Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://danp.sinp.msu.ru/LIIWM/Mashkova_NIMBInPress_ErosionC-Fiber.pdf Äàòà èçìåíåíèÿ: Thu Feb 10 22:04:07 2011 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 22:37:22 2012 Êîäèðîâêà: ISO8859-5

Nuclear Instruments and Methods in Physics Research B xxx (2011) xxx-xxx

Contents lists available at ScienceDirect

Nuclear Instruments and Methods in Physics Research B
journal h omepage: www.else vier.com/locate/nimb

Erosion of carbon fiber composites under high-fluence heavy ion irradiation
Natalya N. Andrianova a, Anatoly M. Borisov a, Eugenia S. Mashkova a,, Yury S. Virgiliev
a b

b

Institute of Nuclear Physics, Moscow State University, 119991 Moscow, Russia NIIgraphite, 111141 Moscow, Russia

article

info

abstract
The ion-induced erosion, determining by sputtering yield Y and surface evolution including structure and morphology changes of the modified surface layers, of two commercial carbon fiber composites (CFC) with different reinforcement - KUP-VM (1D) and Desna 4 (4D) have been studied under 30 keV Ar+ high fluence (ut $ 1018-1020 ion/cm2) irradiation in the temperature range from room temperature to 400 ÀC. Ion-induced erosion results in the changes of carbon fiber structure which depend on temperature and ion fluence. Monitoring of ion-induced structural changes using the temperature dependence of ion-induced electron emission yield has shown that for Desna 4 and KUP-VM at dynamic annealing temperature Ta % 170 ÀC the transition takes place from disordering at T < Ta to recrystallization at T > Ta. The annealing temperature Ta is close to the one for polycrystalline graphites. Microscopy analysis has shown that at temperatures T < Ta the etching of the fibers results in a formation of trough-like longitudinal cavities and hillocks. Irradiation at temperatures T > Ta leads to a crimped structure with the ribs perpendicular to fiber axis. After further sputtering of the crimps the fiber morphology is transformed to an isotropic globular structure. As a result the sputtering yield decreases for Desna 4 more than twice. This value is almost equal to that for KUP-VM, Desna 4, polycrystalline graphites and glassy carbons at room temperature. ã 2011 Published by Elsevier B.V.

Article history: Received 30 July 2010 Received in revised form 15 November 2010 Available online xxxx Keywords: Carbon fiber composites (CFC) High fluence ion irradiation Sputtering Ion-induced erosion Ion-induced electron emission Radiation damage

1. Introduction Carbon fiber composites consisting of reinforcing carbon fibers embedded in a carbon or graphite matrix are widely used in nuclear reactors, thermonuclear facilities, and aerospace industry due to their strength, heat shielding properties, and a number of other specific characteristics [1]. Carbon fibers consist of a low-perfection core, similar in structure to glassy carbon, and a structurally perfect, textured shell, formed by graphite layers similar to those in pyrolytic graphite, with their basal planes parallel to the fiber axis and their c axis lying in radial directions. The ion-induced kinetic processes controlling surface evolution (erosion) are mainly sputtering processes and diffusion [2,3]. The problems of erosion of the CFC surface layers under light ion irradiation in thermonuclear devices [4,5] and under oxygen irradiation of the spacecrafts and rockets have been studied intensively [6]. The interactions of the heavier ions of the noble gases with carbon-carbon materials have been insufficiently investigated. Investigations of the structure and morphology of the ion-induced surface layer of one-dimensional CFC KUP-VM under high 30 keV N? ion irradiation showed that irradiation results in a loss of 2 anisotropy of the KUP-VM surface layer structure. This is because
Corresponding author. Tel.: +7 495 939 4167; fax: +7 495 939 0896.
E-mail address: es_mashkova@mail.ru (E.S. Mashkova). 0168-583X/$ - see front matter ã 2011 Published by Elsevier B.V. doi:10.1016/j.nimb.2010.12.063

