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Modification of tribological properties of iron films during joint implantation of carbon and zirconium ions
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GOtlTINGS ELSEVIER
Surfaceand CoatingsTechnology92 ( t 997) 190-196
Modification of tribological properties of iron thin films during joint implantation of carbon and zirconium ions V.V. U g l o v a, V.V. K h o d a s e v i c h a, T . M . L a p c h u k a, D . P . R u s a l s k y a'*, I.V. K a s k o b Belorussian State University, pr. F. Scariny 4, Minsk 220080, Belarus b Fraunhofer Society, Institute of Integrated Circuits, Erlangen, Germany Received 12 December 1996; accepted 2l March 1997
Abstract
The aim of the present work was to investigate the effect of zirconium and carbon implantation on iron films. Tribological properties, element and phase composition of iron thin-film samples during monoetement [C +, Zr+~Fe], subsequent [Zr+~(C+~Fe), C+~(Zr+~Fe)] and joint [(C + +Zr+)~Fe] implantation were investigated. © 1997 Published by Elsevier Science S.A. Keywords." Double ion implantation; Tribological properties
1. Introduction
Theoretical and experimental investigations have been carried out which have shown that multielement implantation of metal and metalloid ions is a possible way to improve surface mechanical properties [1-4]. A pulsed heavy ion source provides a powerful tool for the surface modification of materials (wear, corrosion and oxidation) for various applications [ 1,5]. The effect of ion beam pulsing is a topic of interest for studies of radiation effects and ion beam modification of materials. Significant differences in phase composition and phase stability have been found for slowly pulsed irradiation compared with those obtained in continuous implantation. The greatest change is apparent in the nature of precipitate formation [6,7]. The focus of this paper is the investigation of various combinations of C + + Zr + dual implantation into iron thin films for the modification of tribological properties. The surface composition, distribution profiles, new phase formation and complex carbon film formation in the implanted regions have also been studied. 2. Experimental Iron films of ~100 nm thickness were formed by sputter ion plating at a temperature of 250 °C on ceramic * Correspondingauthor. Tel.(7-0172) 26-58-34;
Fax: (7-0172) 26-59-40, 20-82-72;e-mail:[email protected]
substrates (90 wt.% SiOz, 10 wt.% species) and on freshly cleaved NaC1 in a vacuum of about 2.10 -3 Pa. The rate of deposition was 0.5 nm s -1. The irradiation by Zr and C ions was conducted by monoelement (MII) [C +, Zr+~Fe], subsequent (SII) [Zr+~(C+-~Fe), C+--,(Zr+~Fe)] and joint (JII) [(C + + Z r + ) ~ F e ] ion implantation with low energies from 5 to 16 keV in the dose range 10~6-1018 ions cm -2 at room temperature. The irradiation regimes are presented in Table 1. The treatment of iron layers was carried out on a SVETLJACHOK implanter, a schematic diagram of which is presented in Fig. 1. This implanter uses two vacuum arc repetitively pulsed (v_<0-50 Hz) ion sources capable of implanting any kind of metal ions and some metalloid ions [5,7,8]. No mass separation of the ion beam was used for the implantation. The pressure in the target chamber was 2" 10- 3 Pa. Tribologicat tests were carried out with TAYt device. The scheme of the test is presented in Fig. 2. The type of tribological test was "sphere-on-plane", dry sliding dynamic friction, without lubrication. The line sample velocity was 0.4cm s -1. Diamond was used as an indenter. The curvature radius of the sliding surface of the indenter was t mm. The load on the indenter was 0.6N. The phase composition of the films before and after implantation was investigated by transmission electron diffraction (TED) analysis. The surface composition and distribution profiles of the implanted zirconium, carbon
0257-8972/97/$17.00 © 1997Publishedby ElsevierScienceS.A.All rights reserved. PII S0257-8972 (97) 00106-0
V.V. Uglov et al. / Surface and Coatings Technology 92 (1997) 190±196
191
Table I Implantation regimes N
Implantation ions
Ion-beam treatment regimes
C+
MII
E(keV)
j(F.A cm -2)
D(ions cm -2 )
E(keV)
j ( g A cm -2 )
D(ions cm -2)
5
5
I0 i6 4 ' 10 i6 8' 10 i6 16" 1016 8" 10 i6 16" 1016 16' I016 8' 10 i6 i 6 ' 10 i6 14' 10 i6 28" 1016 56' 1016 84" 1016
16
4
1016
C ÷~Fe Zr + --+Fe 2.
