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Nickel-ion bombardment of annealed and cold-worked type 316 stainless steel
JOURNAL OF NUCLEAR MATERIALS 48 (1973) 330-338.0
NORTH-HOLLAND PUBLISHING COMPANY
NICKEL-ION BOMBARDMENT OF ANNEALED AND COLD-WORKED TYPE 316 STAINLESS STEEL W.G. JOHNSTON, J.H. ROSOLOWSKI and A.M. TURKALO General Electric, Corporate R&D, Schenectady,
New York 12301,
USA
and T. LAURITZEN General Electric Breeder Reactor Department,
Sunnyvale, California 94086,
USA
Received 17 May 1973 Revised manuscript received 2 July 197 3 Bombardment with high doses of 5 MeV nickel ions has produced swellings as high as 90% and 60%, respectively, in annealed and 20% cold-rolled Type 316 steels. The steels contained 15 ppm of cyclotron-injected helium. Swellings were determined by both transmission electron microscopy and by a step-height method that measures the total swelling integrated along the ion path. The swelling in annealed Type 316 has a pronounced peak in the vicinity of 625°C which is about 155°C higher than the peak swelling temperature in-reactor. The magnitudes of the swelling, void densities and void sizes produced in annealed Type 316 by nickel ions and in-reactor at the respective peak swelling temperatures are similar and it is concluded that the nickel ion bombardments provide an acceptable simulation of in-reactor behavior. Using the high dose ion results to guide extrapolation of presently available EBR-II data to higher fluences leads to the prediction that the swelling of annealed Type 316 steel at the peak swelling temperature will reach 40% at 2 X 10z3 n/cm’ (E > 0.1 MeV) in EBR-II core, and 70% at 3 X 10z3 n/cm2. These fluencesin EBR-II correspond to 155 and 230 dpa respectively. Twenty percent reduction by cold-rolling reduces the ion produced swelling by 35% at 625°C and by 50% at 575°C. Le bombardement avec des ions nickel de 5 MeV a fortes doses a produit des gonflements de 90% et 60% dans les aciers type 316 respectivement recuits et ecrouisde 20%. Les aciers contenaient 15 ppm d’hklium inject; au cyclotron. Les gonflements dtaient determines a la fois par microscopic ilectronique en transmission et par une mdthode de hauteur de pas qui permet de mesurer le gonflement total intdgre le long du trajet de l’ion. Le gonflement dans le type 316 recuit presente un pit prononce aux environs de 625”C, qui est d’environ 115°C superieur i la temperature correspondant au pit de gonflement en reacteur. Les amplitudes du gonflement, les densites des vides et les dimensions des vides produits dans le type 316 recuit, soit par les ions nickel, soit en reacteur aux temperatures respectives correspondant au pit de gonflement, sont similaires et iJ est conclu que le bombardement par les ions nickel constitue une simulation acceptable du comportement en rdacteur. L’utihsation des risultats obtenus a l’aide des ions a forte dose pour guider l’extrapolation des donnees disponibles actuellement pour EBR-II ‘ades flux plus eleves:perme\ de prdvoir que le gonflement dans l’acier type 316 recuit. a la tempe’rature du pit de gonflement, atteindra 40% H 2 X 10’ n/cm (E > 0,l MeV) dans le coeur de EBR-II et 70% a 3X 1023n/cm2. Ces fluences correspondent dans le riacteur EBR-II 2 155 et 230 dpa respectivement. 20% de reduction par laminage 3 froid reduisent le gonflement produit par les ions de 35% 5 625°C et de 50% B 575°C. Die Bestrahlung mit einer hohen Dosis 5 MeV Ni-lonen verursacht in warmebehandeltem und 20% kaltverformtem Stahl 316 ein Schwellen von 90 bzw. 60%. Der Stahl enthalt 15 ppm He, das mit einem Zyklotron implantiert wurde. Das Schwellen wurde transmissionselektronenmikroskopisch und nach einer Stufenhohen-Methode bestimmt, nach der der gesarnte, iiber die Spur der lonen integrierte Schwellbetrag gemessen wird. Das Schwellen in wlrmebehandeltem Stahl 316 hat ein ausgeprsgtes Maximum urn 625”C, das etwa 115°C hoher als die Temperatur des Schwellmaximums im Reaktor ist. Der Schwellbetrag, die Porendichte und die Porengrosse, die durch Bestrahlung mit Ni-lonen im Stahl 316 entstehen, sind den Grossen im Reaktor bei der entsprechenden Temperatur des Schwellmaximums Zhnlich. Daraus wird geschlossen, dass die Bestrahlung mit Ni-lonen das Verhahen im Reaktor angemessen simuliert. Die Ergebnisse ermaglichen eine Extrapolation der genenwertig vorliegenden EBR-II-Daten zu h8heren Dosen und die Voraussage, dass das Schwellen von wlrmebehandeltem Stahl 316 im EBR-II-Reaktor bei der Temperatur des maximalen Schwellens 40% bei 2X 1O23 n/cm2 (E > 0,l MeV) und 70% bei 3 X 1O23n/cm2 erreicht. Diesen Dosen entsprechen
W.G.Johnston et al., Annealed and cold-worked type 316 stainlesssteel
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155 und 230 Verlagerungen pro Atom. Eine 2O%ige Reduktion durch Kaltwalzen erniedrigt das durch Ionenbeschuss verursachte Schwellen bei 625°C urn 35% und bei 575°C urn 50%.