of amorphization at room temperature or recrystallization at a temperature higher than a dynamic annealing temperature Ta when fiber crimping had been observed [7,8]. Almost all types of radiation influence lead to temperature-depended structural changes of carbon-carbon materials. Significant effects of radiation damage are observed at temperatures close to room temperature (RT). With increasing temperature a radiation defect mobility results in the complex processes of dynamic annealing [9,10]. For many carbon-based materials with increasing target temperature under intensive high fluence tens keV ion irradiation at normal incidence, a step-like increase (jump) of ion-induced electron emission yield c at a dynamic annealing temperature Ta takes place. These temperature dependences of ion-induced electron emission yield c has been used for in situ monitoring the ion-induced structure changes [11,12]. The aim of the present work is the study of regularities of surface erosion of CFC with different fibers architecture under high fluence argon ion irradiation. 2. Experimental The experiments of ion irradiation by 30 keV Ar+ have been carried out on the mass-monochromator of the Institute of Nuclear Physics, Moscow State University [13]. The 5-35 keV ion beam was produced in an arc source with a longitudinal magnetic field.

Please cite this article in press as: N.N. Andrianova et al., Erosion of carbon fiber composites under high-fluence heavy ion irradiation, Nucl. Instr. and Meth. B (2011), doi:10.1016/j.nimb.2010.12.063


2

N.N. Andrianova et al. / Nuclear Instruments and Methods in Physics Research B xxx (2011) xxx-xxx

The ions were separated and the beam was focused by a Siegbantype magnetic sector field. The target holder permitted the variation of the angle h of ion incidence from 0o to 89o and the target temperature from Ð180 to 1000 ÀC. The samples for the investigation were commercial CFC materials with different reinforcement KUP-VM (1D) and Desna 4 (4D) produced by NIIgraphite (Moscow, Russia) and had the shape of rectangular plates. The base of 1D one-directional carbon composite KUP-VM is a VMN-4 polyacrylonitrile (PAN) fibers. The 4D-reinforced composite Desna 4 with a specific architecture of three-dimensional reinforced orthogonal framework complementary bonding by one of the diagonal. It is based on PAN fibers (UKN-5000 ones) with a matrix prepared via multiple pitch-impregnation cycles. For comparison the samples of polycrystalline graphite MPG-8 were also irradiated. The experimental procedure is described elsewhere [7,8]. Irradiation was produced by 30 keV Ar+ ions. Ion current was $0.4 mA/cm2, the cross-section of ion beam was 0.3 cm2. The total ion fluences were 1018-1020 ion/cm2. The temperature dependences of ion-induced electron emission yield c were used for in situ monitoring the ion-induced structure changes [11]. The value of c was determined as the ratio of the electron current to the primary ion one with the instrument error $2.5%. Sputtering yields Y were determined by weight loss measurements. The error of the weight measurements was 0.02 mg. The loss of weight was not smaller than 0.2 mg. Investigations of the samples before and after irradiation included analysis of surface topography by scanning electron microscopy (SEM) using LEO-1430vp, optical microscope Axiostar plus and laser goniophotometry (LGF) technique [14,15]. The crystalline structure of the surface layers was analysed by the method of Reflection High Energy Electron Diffraction (RHEED) in EMR-102 (Russian model) operated at 50 kV and an electron beam current of 50 lA. 3. Results and discussion The temperature dependences of the ion-induced electron emission yield c(T) under of 30 keV Ar+ irradiation at normal ion incidence of the samples of Desna 4 (4D) and KUP-VM (1D) cut out parallel to the fibers are presented in Fig. 1. One can see that the measured data demonstrate a step-like increase (jump) of ion-induced electron emission yield c at a dynamic annealing temperature Ta % 170 ÀC. According to RHEED patterns this temperature divides the amorphous state of irradiated target at T < Ta

Fig. 1. The temperature dependences of c for polycrystalline MPG-8, CFC Desna 4 and KUP-VM.

