation. The resistivity ratio of fully annealed wires lies between 1000 and 1600. These cold-worked wires were subjected to isochronal and isothermal annealing treatments between 300 and 900 K. Furthermore, the isochronal and isothermal recovery of annealed and subsequently irradiated specimens has been studied in the same temperature range. Various types of irradiations were applied: 10 MeV electrons, fast neutrons (fission spectrum of uranium) and reactor neutrons (BR2 spectrum).
__ 2. Experimental
2opy--
data and discussion
Figs. l-4 show.the recovery spectra of tungsten in the temperature range 300-900 K following coldwork (fig. l), reactor neutron irradiation (fig. 2) fission neutron irradiation (fig. 3) and 10 MeV electron irradiation (fig. 4). Stage III occurs between 600 and 850 K in agreement with earlier published data [l-5]. With the exception for cold-worked tungsten, the spectra show some small first order peaks belonging to stage II. In the case of cold-worked * Materials Physics Group, Limburgs Universitair Centrum, Diepenbeek, Belgium. ** IIKW bursar at Katholieke Universiteit Leuven, Laboratorium voor Vaste Stof Fysika en Magnetisme. + Departement Metaalkunde, Katholieke Universiteit Leuven ++ Also Katholieke Universiteit Leuven.
400
Fig. 1. Recovery
704
600
of tungsten
600
following
T(K)-cold-work.
J. Come& et al. /Recovery ofst~u~tu~a~defects in tungsten
_‘X
i
H $b
21
E
0
705
1A&(nQcm) 4.26
a* 4
l.!
Old,
400 600 800 TWFig. 2. Recovery of tungsten following reactor neutron irradiation. Fig. 4. Recovery of tungsten following 10 MeV electron irradiation.
--T(K) qlo
30
790
650
6
10-i
1.2
1.3
1.6
1.6 -$$3,-t,
0 400
600
800 (HI-
Fig. 3. Recovery of tungsten following fission neutron irradiation (fission spectrum of uranium).
-
,
Fig. 5. Plot of A#’ versus I/T:*I for tungsten. l 10 MeV electron irradiation; 0 fission neutron irradiation; . reactor irradiation; n cold-work.
106
J. Cornelis et al. /Recovery -TlKl
r
uo
8.
1.85
.I’.
500
SF0
. t d 1.90
195
2130 i$T'10-3K"~ 1
Fig. 6. Plot of A$’ versus l/T!” for molybdenum. q V 2-2.5 MeV electron irradiation [ 8,9] ; e 10 MeV electron irradiation; o fission neutron irradiation.
lowing 10 MeV electron irradiation. In both cases the total impurity level has in fact not changed by the irradiation. Less substructure in stage II following electron irradiation is observed. Furthermore, although the general appearance of stage III looks the same in both cases, there is, however, a remarkable difference in the recovery kinetics. This is clearly demonstrated in fig. 5, which shows the plot Ap:” versus l/c”, where Api‘I1 is that part of stage III that remains at the peak temperature Ti”. The curves for both cases are clearly distinct. For comparison, fig. 6 shows the similar plot for molybdenum, with an additional curve for 2.5 MeV electron irradiation. It can be seen that in the molybdenum case the points for 10 MeV electrons and fission neutrons coincide on one curve, whereas the points for 2.5 MeV electrons lie on a
Table 1 Stage III activation energies for tungsten (eV) -~ Fission neutrons 10 MeV electrons ~_.__ 1.70 f 0.03
1.72 2 0.03
of structural defects in tungsten
different curve. We therefore are inclined to believe that the nature of the damage in tungsten folIowing IO MeV electrons is similar to that in molybdenum following 2.5 MeV efectrons. Calcuiation of the mean cascade volume yields indeed for both cases the same number of displaced atoms, namely 2 to 3 Frenkel pairs. Fig. 5 shows also that the points for reactor irradiation, fission neutron irradiation and cold-work lie on one single curve as also observed for molybdenum [6]. This indicates that the sink distributions in these cases are equally effective. The stage III activation energy measured for 10 MeV electrons and for fission neutrons is constant and within experimental error equal for both cases (see table 1). This points to a singly-activated recovery process for irradiated tungsten as it is also the case for moiybdenum 171. It is, furthermore, an indication for the fact that the different peak positions observed for equal defect concentrations is a matter of the number of jumps before annihilation. The same point defect is therefore migrating in both cases; only the sink distribution has been changed. It is, indeed, expected that the mean number of jumps of the migrating defect is larger in the 10 MeV electron case than in the fission neutron case, for the probability that the defect is annihilated within its own cascade volume is relatively large. This, of course, reduces the number of jumps with respect to the 10 MeV electron case. As far as the activation energy measurements for cold-worked tungsten are concerned, fig. 7 suggests a slight increase from 1.65 to 1.75 eV throughout stage III. A similar trend has also been observed for molybdenum [7]. Although in this case the main
Cold-work 1.65 t 0.03 to 1.75 * 0.03
1.3
0.2
0.4
0.6
Fig. 7. Stage III activation energy for cold worked tungsten.