1. Introduction The void swelling behavior of Type 3 16 stainless steel is of particular interest because this alloy has been designated for use as fuel cladding in the British prototype liquid metal fast breeder reactor, (PFR) and in the United States demonstration plant. Both reactors will use cold-worked Type 3 16. At present, there do not exist swelling data at the ultimate fast fluences that are expected in these reactors; but Harwell workers, Mazey, Hudson and Nelson [ 11,have subjected Type 316 steel to carbon ion bombardment up to doses of 400 displacements per atom (dpa). Two results of the Harwell work are that the swelling in solution-annealed Type 316 saturates at less than 15% swelling at 525°C [l] and that cold-worked Type 316 swells somewhat less than the annealed Type 3 16 [2,3]. The work of Taylor and McDonald [4] and of Keefer, Pard and Kramer [5], as well as our own recent work with 5 MeV nickel ion bombardment of Type 304 steel [6] demonstrated conclusively that saturation of swelling at a low value is not a generalcharacteristic of austenitic stainless steel bombarded with energetic particles. We have produced swellings of well over 50% at the peak swelling temperature without indication of saturation. The nickel ion bombardment seemed to provide a good simulation of presently available reactor data on solution-annealed Type 304, and using the high dose ion data to guide extrapolation of the reactor data to higher fluences led to the prediction of about 50% swelling at the peak swelling temperature in EBR-II (about 475°C) at a fluence of 2 X 1023 n/cm2 (E > 0.1 MeV). In the present work, the experimental techniques that were developed and tested on the Type 304 have been applied to Type 316 steel to further investigate the high dose behavior of this material and to learn how prior cold-work affects the swelling at high damage levels under ion bombardment. Two techniques were used for measuring swelling of Type 304; one was conventional transmission electron microscopy (TEM), and the other was a stepheight measurement of the gross swelling [7]. The latter method involves covering the specimen with a partial mask during ion bombardment so that some
regions are bombarded while others are protected. As the bombarded regions swell, the surface becomes elevated and a step forms at the boundary of the masked regions. The height of the step can be measured with a stylus-type profilometer or by interferometry and gives the total swelling integrated along the range of the bombarding particles. The step-height technique is inherently a simple and reliable measurement that can be extended to higher swellings than conventional TEM can measure. At swellings of the Type 304 steel where the two techniques overlapped, the step-height method and TEM measurements were in good agreement. The experimental techniques, including calculation of the damage curve, helium injection, specimen preparation, nickel ion bombardment, examination by TEM, and measurement of step-heights have been described in detail [6] and will not be further discussed in this paper. The approach to the investigation of the solutionannealed Type 316 has been the same as that which we pursued with the Type 304 steel. The temperature dependence of void swelling was determined, and the dose dependence of the swelling at the peak swelling temperature was measured. The results of ion bombardments will be compared with data on in-reactor behavior, and we shall use the high dose ion data to guide extrapolation of the reactor data to the higher fluences that are of interest. The swelling behavior of 20% cold-worked Type 3 16 will be compared with that of the solution-annealed steel from the same heat. At the outset, we recognize a complication in doing heavy ion bombardments of the cold-worked steel. By necessity, the heavy ion damage, which results from very high displacement rates, must be carried out at a higher temperature than the corresponding in-reactor bombardments. This presents the possibility that the higher temperatures in the ion bombardment experiments may anneal some of the cold work. The possibility of annealing seems particularly strong in view of the recent work of Straalsund and Brager [8] who showed that the beneficial effect of cold-work in reducing in-reactor swelling of Type 3 16 was lost in 100 h at 650°C.
W.G. Johnston
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et al., Annealed and cold-worked
2. TEM measurements of swelling of annealed Type 316 steel The commercial Type 3 16 steel, with the composition given in table 1, was annealed in vacuum at 1010 “C for one hour and rapidly cooled in argon. Specimens about 125 pm thick and 3 mm in diameter, containing 15 atomic ppm of helium, injected uniformly with a cyclotron, were electropolished and bombarded with 5 MeV nickel ions [6]. The flux of nickel ions was - 1.3 X 1013 ions/cm*. set which corresponds to a displacement rate of approx&ately 2 X lOA dpa/ set at the peak damage region where foils were taken for TEM analysis. The method for determining the position of the TEM foils along the range of the bombarding ions has been described [6]. The void densities and sizes were determined from stereoscopic pairs of electron micrographs taken at 100 kV. The swelling is reported as A V/V, = A V/( V - A V), where A V is the void volume in a foil of volume, V.
I
7
I
1
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I
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I
TYPE 316 ANNEALED
/
1
1
,/---\
/’ ’ -REAcTwt 6.7
type 316 stainless steel
Table 1 Analysis of Type 3 16 steel in weight percent Cr Ni MO Mn Si cu co
C N P s B Nb Ti Fe
17.03 13.18 2.10 1.83 0.72 0.14 0.13
0.055
0.036 0.017 0.008 0.0015 < 0.02 < 0.02 balance
The temperature dependence of void swelling as measured by TEM is shown in fig. 1. There is a maximum in the swelling at about 625°C. The temperature dependence of swelling in the core of EBR-II as given by the empirical expression of Bates and Straalsund [9] is shown by the curve on the left in fig. 1. The peak swelling temperature for the ion bombardment is about 115°C higher than the peak swelling temperature in-reactor. In order to investigate the greatest swelling that will occur in Type 3 16 steel, the dose dependence of ion-produced swelling was measured at the peak swelling temperature, 625’C, and the results are shown in fig. 2. At the highest damage level of about 230 dpa, the swelling was about 50%. Also shown in fig. 2 is
‘\
x lo**“/cM* (FAST)
TYPE 316 625’C 15
ppm He PJ
i
ION BDMBARDYENT
D.lL 400
,
I 500
600
,
,
-
700
TEMPERATURE, ‘C
Fig. 1. Temperature dependence of swelling in annealed Type 316 stainless steel bombarded with 5 MeV nickel to a damage level of 67 dpa. The steel contained 15 ppm of cyclotron-injected helium. The temperature dependence of EBR-II Core swelling [7] is shown by the dashed curve.
D.ll ’ “I” 4
I 100
IO DISPLACENEWTS
L I,II IDOD
PER ATOY
Fig. 2. Dose dependence of ion-produced swelling in annealed Type 316 steel at the peak swelling temperature of 625’C.
W.G.Johnston et al., Annealed and cold-worked type 316
stainlesssteel
333
625.C *Ii.
625% r/oHa I
100
lo’3L
DISPLACEMENTSPER ATON
Fig. 3. Average void diameters in ion-bombarded annealed Type 316. the dose dependence of swelling for helium-free steel at 625°C. It should be noted that we have previously pointed out the limitations of TEM at 100 kV in measuring large swellings and large void sizes [6]. The void sizes and densities measured in order to determine the swellings of annealed Type 316 are shown in figs. 3 and 4. The void sizes increase monotonically with dose, while the void densities increase at low doses and pass through a maximum. The maximum in the void density seems to correlate with the amount of swelling rather than with the damage level. We have observed in several alloys that the void density maximum occurs at 6 to 10% swelling. The arrows in fig. 4 indicate the doses at which 6% swelling is achieved in the three caSes shown. At 6% swelling the average spacing of voids is twice the void diameter, assuming a uniform void size in order to simplify the calculation. The swelling is appreciably less in helium-free Type 3 16 than in the helium-injected steel bombarded at the same temperature, and the difference is due to the much lower void densities in the absence of helium. This large effect of helium on void nucleation,‘which was also seen in Type 304 steel [6], was first reported by Nelson and Mazey [ lo]. 3. Step-height measurements of swelling in annealed Type 316 Helium-injected
specimens of annealed Type 3 16
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I
1111’
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,
1000
100
DISPLACEMENTSPER ATOM
Fig. 4. Void densities in ion-bombarded annealed Type 316. steel were partially masked and bombarded with 5 MeV nickel ions at 625°C. The step height at the boundary of the unirradiated region and the elevated, irradiated region was measured with a stylus-type profilometer [7]. The results are presented in table 2 for several ion doses. Each reported step-height is the average of eight measurements at different locations on one specimen. The measurements have been corrected for the amount of nickel injected during born-: bardment. The step height due to surface elevation is a measure of the total integrated swelling along the range of the bombarding ions. From the step-heights at several ion doses and the damage curve for nickel
Table 2 Step-heights on annealed Type 316. Step-height calculated
Ion dose
Measured step-height
(lO”/cm’)
(A)
from swelling curvea)
0.5 1.0 2.0
290 f 50 1700 f 1.50 5500 f 400
298 1660 5530
akhe swelling curve was inferred from the step-height data. The calculated step-heights merely indicate how well the curve has been constructed.