from the polycrystalline state at T > Ta. At temperature T < Ta the diffraction patterns exhibited an amorphous halo. At elevated temperatures for KUP-VM the diffraction patterns obtained in the measurements along and across carbon fibers virtually do not differ from one another and are a system of three slightly smeared rings typical for isotropic polycrystalline graphites, as in the case of 30 keV N? irradiation [8]. One should note that in the case of 2 Desna 4, due to its specific architecture, both the fibers recumbent on the sample surface and the fibers arranged perpendicular to the sample surface (i.e., the butt-ends of the fibers) are simultaneously irradiated. The comparison with the temperature dependence c(T) measured for isotropic polycrystalline graphite MPG-8 demonstrates just small difference in the Ta value, see Fig. 1. So, the similarity of c(T)-dependences for KUP-VM and Desna 4 shows that the high-fluence Ar+ ion irradiation results, as in the case of nitrogen irradiation of KUP-VM, in the loss of anisotropy of the surface layer structure, namely, disordering at the room temperatures (T < Ta) and recrystallization at the temperature higher than Ta. The analysis of KUP-VM and Desna 4 surface topography using SEM and optical microscopy has shown that, as in the case of 30 keV N? - KUP-VM [7,8], Ar+ irradiation results at relatively 2 low temperatures (T < Ta) to the retention of one-dimensional fiber morphology; although the fibers etching and formation of the trough-like longitudinal cavities and hillocks has been observed, see Fig. 2a and c. Some nanoneedles are created on the cavities edges of the eroded fibers. At elevated temperatures (T > Ta) for both CFC surfaces at fluences 1018-1019 ion/cm2 a crimped structure is created with the ribs of the crimps perpendicular to the fiber axis, see Fig. 2b and d. The crimping seems to be typical for the ion irradiation of carbon fibers. This feature was observed not only for the ion irradiation of composite materials, but also for separate carbon fibers [16]. Namely, the crimping was observed for 30 keV N+ irradiation of PAN fibers. It should be noted that irradiation in [7,8,16] was made by nitrogen ions which can form a C-N chemical compound. Argon ion bombardment used in the present study allow us to find that the cause of crimping is a pure physical ion-induced process. One may suppose that fiber crimping development might be the result of radiation-induced anisotropic dimensional changes (fiber radial swelling and axial shrinkage [1]) at the temperatures larger than Ta, when a fiber shell keeps its mosaic structure. The gradient of ion-induced radiation damage in surface layer also favors to crimp development. However, it has been observed that crimping formation disappears at fluences more than 1019 ion/cm2. The high fluence results in the loss of directional fiber anisotropy. The butt-ends of the fibers are transformed under ion irradiation into craters at all investigated temperatures due to collisional (physical) sputtering of the imperfect fiber kernel with a turbostratic structure, see Fig. 2e and f. A quantitative analysis of created topographical element microgeometry has been performed using laser goniophotometry (LGF) technique [14,15]. The distribution f(b) of local slope angle b of topographical element microfaces depends on both the ion fluence and irradiation temperature. A typical example of the distribution f(b) after irradiation at T < Ta for KUP-VM samples cut parallel to the fiber axis is presented in Fig. 3a. The initial (before irradiation) distribution f(b) in the laser beam incidence plane, which was parallel to a fiber axis, is narrow. As the target temperature under ion irradiation increases, the function f(b) broadens and at elevated temperatures (T > Ta) is transformed into a distribution with two near symmetrical maxima. After further sputtering (ut > 1019 ion/cm2) at T > Ta the fiber morphology structure dramatically breaks. The distributions f(b) for both along and across the carbon fibers become close to each other and correspond to a cosb-dependence. A typical example is

Please cite this article in press as: N.N. Andrianova et al., Erosion of carbon fiber composites under high-fluence heavy ion irradiation, Nucl. Instr. and Meth. B (2011), doi:10.1016/j.nimb.2010.12.063


N.N. Andrianova et al. / Nuclear Instruments and Methods in Physics Research B xxx (2011) xxx-xxx

3

Fig. 2. SEM and optical photographs of the KUP-VM (a and b) and Desna 4 (c-f) surface at room temperature (a, c, e) and T > 350 ÀC (b, d, f).

f ( ) , arb. un it
1,0

a
T=350 C
o

0,8

0,6

initial

0,4

0,2

T=20 C

o

0,0 -80

-60

-40

-20

, deg.