J. Cornelis et al. /Recovery
of structural defects in tungsten
101
10
3. Concluding remarks
I i OE,
Without repeating the arguments developed in earlier papers on the high temperature recovery in molybdenum [6,7], we conclude that till now no experiments have been performed which unambiguously disprove interstitial migration in stage III of tungsten and molybdenum. There are, on the other hand, strong arguments against vacancy migration in stage III of iron, where positron annihilation data [lo] and hyperfine interaction measurements [ 151 point to vacancy migration above 400 K, whereas stage III is situated around 210 K [ 111. New experiments by Galligan and coworkers [ 121 point to the presence of single vacancies above stage III in highly pure tungsten. Finally it follows from the recent review by Doyama and Koehler [ 131 on vacancy formation energies that the most probable vacancy migration energies based on Eynv = Q,, - E,v.for molybdenum and tungsten are significantly higher than the activation energies associated with stage III. That review also strongly indicates that vacancy migration below room temperature in &Fe and Nb, as proposed by Schultz [ 141, has to be excluded.
0: 11
.m
600
__~_
0.6 L I t 031
LOO
800
600
T IK)
Fig. 8. Recovery of molybdenum and tungsten after 10 MeV electron irradiation.
recovery process is due to the migration of the same point species as in the two other cases, this increase in activation energy may be due to the migration of very small point defect clusters. In fig. 8 a comparison has been made between the recovery of tungsten and molybdenum following 10 MeV electron irradiation at equal Ap = 6 n&m. Stage IV is resolved for molybdenum and not for tungsten. From data of Moteff and coworkers [l] on neutron irradiated tungsten one can derive that independent of fluence the stage IV peak in tungsten occurs at a temperature about 200 K higher than the stage III peak. A similar effect has been observed for molybdenum, although the difference in peak temperature is there only =I00 K [6]. We are of the opinion that the present data for tungsten should show at least an increased recovery rate at about 900 K, which is evidently not the case. We are therefore inclined to believe that following 10 MeV electron irradiation stage IV is absent in tungsten and that this is due to the nature of the irradiation damage. Fig. 5 suggests indeed that this nature is similar to that in 2.5 MeV electron irradiated molybdenum, for which no stage IV has been observed either [8,9].
References [I] L.K. Keys, J.P. Smith and J. Moteff, Phys. Rev. 116 (1968) 851. [2] J. Moteff, Report GE-TM 65-9-2 (1965). [3] L.K. Keys and J. Moteff, Phys. Lett. 29 (1969) 106. [4] M.W. Thompson, Phil. Mag. 5 (1910) 218. [5] H. Schultz, in: Defects in Refractory metals, R. De Batist, J. Nihoul and L. Stab, eds. (Mol, 1912) p. 373. [6] J. Nihoul, L. Stals, J. Cornelis and P. De Meester, in: Defects and Defect Clusters in B.C.C. Metals and Their Alloys, R.J. Arsenault, ed.; Nucl. Met. 18 (1913) 108. [7] J. Cornelis, P. De Meester, L. Stals and J. Nihoul, Phys. Status Solidi (a) 18 (1973) 515. [8] M. De Jong and H.B. Afman, Acta Met. 15 (1961) 1. 191 H.B. Afman, Phys. Status Solidi Al3 (1972) 623. [lo] M. Weller, J. Diehl and W. Triftshluser, Solid State Commun. ll(1915) 1223. [ll] L.J. Cuddy, Acta Met. 16 (1968) 23. [ 121 J. Galligan, private communication. [ 131 M. Doyama and J.S. Koehler, Acta Met. 24 (1976) 811. [14] H. Schulz, Ser. Met. 8 (1974) 713. [ 151 F.R. Reitsema, Thesis, Univ. Groningen, The Netherlands (1976).