W.G. Johnston
et al., Annealed and cold-worked type 316 stainless steel
0 x
-
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STEPHEWtlT DATA
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F&S. Swelling curve for annealed Type 316 inferred from step-height measurements. TEM data points are shown for comparison.
Fig. 6. Comparison of EBR-II [7] and nickel ion-produced swellings in annealed Type 3 16 at the respective peak swelling temperatures.
ions in stainless steel, it is possible to deduce the swelling versus dpa curve shown in fig. 5 [6]. As a check, the swelling curve can be used to predict the step-height values, and the agreement between the calculated and observed step-height in table 2 is an indication of how well the curve has been constructed. Also plotted in fig. 5 are the data points for swelling versus dpa as determined by TEM. Comparison of the curve and the TEM data points indicates that the swelling as determined by step-height measurements is slightly larger than that determined by TEM. The step-height measurement [7] is inherently a more simple, direct and reliable measurement of total swelling than is the TEM measurement, so we tend to place more credence in the result of step-height measurements.
a theoretical calculation of how the temperature should scale with atom displacement rate. However, in the absence of firm experimental verification of such calculations, we prefer to follow the empirical approach we took in the work on Type 304 [6]. As shown in fig. 1, the peak swelling temperature for the ion bombardments was about 115°C higher than for in-reactor swelling. In order to compare the maximum swellings for the two types of data, we shall compare the swellings at the peak swelling temperatures. The ion data at 625°C will be compared with EBR-II swelling data in the temperature range of 5 10°C + 30°C. We select the reactor data in a temperature range because there do not exist sufficient data at one single temperature. In comparing the damage produced by fast neutrons with that due to heavy ions, we shall use the conversion of 1O23 n/cm* (E > 0.1 MeV) equivalent to 77.4 dpa. This conversion is taken from the calculations of Doran [ 12,131 for EBR-II core, as discussed in ref. [6]. A comparison of in-reactor swelling with ion bombardment results determined by TEM and by stepheight measurements is presented in fig. 6. The reactor data are from the compilation of Bates and Straalsund [9] which includes data of a number of investi-
4. Comparison of ion bombardment results with inreactor swelling of annealed Type 316 steel In order to compare in-reactor swelling with swelling produced by heavy ions it is necessary to properly scale the temperatures in the two cases, and to relate the damage levels produced by ions to those produced by fast neutrons. Bullough and Perrin [ 1 l] have made
W.G. Johnston
et al., Annealed and cold-worked
FLUENCE, n/cm*
FLUENCE, n/cm* 102’
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335
type 316 stainless steel
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Fig. 7. Comparison of void sizes produced in annealed Type 316 in EBR-II [ 141 and by ion-bombardment at the respective peak swelling temperatures.
Fig. 8. Comparison of void densities produced in annealed Type 316 in EBR-II [ 141 and by ion-bombardment at the respective peak swelling temperatures.
gators. The solid curve was obtained from our stepheight measurements and the X’s are TEM data points, both on nickel ion bombarded specimens. The stepheight curve is closer to the reactor data than are the TEM points, but both show swellings that are on the low side of the reactor results. The slope of the reactor and ion data are similar in the fluence range where they overlap, and as the ion data continue to high damage levels and swellings, they should provide a conservative prediction of in-reactor swelling at higher fluences. The similarity of the swelling produced by ions and in-reactor at comparable damage levels is further borne out in the comparison of void sizes and densities [ 141 for the two cases, presented in figs. 7 and 8. Although the magnitudes of the ion and neutron produced swellings compared in the above manner do not agree as well as they did for annealed Type 304 [6], the agreement is sufficiently good, particularly in view of the similarity of void sizes and densities, to conclude that the ion bombardment provides an acceptable simulation of the reactor damage, and that thehigh dose ion data can be used to guide extrapolation of reactor data to higher fluences. An extrapolation of in-reactor data based on our high dose nickel ion results indicates that the swelling in annealed Type 3 16 at the peak swelling temperature in EBR-II core should reach about 40% at a fluence of 2 X 1023 n/cm2 (E > 0.1 MeV) and about 70%
at 3 X 1O23n/cm2. (These fluences correspond to 155 and 230 dpa respectively.) We judge these to be conservative extrapolations of the reactor data, since the ion-produced swellings lie lower than the reactor data in fig. 6. 5. Swelling of 20% cold-worked Type 3 16 Solution-annealed Type 3 16 steel from the heat described in table 1 was cold-rolled 20 + 2% from a foil thickness of 125 pm. The 20% reduction of the thin foil could not be accomplished in a single rolling pass, but required several passes. Therefore, the coldworked structure may differ from that produced by a single 20% deformation, (such as in cold-drawn seamless cladding tubes). Following the cold-work, helium was injected uniformly into the foil to produce a concentration of 15 atomic ppm. Nickel ion bombardments were carried out at 575°C and 625°C and the TEM measurements of swelling are shown in fig. 9. Prior to the ion bombardments, the specimens were heated to 25°C above the subsequent bombardment temperature for a period of between 15 and 30 min as part of an outgassing procedure. The most extreme annealing in the present work would have occurred in one-half hour at 65O’C followed by 4: h at 625°C during the actual bombardment. For the lower temperature runs, the most extreme (annealing was 1 h at 600°C followed by 41 h at 575°C.
336
W.G. Johnston
et al., Annealed and cold-worked type 316 stainless steel
U6PLACEmTS PER ATOM (626-C) d’00j
STEP HENIT
I. IO
DATA
100
500
DISPLACEMENTSPER ATOM DISPLACEMENTSPER ATOM (575'Cl
Fig. 9. Swelling determined by TEM in annealed Type 316 and 20% cold-rolled Type 316, bombarded with 5 MeV nickel ions Note that the upper abscissa scale refers to the 625°C data and the lower scale refers to the 575°C data.
The TEM data in fig. 9 show appreciable scatter for swelling at 575°C; nevertheless, it appears that the cold-work has resulted in a reduction of about 50% in the swelling. At 625’C, the solution annealed and cold-worked data appear similar; the scatter is sufficient to mask a relatively small effect of the coldwork, such as that reported from step-height measurements in the following paragraph. Step-height measurements of the swelling produced in cold-worked Type 3 16 at 625°C gave the results listed in table 3; and the swelling versus dpa curve constructed from the data is shown in fig. 10, along with Table 3 Step-heights on cold-worked Type 316.