0

20

40

60

80

An analysis of measured Y(ut)-dependencies for 30 keV Ar+ irradiation of Desna 4 showed that at T < Ta irradiation with fluence ut $ 1 Ò 1019 ion/cm2 Y % 1 atoms/ion. It is close to Y for smooth graphite surface simulated by Eckstein using TRIM.SP (version trvmc 95) [17], see Fig. 4. As ut increases Y rises to the measured sputtering yields for KUP-VM, Y % 2.2 atoms/ion at ut > 3 Ò 1019 ion/cm2. The sputtering yield for these materials (KUP-VM and Desna 4) are close to those for polycrystalline graphites and glassy carbon [15]. The behavior of Y(ut)-dependence for Desna 4 obtained at T > Ta is different to that at T < Ta. At ut < 1 Ò 1019 ion/cm2 the sputtering yield is more than five times higher than Y at irradiation of Desna 4 at T < Ta. When ut increases to 2.5 Ò 1019 ion/cm2 the sputtering yield increases (Y % 7 atoms/ion) too. It is due to crimp formation and to the increase in the yield of oblique local ion incidence angles. With increasing ion fluence the sputtering yield approximately halves. Microscopy analysis shows that the reason of such behavior is due to changes in Desna 4 surface. Namely, the

f( ), arb.unit

b
along fiber cos

Y, at./ion

30 keV Ar

+

7 6 5 Desna 4 T = 400 C
across fiber
0

4 KUP-VM T ~ 70 C 3 2 Desna 4 T ~ 70 C
20 40 60
0 o

TRIM.SP

sphere cylinder plane

T=400 C
-60 -40 -20

o

, deg.

0

1 0 0 1 2
t, 10

Fig. 3. The distributions f(b) of local slope angles b at RT and T = 350 ÀC for KUP-VM cut out parallel to the fibers (a) and for Desna 4 at T = 400 ÀC and ut $ 4 Ò 1019 ion/ cm2 (b).

3
19

4 2 ion/cm

5

6

presented in Fig. 3b for CFC Desna 4. This ion-induced morphology we call the globe-like structure.

Fig. 4. The fluence dependences of measured sputtering yield Y and calculated ones for cylinder-like and sphere-like surface topography takes into account angular dependence of sputtering yield for smooth graphite surface (simulated by TRIM.SP [17]).

Please cite this article in press as: N.N. Andrianova et al., Erosion of carbon fiber composites under high-fluence heavy ion irradiation, Nucl. Instr. and Meth. B (2011), doi:10.1016/j.nimb.2010.12.063


4

N.N. Andrianova et al. / Nuclear Instruments and Methods in Physics Research B xxx (2011) xxx-xxx

developed crimps with the ribs perpendicular to a fiber axis is transformed into a more isotropic globular structure, which can significantly change the local angle of incidence on the surface topographical elements. Using the observed ion-induced morphology evolution and angular dependence of sputtering yield Y(h) analytical estimates of sputtering yield for rough surface hYi were made for cylinderlike and sphere-like surfaces using the distributions of local angle of incidence w(h)

at temperatures T > Ta leads to a crimped structure with the ribs perpendicular to fiber axis. At ion fluences P3 Ò 1019 ion/cm2 at T > Ta the fiber morphology with the crimps is transformed to a more isotropic globular structure. As a result the sputtering yield for Desna 4 decreases more than twice and becomes close to one for KUP-VM, Desna 4, polycrystalline graphites and glassy carbons measured at room temperature. Acknowledgements

hY i Ì

Zp
0

=2

Y ?hîÑ w?hîdh:

