電子輻照對純鐵位錯環(huán)的影響

1、Evolution of irradiation damage under electron irradiation in deuterium-ion implanted pure iron*S.N. Jianga, F.R. Wana,*, Y.Longa, J.C. Hea, Y.Y. Zhua, S.Shia, S.W. Yanga, Q.Zhana, S.Wangb, S.Ohnukiba School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing

2、100083, Chinab Faculty of Engineering, Hokkaido University, Sapporo 060-8628, JapanABSTRACT: The evolution of irradiation damage in thin foils of pure iron has been investigated. Pure iron implanted deuterium ions at room temperature was aged at 773K for 1h, then irradiated by electrons at 773K usin

3、g High Voltage Electron Microscope (HVEM). The result shows that the vacancy loops would shrink and disappear with the increasing of irradiated dose. Compared with the vacancy loops in the case of hydrogen, the shrinkage rate in the case of deuterium is lower due to the lower bias strength of the di

4、slocation loops. Keywords: Deuterium; Irradiation damage; Dislocation loop; Vacancy* Project supported by the National Natural Science Foundation of China ( Grant No. 50971030), the Natural Basic Research Program of China (Grant No. 2009 GB109004 and 2011GB108004). * Author for correspondence, wanfr

5、1. Introduction The challenging environment of structural materials for fusion reactor is severe. A key problem is how to resist the irradiation neutron with a energy up to 14MeV. The dislocation effect caused by neutron irradiation would produce a large number of primary knock-on atoms(PKA), then c

6、ollision cascade, accompanying a lot of spot defects whose evolution and aggregation is the main reason for irradiation damage. Meanwhile intense production of transmutant elements (in particular, hydrogen and helium) has great impact on the mechanical properties of structural materials. The presenc

7、e of hydrogen or helium would have great influence on irradiation of performance in materials. Helium will precipitate as bubbles at grain boundary which will lead to embrittlement1. There are systematic works on the interaction between He and irradiation defects2,3, while not so many on hydrogen4.

8、Another specificity environment for fusion reactor sturctural materials is the existence of triterium. Due to its radioactivity, it is difficult to research the interaction between triterium and irradiation damage. However, it may be possible to explore the effect of triterium from the isotopic effe

9、ct between hydrogen and deuterium on irradiation damage. For the isotopic atoms of hydrogen, deuterium, there is only a few simulation works5. This paper focuses on irradiation damage in pure iron implanted deuterium. Furthermore, the relationship between pure iron implanted deuterium and that impla

10、nted hydrogen may be revealed. This may provide experimental data to irradiation damage for fusion reactor sturctural materials.2. Experimental The specimens for ion implantation and electron irradiation were TEM disks. The disks with 3 mm in diameter were punched out from a 0.1 mm thick strip which

11、 was prepared from a thick plate of pure iron (99.9995%) by spark cutting and milled to final thickness. Then they were heat treated (1023K / 1h / water-cooled) to remove stain effect. The final TEM specimens were polished by twin-jet electro-polisher using 5% HCLO4-95%C2H5OH polishing solution.Deut

12、erium ions implantation was carried out by LC-4 high energy ion implantation apparatus. Implanted ions were D2+. Implanted dose was 1×1017 D+ / cm2 under the conditions of 3.3 × 10-6 vacuum and 58 keV accelerating voltage at room temperature. The penetration depths of 58 keV D2+ in pure ir

13、on was estimated to be about 500 nm by TRIM computer code to achieve thickness distribution for TEM experiment.After deuterium implantation, the specimens were aged at 773 K for 1 h so that dislocation loops could grow up into large size for electron irradiation. Finally electron irradiation was per

14、formed by JEOL-1300 high voltage electron microscope at 773 K. The electron accelerating voltage was 1250 kV and the damage rate of electron irradiation was 5.5 × 10-4 dpa / s.3. Results and discussionFig.1 shows microstructures of pure iron before and after deuterium implantation at room tempe

15、rature observed by H-800 low-voltage TEM. Before implanting deuterium, There is no obvious defects. Contrast to that without implanted deuterium, the specimen implanted deuterium formed a large number of defects. These defects were usually small dislocation loops with a high number density. Moreover

16、, they appears as black spots in TEM photoes. Deuterium atoms implanted in pure iron would be captured by these defects and existed in the specimen steadily. (a) (b) Fig. 1 Microstructure of pure iron before and after deuterium implanted(a) before deuterium implanted; (b) after deuterium implanted.A