Ion dose (101’/cm2)
Measured step-height (A)
Step-height calculated from swelling curve
0.5
180 f 50
174
1.0 2.0
1080 f 200 3610 f 500
1070 3570
Fig. 10. Swelling curves inferred from step-height measurements on annealed Type 316 and 20% cold-rolled Type 316 bombarded with 5 MeV nickel ions at 625°C.
the curve for the annealed Type 316. The step-heights in the cold-worked material are about 35% lower than in the annealed steel, so a distinction can be made between the two swelling curves. We have previously reported [ 161 that swelling is less uniform in a cold-worked steel than in annealed material, reflecting the non-uniformity of cold work. The non-uniformity of swelling is readily apparent in the surface profilometer traces when step-height measurements are made, and an average value of the stepheight can be obtained. This non-uniformity of swelling also manifests itself as increased scatter in TEM data, which can be reduced only by a careful and rather tedious averaging of swellings determined at a number of random locations in the foil. Step-height measurements were not attempted on the specimens irradiated at 575°C because the TEM data indicated that the swellings were too small for accurate measurement by the step-height method, which is limited to swellings above about 3%. The conclusions from the above data are that 20% cold work reduced the swelling at 625°C by about 35% in the damage range of 20 to 280 dpa, and by about 50% at 575°C over the same damage range. The curve in fig. 10 for swelling versus dpa at the peak
W.G.Johnston et al., Annealed and cold-worked type 316 stainlesssteel
swelling temperature for annealed Type 3 16 indicates that the 20% cold-rolled Type 3 16 steel swells about 25% at 155 dpa and about 45% at 230 dpa.
6. Discussion One conclusion of the present work is that the void swelling of Type 3 16 stainless steel does not saturate under all conditions of bombardment by heavy ions, in agreement with McDonald and Taylor [ 151, as well as with the proton work of Keefer, Pard and Kramer [4]. In particular, bombardment with 5 MeV nickel ions at the temperature of maximum swelling produces about 90% swelling at 280 dpa without indication of saturation. The void swellings produced by nickel ions and by fast neutrons at the respective peak swelling temperatures are similar in that the mag nitudes are comparable, as are the void sizes and void densities. This similarity of swelling under the two types of bombardment provides a strong argument for using high dose ion data to guide the extrapolation of reactor data to higher fluences. The resulting predictions for swelling of annealed Type 3 16 at the peak swelling temperature in EBR-II core are 40% at 155 dpa and 70% at 230 dpa. These are unacceptably large swellings for use in commercial reactors. The present intention is to use, not annealed Type 316, but rather, a 20% cold-worked Type 316 in the British PFR and the United States demonstration plant. With regard to cold-worked Type 3 16, our present results are less conclusive. The results indicate that 20% cold reduction by rolling a 125 pm sheet will decrease the swelling produced by nickel ions at the peak swelling temperature of 625’C by about 35 %, which still leads to large swellings. This peak temperature is approximately 115°C higher than the peak swelling temperature in EBR-II, so there remains the possibility that the cold work, being more stable at the lower temperature, will be more effective in reducing the in-reactor swelling. The recent work of Straalsund and Brager [8] has shown that heating cold-worked Type 3 16 at 650°C for a hundred hours essentially removes the beneficial effect of cold-work during subsequent in-reactor exposure at a lower temperature. Given the demonstrated instability of the cold-work effects at 650°C, a temperature that may be encountered in the core of a fast reactor and the
331
large swellings observed at 625°C under nickel ion bombardment, it seems optimistic to expect that coldwork will sufficiently improve the high dose swelling characteristics of Type 3 16 steel to achieve optimum performance to the high fluences that are desired in commercial fast reactors. The large swellings that we have produced by ion bombardment of annealed and cold-worked Type 316 and Type 321 [17], annealed Type 304 [6], and annealed Types 3 18 and 12R72HV [ 171 suggest that this compositional range is not likely to yield a swelling-resistant alloy. The results underscore the need to develop alternate reactor alloys that swell less than these austenitic stainless steels.
Acknowledgements We are grateful to J.J. Jarek for his assistance in this experiment. The 5 MeV nickel ion beam was provided by the Ion Physics Corp., Burlington, Mass., under the direction of W.M. Powers.
References 111 D.J. Mazey, J.A. Hudson and R.S. Nelson, J. Nucl. Mater. 41 (1971) 257.
121 J.A. Hudson, D.J. Mazey and R.S. Nelson, Proc.‘Reading Conf. on Voids Formed by Irradiation of Reactor Materials, ed. Pugh et al., Brit. Nucl. Energy Sot., Harwell (1971) p. 213. [31 G.P. Walters, ref. (21,~. 231. (41 A. Taylor and S.G. McDonald, Radiation-Induced Voids in Metals, ed. J.W. Corbett and L.C. Ianniello, USAEC (1972) p. 499. 151 D.W. Keefer, A.G. Pard and D. Kramer, ref. [4], p. 5 11. 161 W.G. Johnston. J.H. Rosolowski, A.M. Turkalo and T. Lauritzen, J. Nucl. Mater. 47 (1973) 155. 171 W.G. Johnston, J.H. Rosolowski, A.M. Turkalo and T. Lauritzen, J. Nucl. Mater 46 (1973) 273. I81 J.L. Straalsund and H.R. Brager, ANS Transactions 15 (1972) 251. PI J.F. Bates and J.L. Straalsund, HEDL-TME-71-139, Hanford Engrg. Dev. Lab. Richland, Wash. (1971). 1101 R.S. Nelson and D.J. Mazey, Symp. on Radiation Damage in Reactor Materials (IAEA, Vienna, 1969) p. 157. 1111 R. Bullough and R.C. Perrin, Symposium on Irradiation Effects on Structural Alloys for Nuclear Reactor Applications, ASTM Spec. Techn. Pub]. 484 (1970) 317. 1121 D.G. Doran, HEDL-TME-7142, Hanford Engrg. Dev. Lab, Richland, Wash. (1971).
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W.G.Johnston et al., Annealed and cold-worked type 316 stainlesssteel
[ 131 D.G. Doran and G.L. Kulcinski, Radiation Effects 9 (1971) 283. [14] W.K. Appleby and U.E. Wolff, Proc. of Sixth ASTM International Symposium on Effects of Radiation on Structural Materials, Los Angeles (June, 1972) in press. [ 151 S.G. McDonald and A. Taylor, Proc. of Sixth ASTM In-
ternational Symposium on Effects of Radiation on Structural Materials, Los Angeles (June, 1972) in press. [15] W.G. Johnston, J.H. Rosolowski, A.M. Turkalo and K.D. Challenger, Scripta Met. 6 (1972) 999. [ 161 W.G. Johnston, J.H. Rosolowski, A.M. Turkalo and T. Lauritzen, to be published.
