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Vacancy reactions in stage III recovery of molybdenum
Scripta
METALLURGICA
V o l . 13, pp. 3 2 7 - 3 2 8 , Printed in the U . S . A .
VACANCY REACTIONS
1979
Pergamon P r e s s Ltd. All rights reserved.
IN STAGE III RECOVERY OF MOLYBDENLrM
H. E. KISSINGER AND J. L. BRIMHALL Battelle Memorial Institute, Pacific Northwest Laboratory Richland, Washington 99352 (Received December ( R e v i s e d M a r c h 29,
ii, 1978) 1979)
The controversy in regard to the one-interstitial model vs. the two interstitial model for recovery of radiation damage in metals has flared vigorously for twenty years but is apparently subsiding with the bulk of experimental evidence supporting the one-interstitial model. The controversial points are well summarized in reviews by Schilling, Ehrhart and Sonneberg (i) and by Seeger (2). Evidence in favor of a particular model is relatively easy to obtain, since most recovery phenomena can be explained by variations of either model. Evidence a~ainst a particular model is therefore limited and very seldom irrefutable. In this note some experimental observations are presented which bear directly on one of the crucial points of the one-interstitial--two interstitial debate, specifically the role of self-interstitial defects in Stage III recovery in molybdenum. Single-crystal rods of high-purity Mo, 3 mm diameter, were prepared by multiple-pass zone refining. One rod having a {144} orientation was cut into 40 mm lengths and each section provided with a (01~) face parallel to the rod axis. Lengths were measured by a gageblock comparator method to 0.001%, while the Bond method (3) was used to measure lattice parameters with equivalent precision. Details of the sample preparation and characterization have been reported previously (4). These crystal rods were irradiated at 40°C to several fluence levels in a Hanford reactor (5). Postirradiation study consisted of 2-hour isochronal anneals with length, lattice parameter, and hardness measurements after each anneal. A separate sample was used for the hardness measurements to avoid any possibility of interference. Results of these measurements are shown in Fig. i for a sample irradiated to 4xl019 n/cm 2 (E>I MeV).
.04
~.o2
~o ~5o L
I
i
~ am
,
J ~
,
J mm
AN~IEALINGTEMPERATURE.C~c
Figure I Lattice parameter, length change, and microhardness recovery for neutronirradiated molybdenum single crystals.
The combined measurements show clearly that resistance and hardness recovery proceed normally while no length or lattice parameter change may be observed under 200°C. The resistance decrease indicates fewer scattering centers, apparently as a result of agglomeration of defects with no change in effective volume per defect (6). Positron annihilation experiments (7) indicate vacancy cluster growth at these temperatures. The larger complexes are stronger barriers to dislocation motion, as indicated by the anneal hardening observed below 200°C. The 3 mm by 40 mm rods were unsuited for resistance recovery studies. Therefore, a third crystal of this sample suite was cut lengthwise into 0.5 mm by 0.5 mm sections. Similar sections from an unirradiated crystal provided reference specimens to assess the effect of the sectioning (with a watercooled diamond saw) on the resistance recovery. Less than i% of the observed recovery could be ascribed 327
328
RECOVERY OF M O L Y B D E N U M
Vol.
13, No.
5
to the sectioning technique. Resistance recovery of the irradiated sample was measured ~sothermally at 134 ° , 162 ° , and 167°C, and an activation energy of 1.20 ± 0.i ev was calculated for the resistance annealing. This indicates that the recovery observed was characteristic of the Stage III which occurs in this temperature range. The experimental points are shown in Figure 2.
w1 . O ~ ~
.----_____.__ ~
._
163%
FICURF 2
~ 0.9
0.8
Isothermal resistance recovery for the neutronirradiated molybdenum crystal.
I 30
I 60
I 90
I 120
TIME - MINUTES
Above 200°C the crystal volume begins to decrease and a slight lattice parameter increase is noted. These could be manifestations of a collapse of vacancy clusters to loops with the lattice parameter change reflecting the recovery of elastic relaxations about the vacant sites. A change in anneal-hardening characteristics also is observed at 200°C in agreement with the change in dislocation barrier structure. Since self-interstitial point defects have a substantial effect on lattice parameter (8), there was at most a very slight change in interstitial concentration during the entire Stage III recovery. The two-interstitial model ascribes all of Stage III to an interstitial defect which migrates and annihilates at this temperature. As no such migration and annihilation was observed, the two-interstitial model is untenable in the present case. Acknowledgement This work was supported by the United States Department of Energy under Contract EY-76-C-06-1830. i.