17、fter aged at 773K, the high-density and small-size defects formed by deuterium implantation would accumulate mutually, and then grow up into low-density and large-size dislocation loops. Under electron irradiation in HVEM, these large dislocation loops would further absorb point defects produced by

18、electron irradiation.Fig.2 shows the evolution of the large dislocation loops during electron irradiation at 773 K. In-situ observation was made under double-beam diffraction condition. Large dislocation loop formed in deuterium, implanted and followed by aging at 773 K for 1 h (0 dpa). This means t

19、he number density of dislocation loops during aging at 773 K became gradually low while the size increased. Under electron irradiation, the large dislocation loop shrinked with increasing irradiation dose.0dpa 0.05dpa 0.28dpa0.32dpa 0.35dpa 0.38dpa 0.42dpaFig. 2 Evolution of dislocation loops in deu

20、terium implanted iron during electron irradiation at 773 KElectron irradiation would produce a lot of Frenkel pairs, i.e. interstitial atoms and vacancies. Usually, interstitial atoms is much easier to diffuse and accumulate than vacancies because of their high mobility6. As a result, much more inte

21、rstitial atoms are absorbed by dislocation than vacancies. When absorbing interstitial atoms, interstitial dislocation loop (i-loop) grows up, while vacancy dislocation loop (v-loop) shrink. Therefore, it is reasonable to judge that the nature of the large dislocation loops observed in this paper is

22、 of vacancy type loops 7. 0.31dpa 0.44dpa 0.60dpa 0.70dpa 0.84dpa 1.00dpaFig. 3 Evolution of dislocation loops in deuterium implanted iron during electron irradiation at 773 KFig.3 shows the evolution of dislocation loops in deuterium implanted iron during electron irradiation at 773 K. In the same

23、way, the shrinkage and disappear- rance of v-loops under electron irradiation were observed. An irradiation dose of 0.69 dpa is needed for v-loops disappearance, much higher than the case (0.45dpa) of hydrogen ion implantation8. Besides, a growing dislocation loop was observed by the side of shrink-

24、 ing v-loops (showed by arrows). As mentioned in many papers9, i-loops would form and grow up gradually under single electron irradiation.During the formation of irradiation damage, it is important for dislocation loops to absorb which natures of point defects (interstitial atom or vacancy). A bias

25、strength parameter S is often used to express the difference between the two kinds of reaction to point defects. The formula is shown as follows: Where, Zid、Zvd means the interaction strength of a dislocation loop to a interstitial atom and vacancy, respectively. According to the formula, a loop wit

26、h larger bias strength would absorb more interstitial atoms than vacancies during irradiation. As a result, more and more vacancies are left, and then accumulate together to form void along the direction of three dimentions when the vacancy concentration is supersaturated. Then so-called “irradiatio

27、n swelling” arises which would deteriorate maretials, for example embrittlement and descend of ductility. Ultimately, void would affect the operating life of materials. Larger bias strength means larger irradiation swelling in materials. So less bias strength is favourite. Irons with hydrogen8 and d

28、euterium implanted (Fig.2) at room temperature then was carried out electron irradiation at the same conditions were compared with each other. Fig.4 shows the relationship between loop size and irradiated dose of the two iron specimens.Fig. 4 The size of dislocation loop as a function of irradiated

29、dose both in hydrogen and deuterium-implanted irons in the same irradiation conditionFrom this figure, the shrinkage rate of dislocation loop in deuterium-implanted iron is lower than that in hydrogen-implanted iron. It illustrates that bias strength of v-loops in deuterium-implanted iron is less th

30、an that in hydrogen-implanted iron. It may summarize a conclution that iron implanted deuretium has superior resistence of irradiation swelling than that implanted hydrogen. From the isotopic effect of hydrogen, deuterium and triterium, it could be suggested that tritium may have the weakest bias st

31、rength among the three hydrogen isotope atoms. This message may provide referential value to research on irradiation damage of fusion reactor structural materials. 4. SummaryThe v-loops could form in iron implanted by deuterium. Such kind of loops absorbs more interstitial atoms than vacancies and w

32、ould shrink to disappear during electron irradiation. The shrinkage rate of loops with deuterium is lower than that with hydrogen. It suggested that the loops with deuterium have weaker bias strenghth than that with hydrogen due to isotopic effect. References1 F. R. Wan. Irradiation damage of metal. Beijing. Science Press. (1993) 144.2 E. H. Lee, J. D. Hum, T. S. Byun, et al. Effect of helium on radiation-induced defect microstructure in austenitic stainless steel. J. Nucl. Mater. 280 (2000) 18-24.3 I. I. Chernov, A. N. Kalashnikov, B. A.