NORTH-HOLLAND PUBLISHING COMPANY
NICKEL-ION BOMBARDMENT OF ANNEALED AND COLD-WORKED TYPE 316 STAINLESS STEEL W.G. JOHNSTON, J.H. ROSOLOWSKI and A.M. TURKALO General Electric, Corporate R&D, Schenectady,
New York 12301,
USA
and T. LAURITZEN General Electric Breeder Reactor Department,
Sunnyvale, California 94086,
USA
Received 17 May 1973 Revised manuscript received 2 July 197 3 Bombardment with high doses of 5 MeV nickel ions has produced swellings as high as 90% and 60%, respectively, in annealed and 20% cold-rolled Type 316 steels. The steels contained 15 ppm of cyclotron-injected helium. Swellings were determined by both transmission electron microscopy and by a step-height method that measures the total swelling integrated along the ion path. The swelling in annealed Type 316 has a pronounced peak in the vicinity of 625°C which is about 155°C higher than the peak swelling temperature in-reactor. The magnitudes of the swelling, void densities and void sizes produced in annealed Type 316 by nickel ions and in-reactor at the respective peak swelling temperatures are similar and it is concluded that the nickel ion bombardments provide an acceptable simulation of in-reactor behavior. Using the high dose ion results to guide extrapolation of presently available EBR-II data to higher fluences leads to the prediction that the swelling of annealed Type 316 steel at the peak swelling temperature will reach 40% at 2 X 10z3 n/cm’ (E > 0.1 MeV) in EBR-II core, and 70% at 3 X 10z3 n/cm2. These fluencesin EBR-II correspond to 155 and 230 dpa respectively. Twenty percent reduction by cold-rolling reduces the ion produced swelling by 35% at 625°C and by 50% at 575°C. Le bombardement avec des ions nickel de 5 MeV a fortes doses a produit des gonflements de 90% et 60% dans les aciers type 316 respectivement recuits et ecrouisde 20%. Les aciers contenaient 15 ppm d’hklium inject; au cyclotron. Les gonflements dtaient determines a la fois par microscopic ilectronique en transmission et par une mdthode de hauteur de pas qui permet de mesurer le gonflement total intdgre le long du trajet de l’ion. Le gonflement dans le type 316 recuit presente un pit prononce aux environs de 625”C, qui est d’environ 115°C superieur i la temperature correspondant au pit de gonflement en reacteur. Les amplitudes du gonflement, les densites des vides et les dimensions des vides produits dans le type 316 recuit, soit par les ions nickel, soit en reacteur aux temperatures respectives correspondant au pit de gonflement, sont similaires et iJ est conclu que le bombardement par les ions nickel constitue une simulation acceptable du comportement en rdacteur. L’utihsation des risultats obtenus a l’aide des ions a forte dose pour guider l’extrapolation des donnees disponibles actuellement pour EBR-II ‘ades flux plus eleves:perme\ de prdvoir que le gonflement dans l’acier type 316 recuit. a la tempe’rature du pit de gonflement, atteindra 40% H 2 X 10’ n/cm (E > 0,l MeV) dans le coeur de EBR-II et 70% a 3X 1023n/cm2. Ces fluences correspondent dans le riacteur EBR-II 2 155 et 230 dpa respectivement. 20% de reduction par laminage 3 froid reduisent le gonflement produit par les ions de 35% 5 625°C et de 50% B 575°C. Die Bestrahlung mit einer hohen Dosis 5 MeV Ni-lonen verursacht in warmebehandeltem und 20% kaltverformtem Stahl 316 ein Schwellen von 90 bzw. 60%. Der Stahl enthalt 15 ppm He, das mit einem Zyklotron implantiert wurde. Das Schwellen wurde transmissionselektronenmikroskopisch und nach einer Stufenhohen-Methode bestimmt, nach der der gesarnte, iiber die Spur der lonen integrierte Schwellbetrag gemessen wird. Das Schwellen in wlrmebehandeltem Stahl 316 hat ein ausgeprsgtes Maximum urn 625”C, das etwa 115°C hoher als die Temperatur des Schwellmaximums im Reaktor ist. Der Schwellbetrag, die Porendichte und die Porengrosse, die durch Bestrahlung mit Ni-lonen im Stahl 316 entstehen, sind den Grossen im Reaktor bei der entsprechenden Temperatur des Schwellmaximums Zhnlich. Daraus wird geschlossen, dass die Bestrahlung mit Ni-lonen das Verhahen im Reaktor angemessen simuliert. Die Ergebnisse ermaglichen eine Extrapolation der genenwertig vorliegenden EBR-II-Daten zu h8heren Dosen und die Voraussage, dass das Schwellen von wlrmebehandeltem Stahl 316 im EBR-II-Reaktor bei der Temperatur des maximalen Schwellens 40% bei 2X 1O23 n/cm2 (E > 0,l MeV) und 70% bei 3 X 1O23n/cm2 erreicht. Diesen Dosen entsprechen
W.G.Johnston et al., Annealed and cold-worked type 316 stainlesssteel
331
155 und 230 Verlagerungen pro Atom. Eine 2O%ige Reduktion durch Kaltwalzen erniedrigt das durch Ionenbeschuss verursachte Schwellen bei 625°C urn 35% und bei 575°C urn 50%.
1. Introduction The void swelling behavior of Type 3 16 stainless steel is of particular interest because this alloy has been designated for use as fuel cladding in the British prototype liquid metal fast breeder reactor, (PFR) and in the United States demonstration plant. Both reactors will use cold-worked Type 3 16. At present, there do not exist swelling data at the ultimate fast fluences that are expected in these reactors; but Harwell workers, Mazey, Hudson and Nelson [ 11,have subjected Type 316 steel to carbon ion bombardment up to doses of 400 displacements per atom (dpa). Two results of the Harwell work are that the swelling in solution-annealed Type 316 saturates at less than 15% swelling at 525°C [l] and that cold-worked Type 316 swells somewhat less than the annealed Type 3 16 [2,3]. The work of Taylor and McDonald [4] and of Keefer, Pard and Kramer [5], as well as our own recent work with 5 MeV nickel ion bombardment of Type 304 steel [6] demonstrated conclusively that saturation of swelling at a low value is not a generalcharacteristic of austenitic stainless steel bombarded with energetic particles. We have produced swellings of well over 50% at the peak swelling temperature without indication of saturation. The nickel ion bombardment seemed to provide a good simulation of presently available reactor data on solution-annealed Type 304, and using the high dose ion data to guide extrapolation of the reactor data to higher fluences led to the prediction of about 50% swelling at the peak swelling temperature in EBR-II (about 475°C) at a fluence of 2 X 1023 n/cm2 (E > 0.1 MeV). In the present work, the experimental techniques that were developed and tested on the Type 304 have been applied to Type 316 steel to further investigate the high dose behavior of this material and to learn how prior cold-work affects the swelling at high damage levels under ion bombardment. Two techniques were used for measuring swelling of Type 304; one was conventional transmission electron microscopy (TEM), and the other was a stepheight measurement of the gross swelling [7]. The latter method involves covering the specimen with a partial mask during ion bombardment so that some
regions are bombarded while others are protected. As the bombarded regions swell, the surface becomes elevated and a step forms at the boundary of the masked regions. The height of the step can be measured with a stylus-type profilometer or by interferometry and gives the total swelling integrated along the range of the bombarding particles. The step-height technique is inherently a simple and reliable measurement that can be extended to higher swellings than conventional TEM can measure. At swellings of the Type 304 steel where the two techniques overlapped, the step-height method and TEM measurements were in good agreement. The experimental techniques, including calculation of the damage curve, helium injection, specimen preparation, nickel ion bombardment, examination by TEM, and measurement of step-heights have been described in detail [6] and will not be further discussed in this paper. The approach to the investigation of the solutionannealed Type 316 has been the same as that which we pursued with the Type 304 steel. The temperature dependence of void swelling was determined, and the dose dependence of the swelling at the peak swelling temperature was measured. The results of ion bombardments will be compared with data on in-reactor behavior, and we shall use the high dose ion data to guide extrapolation of the reactor data to the higher fluences that are of interest. The swelling behavior of 20% cold-worked Type 3 16 will be compared with that of the solution-annealed steel from the same heat. At the outset, we recognize a complication in doing heavy ion bombardments of the cold-worked steel. By necessity, the heavy ion damage, which results from very high displacement rates, must be carried out at a higher temperature than the corresponding in-reactor bombardments. This presents the possibility that the higher temperatures in the ion bombardment experiments may anneal some of the cold work. The possibility of annealing seems particularly strong in view of the recent work of Straalsund and Brager [8] who showed that the beneficial effect of cold-work in reducing in-reactor swelling of Type 3 16 was lost in 100 h at 650°C.