? 1î
The authors are grateful to M.A. Timofeev for SEM analysis and V.S. Avilkina for LGF measurements. This work is supported by the Ministry of Education and Science of Russian Federation (Contract No. 02.740.11.0389). References
[1] Yu.S. Virgiløv, I.P. Kalyagina, Inorg. Mater. 40 (Suppl. 1) (2004) 33. [2] G. Carter, The physics and applications of ion beam erosion, J. Phys. D: Appl. Phys. 34 (2001) R1-R22. [3] W.L. Chan, E. Chason, J. Appl. Phys. 101 (2007) 121301. [4] J. Roth, E. Tsitrone, A. Loarte, Nucl. Instrum. Meth. B 258 (2007) 253. [5] L. Begrambekov, C. Brosset, J. Bucalossi, E. Delchambre, J.P. Gunn, C. Grisola, M. Lipa, T. Loarer, R. Mitteau, P. Moner-Garbet, et al., J. Nucl. Mater. 363-365 (2007) 1148. [6] L.S. Novikov, M.I. Panasyuk, E.N. Voronina, AIP Conf. Proc. 1087 (2009) 637. [7] N.N. Andrianova, A.M. Borisov, Yu.S. Virgil`ev, E.S. Mashkova, A.S. Nemov, E.A. Pitirimova, M.A. Timofeev, Rentgenovskie, Sinkhrotronnye i Neitronnye Issledovaniya, 5 (2008) 59. [8] N.N. Andrianova, A.M. Borisov, E.S. Mashkova, Yu.S. Virgiløv, Nucl. Instrum. Meth. Phys. Res. B 267 (2009) 2778. [9] G.J. Dienes, G.B. Vineyard, Radiation Effects in Solids, Interscience Publishers Inc., New York, 1957. p. 243. [10] T.D. Burchell, MRS Bull. 22 (4) (1997) 29. [11] A.M. Borisov, E.S. Mashkova, Nucl. Instrum. Meth. B 258 (2007) 109. [12] A.M. Borisov, Yu.S. Virgil'ev, E.S. Mashkova, Rentgenovskie, Sinkhrotronnye i Neitronnye Issledovaniya, 1 (2008) 58. [13] E.S. Mashkova, V.A. Molchanov, Medium-Energy Ion Reflection from Solids, North-Holland, Amsterdam, 1985. p. 444. [14] N.N. Andrianova, A.M. Borisov, E.S. Mashkova, A.S. Nemov, V.I. Shulga, Nucl. Instrum. Meth. Phys. Res. B 230 (1-4) (2005) 583. [15] N.N. Andrianova, A.M. Borisov, E.S. Mashkova, Rentgenovskie, Sinkhrotronnye i Neitronnye Issledovaniya, 4 (2009) 77. [16] M.V. Ivanov, N.V. Gavrilov, T.A. Belyh, E.A. Ligacheva, L.V. Galijeva, A.E. Ligachev, V.V. Sohoreva, Surf. Coat. Technol. 201 (2007) 8326-8328. [17] W. Eckstein, I.M. Fayazov, E.S. Mashkova, V.A. Molchanov, A.V. Sidorov, A.I. Tolmachev, Nucl. Instrum. Meth. Phys. Res. B 67 (1992) 523. [18] R. Behrish, W. Eckstein, Sputtering by Particle Bombardment. Experiments and Computer Calculations from Threshold to MeV Energies, Springer, Berlin, 2007. p. 508. [19] W. Eckstein, Computer Simulation of Ion-Solid Interactions, Springer Series in Material Science, Springer, Berlin, 1991. p. 321.

For cylinder-like surface w(h) $ cos h and for sphere-like w(h) $ sin(2h). The angular dependence of sputtering yield Y(h) was taken from [18]

c Ðf hp Y ?hî Ì Y ?0îÑ cos Ó h0 2 c hp : Ñ exp b 1 Ð 1 cos Ó h0 2

? 2î

The parameters in (2) were obtained by fitting the yields calculated using TRIM.SP [17,19]. For 30 keV Ar+ irradiation the sputtering yield at h = 0À Y(0) = 0.96, hÓ Ì 90 , f = 2.4175, b = 0.3179, 0 c = 0.9919 [18]. The results of estimation are plotted in Fig. 4. One can see that at fluences more than 2-3 Ò 1019 ion/cm2 at T < Ta CFC Desna 4 and KUP-VM are sputtered like a cylinder surface and at T > Ta Desna 4 is sputtered like a sphere (or globular) surface. This corresponds with the observed ion-induced CFC morphology evolution. 4. Conclusions The erosion of carbon fiber composites KUP-VM and Desna 4 surface layers under high fluence (1018-1020 ion/cm2) 30 keV Ar+ ion irradiation has been studied. Ion-induced erosion results in the changes of carbon fiber structure which depend on temperature and ion fluence. Monitoring of ion-induced structural changes using temperature dependences of ion-induced electron emission yield has been shown that for Desna 4 and KUP-VM at dynamic annealing temperature Ta % 170 ÀC the transition from disordering at T < Ta to recrystallization at the temperature higher than Ta takes place. The temperature Ta is close to one for polycrystalline graphites. At temperatures T < Ta the etching of the fibers results in a formation of trough-like longitudinal cavities and hillocks. Irradiation

Please cite this article in press as: N.N. Andrianova et al., Erosion of carbon fiber composites under high-fluence heavy ion irradiation, Nucl. Instr. and Meth. B (2011), doi:10.1016/j.nimb.2010.12.063