SII Zr ÷ --,(C + --,Fe)
5
5
12
5
C + ~ ( Z r + --*Fe) JII
(C + + Z r +)-+Fe
16
4
i2
2
7' 10 i6 14" i016 7" 1016 1016 14' 10 i6 7" iO I6 I 4 ' 10 i6 6' 1016 12" i0 i6 24" 10 I6 36' 10 i6
E
•
>o
/
I
÷
o
3zv
......
meE ZN~aeY (z-30) kV
VACUUM CIIAMBER
PIYM2 Fig. I. Schematic diagram of the S V E T L J A C H O K implanter.
( .
~
3. Resultsanddiscussion
r~
/.tl I
"-~o~ S
..........i.........../ liil/i';.~.............. A
M
P
L
E
Fig. 2. Scheme of friction test with TAY1 tribometer.
and other elements (e.g. oxygen and iron) were determined using Rutherford backscattering spectroscopy
3.1.
Tribological tests
The variation in the sample friction coefficient as a function of the indenter sliding distance for different implantation doses and irradiation conditions (MII, SII, JII) is given in Figs. 3-7. For all implantation variants a decrease in the friction coefficient was observed. For JII and SII the friction coefficient was 1.5-2.4 times less than for an unimplanted sample. The wear lifetime of C ÷ ~ (Zr + --+Fe) and (C + + Zr ÷) ~ F e was greater than
that of unimplanted samples, However, it should be
V. K Ugtov et al. / Smfaee and Coatings Technology 92 (1997) 190-196
192
0.040
0.040
o
~
o
o
<~/~/.:
0.035
a
o
o
. . . . . . . . .
~
. . . . . . . . . . . . . .
¢)
-d
'5
~
!
1.~01s C t - > Fe 4."016 0" -> fe 8."0~ C+~ +-> .6~10 C - > Fe
o
7
-
un
mD
7.10
~6a nZrt e d -> +
1.4,1~'" z~" - ,
,
Fe
0.030
1 . 1 0 " Zr*
0.020
......
l .
.
.
. . 0.50
. ~.50
1.00 sliding
distcnce,
2
u
0,020
4.00
......... 0.00
~ . . . .
0,035
o
. . . . . . . . .
i= ,
i
i
]
. . . . . . . . .
t .00
]
1,50
distance,
4.00
m
Fig. 6. Friction coefficient vs sliding distance for iron films subsequently implanted with carbon and zirconium,
~ ' ~
o
~
sliding
0045 o
u o
0.50
m
0.040
e
Fe)
"1
Fig. 3. Friction coefficient vs sliding distance for iron films implanted with carbon.
J
C+ +
3
+~ 0.025
:: ......
O.O0
+
(1.6. t0--
O
0
:
->
15
C + Fe) (1.6,1,0 '~ c* + re)
(8.10
"~ o~o3o
.o *~ 0,025
. . . . . . . . .
0.035
q)
unimp~cnted
o
f
\
1 ~
\
~_
. . . . . . . . .
1 2 -
unimpJa_nLed 1 4~ 0 ~ C ÷ +
3 -
28.10
- 1-1~ -r* 5~" U Z 1 ' 2 u 17 zr ~' 4 - 5:6,~0'; < + 2.4.10 z~ --~]~/ C +1 3"6"1017 zr÷ ~7 C*
(D
..... o . . . . . . . . .