W.G. Johnston
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et al., Annealed and cold-worked
2. TEM measurements of swelling of annealed Type 316 steel The commercial Type 3 16 steel, with the composition given in table 1, was annealed in vacuum at 1010 “C for one hour and rapidly cooled in argon. Specimens about 125 pm thick and 3 mm in diameter, containing 15 atomic ppm of helium, injected uniformly with a cyclotron, were electropolished and bombarded with 5 MeV nickel ions [6]. The flux of nickel ions was - 1.3 X 1013 ions/cm*. set which corresponds to a displacement rate of approx&ately 2 X lOA dpa/ set at the peak damage region where foils were taken for TEM analysis. The method for determining the position of the TEM foils along the range of the bombarding ions has been described [6]. The void densities and sizes were determined from stereoscopic pairs of electron micrographs taken at 100 kV. The swelling is reported as A V/V, = A V/( V - A V), where A V is the void volume in a foil of volume, V.
I
7
I
1
I
I
I
I
TYPE 316 ANNEALED
/
1
1
,/---\
/’ ’ -REAcTwt 6.7
type 316 stainless steel
Table 1 Analysis of Type 3 16 steel in weight percent Cr Ni MO Mn Si cu co
C N P s B Nb Ti Fe
17.03 13.18 2.10 1.83 0.72 0.14 0.13
0.055
0.036 0.017 0.008 0.0015 < 0.02 < 0.02 balance
The temperature dependence of void swelling as measured by TEM is shown in fig. 1. There is a maximum in the swelling at about 625°C. The temperature dependence of swelling in the core of EBR-II as given by the empirical expression of Bates and Straalsund [9] is shown by the curve on the left in fig. 1. The peak swelling temperature for the ion bombardment is about 115°C higher than the peak swelling temperature in-reactor. In order to investigate the greatest swelling that will occur in Type 3 16 steel, the dose dependence of ion-produced swelling was measured at the peak swelling temperature, 625’C, and the results are shown in fig. 2. At the highest damage level of about 230 dpa, the swelling was about 50%. Also shown in fig. 2 is
‘\
x lo**“/cM* (FAST)
TYPE 316 625’C 15
ppm He PJ
i
ION BDMBARDYENT
D.lL 400
,
I 500
600
,
,
-
700
TEMPERATURE, ‘C
Fig. 1. Temperature dependence of swelling in annealed Type 316 stainless steel bombarded with 5 MeV nickel to a damage level of 67 dpa. The steel contained 15 ppm of cyclotron-injected helium. The temperature dependence of EBR-II Core swelling [7] is shown by the dashed curve.
D.ll ’ “I” 4
I 100
IO DISPLACENEWTS
L I,II IDOD
PER ATOY
Fig. 2. Dose dependence of ion-produced swelling in annealed Type 316 steel at the peak swelling temperature of 625’C.
W.G.Johnston et al., Annealed and cold-worked type 316
stainlesssteel
333
625.C *Ii.
625% r/oHa I
100
lo’3L
DISPLACEMENTSPER ATON
Fig. 3. Average void diameters in ion-bombarded annealed Type 316. the dose dependence of swelling for helium-free steel at 625°C. It should be noted that we have previously pointed out the limitations of TEM at 100 kV in measuring large swellings and large void sizes [6]. The void sizes and densities measured in order to determine the swellings of annealed Type 316 are shown in figs. 3 and 4. The void sizes increase monotonically with dose, while the void densities increase at low doses and pass through a maximum. The maximum in the void density seems to correlate with the amount of swelling rather than with the damage level. We have observed in several alloys that the void density maximum occurs at 6 to 10% swelling. The arrows in fig. 4 indicate the doses at which 6% swelling is achieved in the three caSes shown. At 6% swelling the average spacing of voids is twice the void diameter, assuming a uniform void size in order to simplify the calculation. The swelling is appreciably less in helium-free Type 3 16 than in the helium-injected steel bombarded at the same temperature, and the difference is due to the much lower void densities in the absence of helium. This large effect of helium on void nucleation,‘which was also seen in Type 304 steel [6], was first reported by Nelson and Mazey [ lo]. 3. Step-height measurements of swelling in annealed Type 316 Helium-injected
specimens of annealed Type 3 16
IO
I
I ’ I
I
1111’
I
,
1000
100
DISPLACEMENTSPER ATOM
Fig. 4. Void densities in ion-bombarded annealed Type 316. steel were partially masked and bombarded with 5 MeV nickel ions at 625°C. The step height at the boundary of the unirradiated region and the elevated, irradiated region was measured with a stylus-type profilometer [7]. The results are presented in table 2 for several ion doses. Each reported step-height is the average of eight measurements at different locations on one specimen. The measurements have been corrected for the amount of nickel injected during born-: bardment. The step height due to surface elevation is a measure of the total integrated swelling along the range of the bombarding ions. From the step-heights at several ion doses and the damage curve for nickel
Table 2 Step-heights on annealed Type 316. Step-height calculated
Ion dose
Measured step-height
(lO”/cm’)
(A)
from swelling curvea)
0.5 1.0 2.0
290 f 50 1700 f 1.50 5500 f 400
298 1660 5530
akhe swelling curve was inferred from the step-height data. The calculated step-heights merely indicate how well the curve has been constructed.