2.
3. 4. 5.
6.
7. 8.
References W. Schilling, P. Ehrhart, and K. Sonnenbergin Fundamental Aspects of Radiation Damage in Metals, Proceedings of a Conference at Gatlinburg, Tennessee October 1975, M.T. Robinson and F. W. Young Jr., Eds. U.S. Energy Research and Development Administration Report CONF-741006-PI, Oak Ridge, Tenn. 1975, p. 470. A. Seeger, in Fundamental Aspects of Radiation Damage in Metals, Proceedings of a conference at Gatlinburg, Tennessee October 1975, M. T. Roglnson and F. W. Young, Jr., Eds. U.S. Energy Research and Development Administration Report CONF-741006-PI, Oak Ridge, Tenn. 1975, p.493. W. L. Bond, Acta Cryst. 13, 814 (1960). H. E. Kisslnger, J. L. Brimhall, B. Mastel, Materials Research Bulletin 2, 437, (1967). H. E. Kissinger, J. L. Brimhall, B. Mastel, and T. K. Bierleln, in International Conference on Vacancies and Interstitials in Metals, preprlnts of conference papers, Kernforschungsanlage Julich, Germany 1968, p. 681. E. P. Simonen, H. E. Kissinger, J. L. Brimhall, in Properties of Atomic Defects in Metals, N. L. Peterson and R. W. Siegel, Eds. North-Holland Publishing Compnay, Amsterdam (1978) pp. 724-726 K. Peterson, N. Thomas, R. M. J. Cotterill, Phil. Mag. 2_~9, 9, (1974) P. Ehrhart, in Properties of Atomic Defects in Metals, N. L. Peterson and R. W. Siege, Eds., North-Holland Publishing Company, Amsterdam 1978, pp. 200-214.
METALLURGICA
V o l . 13, pp. 3 2 7 - 3 2 8 , Printed in the U . S . A .
VACANCY REACTIONS
1979
Pergamon P r e s s Ltd. All rights reserved.
IN STAGE III RECOVERY OF MOLYBDENLrM
H. E. KISSINGER AND J. L. BRIMHALL Battelle Memorial Institute, Pacific Northwest Laboratory Richland, Washington 99352 (Received December ( R e v i s e d M a r c h 29,
ii, 1978) 1979)
The controversy in regard to the one-interstitial model vs. the two interstitial model for recovery of radiation damage in metals has flared vigorously for twenty years but is apparently subsiding with the bulk of experimental evidence supporting the one-interstitial model. The controversial points are well summarized in reviews by Schilling, Ehrhart and Sonneberg (i) and by Seeger (2). Evidence in favor of a particular model is relatively easy to obtain, since most recovery phenomena can be explained by variations of either model. Evidence a~ainst a particular model is therefore limited and very seldom irrefutable. In this note some experimental observations are presented which bear directly on one of the crucial points of the one-interstitial--two interstitial debate, specifically the role of self-interstitial defects in Stage III recovery in molybdenum. Single-crystal rods of high-purity Mo, 3 mm diameter, were prepared by multiple-pass zone refining. One rod having a {144} orientation was cut into 40 mm lengths and each section provided with a (01~) face parallel to the rod axis. Lengths were measured by a gageblock comparator method to 0.001%, while the Bond method (3) was used to measure lattice parameters with equivalent precision. Details of the sample preparation and characterization have been reported previously (4). These crystal rods were irradiated at 40°C to several fluence levels in a Hanford reactor (5). Postirradiation study consisted of 2-hour isochronal anneals with length, lattice parameter, and hardness measurements after each anneal. A separate sample was used for the hardness measurements to avoid any possibility of interference. Results of these measurements are shown in Fig. i for a sample irradiated to 4xl019 n/cm 2 (E>I MeV).