W.G. Johnston
et al., Annealed and cold-worked type 316 stainless steel
0 x
-
-
STEPHEWtlT DATA
/
xx
i
l9
INFERRED FROM STEP HEIGHTS x
x
-4w-540% ION-TEY 6a’C CNNvEFnDmnN
TEY DATA
0
x 0
x
0
011 .IO
ID0
1000
DISPLACEMENTS PER ATOM
0.1
I
1
J
x I
,,,,,,I
IO= NEUTRONSlCY2
lO23 (E>O.I
lo2’
NIV)
F&S. Swelling curve for annealed Type 316 inferred from step-height measurements. TEM data points are shown for comparison.
Fig. 6. Comparison of EBR-II [7] and nickel ion-produced swellings in annealed Type 3 16 at the respective peak swelling temperatures.
ions in stainless steel, it is possible to deduce the swelling versus dpa curve shown in fig. 5 [6]. As a check, the swelling curve can be used to predict the step-height values, and the agreement between the calculated and observed step-height in table 2 is an indication of how well the curve has been constructed. Also plotted in fig. 5 are the data points for swelling versus dpa as determined by TEM. Comparison of the curve and the TEM data points indicates that the swelling as determined by step-height measurements is slightly larger than that determined by TEM. The step-height measurement [7] is inherently a more simple, direct and reliable measurement of total swelling than is the TEM measurement, so we tend to place more credence in the result of step-height measurements.
a theoretical calculation of how the temperature should scale with atom displacement rate. However, in the absence of firm experimental verification of such calculations, we prefer to follow the empirical approach we took in the work on Type 304 [6]. As shown in fig. 1, the peak swelling temperature for the ion bombardments was about 115°C higher than for in-reactor swelling. In order to compare the maximum swellings for the two types of data, we shall compare the swellings at the peak swelling temperatures. The ion data at 625°C will be compared with EBR-II swelling data in the temperature range of 5 10°C + 30°C. We select the reactor data in a temperature range because there do not exist sufficient data at one single temperature. In comparing the damage produced by fast neutrons with that due to heavy ions, we shall use the conversion of 1O23 n/cm* (E > 0.1 MeV) equivalent to 77.4 dpa. This conversion is taken from the calculations of Doran [ 12,131 for EBR-II core, as discussed in ref. [6]. A comparison of in-reactor swelling with ion bombardment results determined by TEM and by stepheight measurements is presented in fig. 6. The reactor data are from the compilation of Bates and Straalsund [9] which includes data of a number of investi-
4. Comparison of ion bombardment results with inreactor swelling of annealed Type 316 steel In order to compare in-reactor swelling with swelling produced by heavy ions it is necessary to properly scale the temperatures in the two cases, and to relate the damage levels produced by ions to those produced by fast neutrons. Bullough and Perrin [ 1 l] have made
W.G. Johnston
et al., Annealed and cold-worked
FLUENCE, n/cm*
FLUENCE, n/cm* 102’
,
I
X
REACTOR, 460’-540’C
: Y a P s
0
_
o
0
u s
I
X/ X
0
_
1 I111811 1023 I
X IONS. 625’C
X’
IONS, 625’C
;lOOO--
I
TYPE 316 0 REACTOR, 480e-540.C
- TYPE 316 _ 0
335
type 316 stainless steel
x
f
\
0
8
xX
0
d %
o/Xxx
0
:
\
i ‘0%
,
I
I31III 100 CWLACEMENTS PER ATOM
Id’,,
/ X
X
I
100 DISPLACEMENTS PER ATOM
Fig. 7. Comparison of void sizes produced in annealed Type 316 in EBR-II [ 141 and by ion-bombardment at the respective peak swelling temperatures.
Fig. 8. Comparison of void densities produced in annealed Type 316 in EBR-II [ 141 and by ion-bombardment at the respective peak swelling temperatures.
gators. The solid curve was obtained from our stepheight measurements and the X’s are TEM data points, both on nickel ion bombarded specimens. The stepheight curve is closer to the reactor data than are the TEM points, but both show swellings that are on the low side of the reactor results. The slope of the reactor and ion data are similar in the fluence range where they overlap, and as the ion data continue to high damage levels and swellings, they should provide a conservative prediction of in-reactor swelling at higher fluences. The similarity of the swelling produced by ions and in-reactor at comparable damage levels is further borne out in the comparison of void sizes and densities [ 141 for the two cases, presented in figs. 7 and 8. Although the magnitudes of the ion and neutron produced swellings compared in the above manner do not agree as well as they did for annealed Type 304 [6], the agreement is sufficiently good, particularly in view of the similarity of void sizes and densities, to conclude that the ion bombardment provides an acceptable simulation of the reactor damage, and that thehigh dose ion data can be used to guide extrapolation of reactor data to higher fluences. An extrapolation of in-reactor data based on our high dose nickel ion results indicates that the swelling in annealed Type 3 16 at the peak swelling temperature in EBR-II core should reach about 40% at a fluence of 2 X 1023 n/cm2 (E > 0.1 MeV) and about 70%
at 3 X 1O23n/cm2. (These fluences correspond to 155 and 230 dpa respectively.) We judge these to be conservative extrapolations of the reactor data, since the ion-produced swellings lie lower than the reactor data in fig. 6. 5. Swelling of 20% cold-worked Type 3 16 Solution-annealed Type 3 16 steel from the heat described in table 1 was cold-rolled 20 + 2% from a foil thickness of 125 pm. The 20% reduction of the thin foil could not be accomplished in a single rolling pass, but required several passes. Therefore, the coldworked structure may differ from that produced by a single 20% deformation, (such as in cold-drawn seamless cladding tubes). Following the cold-work, helium was injected uniformly into the foil to produce a concentration of 15 atomic ppm. Nickel ion bombardments were carried out at 575°C and 625°C and the TEM measurements of swelling are shown in fig. 9. Prior to the ion bombardments, the specimens were heated to 25°C above the subsequent bombardment temperature for a period of between 15 and 30 min as part of an outgassing procedure. The most extreme annealing in the present work would have occurred in one-half hour at 65O’C followed by 4: h at 625°C during the actual bombardment. For the lower temperature runs, the most extreme (annealing was 1 h at 600°C followed by 41 h at 575°C.
336
W.G. Johnston
et al., Annealed and cold-worked type 316 stainless steel
U6PLACEmTS PER ATOM (626-C) d’00j
STEP HENIT
I. IO
DATA
100
500
DISPLACEMENTSPER ATOM DISPLACEMENTSPER ATOM (575'Cl
Fig. 9. Swelling determined by TEM in annealed Type 316 and 20% cold-rolled Type 316, bombarded with 5 MeV nickel ions Note that the upper abscissa scale refers to the 625°C data and the lower scale refers to the 575°C data.
The TEM data in fig. 9 show appreciable scatter for swelling at 575°C; nevertheless, it appears that the cold-work has resulted in a reduction of about 50% in the swelling. At 625’C, the solution annealed and cold-worked data appear similar; the scatter is sufficient to mask a relatively small effect of the coldwork, such as that reported from step-height measurements in the following paragraph. Step-height measurements of the swelling produced in cold-worked Type 3 16 at 625°C gave the results listed in table 3; and the swelling versus dpa curve constructed from the data is shown in fig. 10, along with Table 3 Step-heights on cold-worked Type 316.
Ion dose (101’/cm2)
Measured step-height (A)
Step-height calculated from swelling curve
0.5
180 f 50
174
1.0 2.0
1080 f 200 3610 f 500
1070 3570
Fig. 10. Swelling curves inferred from step-height measurements on annealed Type 316 and 20% cold-rolled Type 316 bombarded with 5 MeV nickel ions at 625°C.
the curve for the annealed Type 316. The step-heights in the cold-worked material are about 35% lower than in the annealed steel, so a distinction can be made between the two swelling curves. We have previously reported [ 161 that swelling is less uniform in a cold-worked steel than in annealed material, reflecting the non-uniformity of cold work. The non-uniformity of swelling is readily apparent in the surface profilometer traces when step-height measurements are made, and an average value of the stepheight can be obtained. This non-uniformity of swelling also manifests itself as increased scatter in TEM data, which can be reduced only by a careful and rather tedious averaging of swellings determined at a number of random locations in the foil. Step-height measurements were not attempted on the specimens irradiated at 575°C because the TEM data indicated that the swellings were too small for accurate measurement by the step-height method, which is limited to swellings above about 3%. The conclusions from the above data are that 20% cold work reduced the swelling at 625°C by about 35% in the damage range of 20 to 280 dpa, and by about 50% at 575°C over the same damage range. The curve in fig. 10 for swelling versus dpa at the peak
W.G.Johnston et al., Annealed and cold-worked type 316 stainlesssteel
swelling temperature for annealed Type 3 16 indicates that the 20% cold-rolled Type 3 16 steel swells about 25% at 155 dpa and about 45% at 230 dpa.
6. Discussion One conclusion of the present work is that the void swelling of Type 3 16 stainless steel does not saturate under all conditions of bombardment by heavy ions, in agreement with McDonald and Taylor [ 151, as well as with the proton work of Keefer, Pard and Kramer [4]. In particular, bombardment with 5 MeV nickel ions at the temperature of maximum swelling produces about 90% swelling at 280 dpa without indication of saturation. The void swellings produced by nickel ions and by fast neutrons at the respective peak swelling temperatures are similar in that the mag nitudes are comparable, as are the void sizes and void densities. This similarity of swelling under the two types of bombardment provides a strong argument for using high dose ion data to guide the extrapolation of reactor data to higher fluences. The resulting predictions for swelling of annealed Type 3 16 at the peak swelling temperature in EBR-II core are 40% at 155 dpa and 70% at 230 dpa. These are unacceptably large swellings for use in commercial reactors. The present intention is to use, not annealed Type 316, but rather, a 20% cold-worked Type 316 in the British PFR and the United States demonstration plant. With regard to cold-worked Type 3 16, our present results are less conclusive. The results indicate that 20% cold reduction by rolling a 125 pm sheet will decrease the swelling produced by nickel ions at the peak swelling temperature of 625’C by about 35 %, which still leads to large swellings. This peak temperature is approximately 115°C higher than the peak swelling temperature in EBR-II, so there remains the possibility that the cold work, being more stable at the lower temperature, will be more effective in reducing the in-reactor swelling. The recent work of Straalsund and Brager [8] has shown that heating cold-worked Type 3 16 at 650°C for a hundred hours essentially removes the beneficial effect of cold-work during subsequent in-reactor exposure at a lower temperature. Given the demonstrated instability of the cold-work effects at 650°C, a temperature that may be encountered in the core of a fast reactor and the
331
large swellings observed at 625°C under nickel ion bombardment, it seems optimistic to expect that coldwork will sufficiently improve the high dose swelling characteristics of Type 3 16 steel to achieve optimum performance to the high fluences that are desired in commercial fast reactors. The large swellings that we have produced by ion bombardment of annealed and cold-worked Type 316 and Type 321 [17], annealed Type 304 [6], and annealed Types 3 18 and 12R72HV [ 171 suggest that this compositional range is not likely to yield a swelling-resistant alloy. The results underscore the need to develop alternate reactor alloys that swell less than these austenitic stainless steels.
Acknowledgements We are grateful to J.J. Jarek for his assistance in this experiment. The 5 MeV nickel ion beam was provided by the Ion Physics Corp., Burlington, Mass., under the direction of W.M. Powers.
References 111 D.J. Mazey, J.A. Hudson and R.S. Nelson, J. Nucl. Mater. 41 (1971) 257.
121 J.A. Hudson, D.J. Mazey and R.S. Nelson, Proc.‘Reading Conf. on Voids Formed by Irradiation of Reactor Materials, ed. Pugh et al., Brit. Nucl. Energy Sot., Harwell (1971) p. 213. [31 G.P. Walters, ref. (21,~. 231. (41 A. Taylor and S.G. McDonald, Radiation-Induced Voids in Metals, ed. J.W. Corbett and L.C. Ianniello, USAEC (1972) p. 499. 151 D.W. Keefer, A.G. Pard and D. Kramer, ref. [4], p. 5 11. 161 W.G. Johnston. J.H. Rosolowski, A.M. Turkalo and T. Lauritzen, J. Nucl. Mater. 47 (1973) 155. 171 W.G. Johnston, J.H. Rosolowski, A.M. Turkalo and T. Lauritzen, J. Nucl. Mater 46 (1973) 273. I81 J.L. Straalsund and H.R. Brager, ANS Transactions 15 (1972) 251. PI J.F. Bates and J.L. Straalsund, HEDL-TME-71-139, Hanford Engrg. Dev. Lab. Richland, Wash. (1971). 1101 R.S. Nelson and D.J. Mazey, Symp. on Radiation Damage in Reactor Materials (IAEA, Vienna, 1969) p. 157. 1111 R. Bullough and R.C. Perrin, Symposium on Irradiation Effects on Structural Alloys for Nuclear Reactor Applications, ASTM Spec. Techn. Pub]. 484 (1970) 317. 1121 D.G. Doran, HEDL-TME-7142, Hanford Engrg. Dev. Lab, Richland, Wash. (1971).
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[ 131 D.G. Doran and G.L. Kulcinski, Radiation Effects 9 (1971) 283. [14] W.K. Appleby and U.E. Wolff, Proc. of Sixth ASTM International Symposium on Effects of Radiation on Structural Materials, Los Angeles (June, 1972) in press. [ 151 S.G. McDonald and A. Taylor, Proc. of Sixth ASTM In-
ternational Symposium on Effects of Radiation on Structural Materials, Los Angeles (June, 1972) in press. [15] W.G. Johnston, J.H. Rosolowski, A.M. Turkalo and K.D. Challenger, Scripta Met. 6 (1972) 999. [ 161 W.G. Johnston, J.H. Rosolowski, A.M. Turkalo and T. Lauritzen, to be published.