.04
~.o2
~o ~5o L
I
i
~ am
,
J ~
,
J mm
AN~IEALINGTEMPERATURE.C~c
Figure I Lattice parameter, length change, and microhardness recovery for neutronirradiated molybdenum single crystals.
The combined measurements show clearly that resistance and hardness recovery proceed normally while no length or lattice parameter change may be observed under 200°C. The resistance decrease indicates fewer scattering centers, apparently as a result of agglomeration of defects with no change in effective volume per defect (6). Positron annihilation experiments (7) indicate vacancy cluster growth at these temperatures. The larger complexes are stronger barriers to dislocation motion, as indicated by the anneal hardening observed below 200°C. The 3 mm by 40 mm rods were unsuited for resistance recovery studies. Therefore, a third crystal of this sample suite was cut lengthwise into 0.5 mm by 0.5 mm sections. Similar sections from an unirradiated crystal provided reference specimens to assess the effect of the sectioning (with a watercooled diamond saw) on the resistance recovery. Less than i% of the observed recovery could be ascribed 327
328
RECOVERY OF M O L Y B D E N U M
Vol.
13, No.
5
to the sectioning technique. Resistance recovery of the irradiated sample was measured ~sothermally at 134 ° , 162 ° , and 167°C, and an activation energy of 1.20 ± 0.i ev was calculated for the resistance annealing. This indicates that the recovery observed was characteristic of the Stage III which occurs in this temperature range. The experimental points are shown in Figure 2.
w1 . O ~ ~
.----_____.__ ~
._
163%
FICURF 2
~ 0.9
0.8
Isothermal resistance recovery for the neutronirradiated molybdenum crystal.
I 30
I 60
I 90
I 120
TIME - MINUTES
Above 200°C the crystal volume begins to decrease and a slight lattice parameter increase is noted. These could be manifestations of a collapse of vacancy clusters to loops with the lattice parameter change reflecting the recovery of elastic relaxations about the vacant sites. A change in anneal-hardening characteristics also is observed at 200°C in agreement with the change in dislocation barrier structure. Since self-interstitial point defects have a substantial effect on lattice parameter (8), there was at most a very slight change in interstitial concentration during the entire Stage III recovery. The two-interstitial model ascribes all of Stage III to an interstitial defect which migrates and annihilates at this temperature. As no such migration and annihilation was observed, the two-interstitial model is untenable in the present case. Acknowledgement This work was supported by the United States Department of Energy under Contract EY-76-C-06-1830. i.
2.
3. 4. 5.
6.
7. 8.
References W. Schilling, P. Ehrhart, and K. Sonnenbergin Fundamental Aspects of Radiation Damage in Metals, Proceedings of a Conference at Gatlinburg, Tennessee October 1975, M.T. Robinson and F. W. Young Jr., Eds. U.S. Energy Research and Development Administration Report CONF-741006-PI, Oak Ridge, Tenn. 1975, p. 470. A. Seeger, in Fundamental Aspects of Radiation Damage in Metals, Proceedings of a conference at Gatlinburg, Tennessee October 1975, M. T. Roglnson and F. W. Young, Jr., Eds. U.S. Energy Research and Development Administration Report CONF-741006-PI, Oak Ridge, Tenn. 1975, p.493. W. L. Bond, Acta Cryst. 13, 814 (1960). H. E. Kisslnger, J. L. Brimhall, B. Mastel, Materials Research Bulletin 2, 437, (1967). H. E. Kissinger, J. L. Brimhall, B. Mastel, and T. K. Bierleln, in International Conference on Vacancies and Interstitials in Metals, preprlnts of conference papers, Kernforschungsanlage Julich, Germany 1968, p. 681. E. P. Simonen, H. E. Kissinger, J. L. Brimhall, in Properties of Atomic Defects in Metals, N. L. Peterson and R. W. Siegel, Eds. North-Holland Publishing Compnay, Amsterdam (1978) pp. 724-726 K. Peterson, N. Thomas, R. M. J. Cotterill, Phil. Mag. 2_~9, 9, (1974) P. Ehrhart, in Properties of Atomic Defects in Metals, N. L. Peterson and R. W. Siege, Eds., North-Holland Publishing Company, Amsterdam 1978, pp. 200-214.