'5 0.035 L~ q~
O © C O
0.030
4 -
"-~ 0 . 0 2 5
0,020
1 2 5 4 ~
o.oo
i
0.50
r
,,,
i .....
l.oo
sliding
0 .[unimp~anted !.10' Zr * - > % 7 . 1 0 :~ Z r + - > Fe 1 . 4 . 1 0 ~ T Z r + - > Fe ", , , ,
i
1.5o
distarce,
0,015
unimNanted 8.~0'6170 + +-->. ( 7 . 1 0 ' ! ZfT" ~- + ) 1,6.10 C -> (1,4.10 Zr+
~ / ~
Fe)
2 ......... m
©
0.020
0,015
fl . . . . . . . . . O.O0
~ ....
r ....
0.50
~,,
,,i,,,~
1.00
slid;ng
distcnce,
sliding
distance,
,,,I
1.50
3.00
m
Fig. 7. Friction coefficient vs sliding distance for iron films jointly implanted with carbon and zirconium.
noted that for the samples shnuttaneously irradiated by carbon and zirconium with doses more than 5.6.10 ~7 C ÷ cm -2 and 2.4.1017 Zr + cm -2 there was a sharp increase in friction coefficient followed by a decrease. The peak widened as the implantation dose increased. With further increase in the sliding distance the friction coefficient became less than that of the initial sample. The decrease in the surface friction coefficient and the improvement of wear lifetime resulted from the creation of a thin complex carbon film and an alloying layer under a carbon layer. This was confirmed by RBS and TED measurements for Zr + + C + subsequent and joint ion implantation.
0.035 -
1,00
rn
1
3
0.50
4.00
0,040
X 2
~ , . , , ~ , , , I'r=~r~--r ~ , , , L , . . . . .
0.00
'
Fig. 4. Friction coefficient vs sliding distance for iron films implanted with zirconium.
q~ '~ 0.030 LU_ -@ 0 0.025 C 0
2
:~ 0.025
...... 1.50
4.00
rn
Fig. 5. Friction coefficient vs sliding distance for iron films subsequently impIanted with zirconium and carbon.
3.2. TED analysis The electron diffraction patterns of the films taken before and after bombardment are shown in Figs. 8a
V. V. Uglovetal. / Smface and Coatings Technology 92 (]997) 190-196 ~m
100
64 e7 06
193
,
2
c~-:Pe
a
70 SS
~? 75 ©
27
.9~c ~._,.~o5o-_ 25-
4
0
t
0
x-~e=O
b
~,
,i
10
t i
20
~d,
50
depth, nm
40
50
60
Fig. 9. Concentration profiles of (1) C, (2) Fe, (3) O, and (4) Zr x 10 in the 1.4.101~ Zr + cm -2 implanted iron film.
,.eros 0,2027
ZrO ~-~e
Fig. 8. Electron diffraction patterns of (a) the original and (b) (5.6' 10 ~v C + c m - 2 + 2 . 4 • 10 ~7 Zr + cm -2) jointly implanted iron films.
and b, respectively. Electron microscopy investigations showed that JII induced carbide phase formation in thin surface layers. The TED patterns of Z r + + C ÷ jointimplanted iron thin films indicated that z-Fe2C and ZrC were formed in an implanted layer.
3.3. RBS analysis The zirconium, carbon, oxygen and iron depth distributions for MII (1.4.101~ Zr ÷ cm-2-+Fe) and various regimes of SII are shown in Figs. 9 and 10, respectively. Figs. 11 and 12 show the evolution of the backscattering spectra (Fig. 11) and concentration profiles of the implanted Zr and C ions (Fig. 12) for various doses of carbon and zirconium JII. It should be noted that the quantities of incorporated zirconium were less than indicated doses. It may be connected with this that the zirconium ion beam contains not only zirconium but also other ions (carbon), and this requires additional investigation. The carbon and zirconium distribution profiles were very different for samples after SII and JII. RBS measurements for SII [Zr+~(C+--+Fe), C+--+(Zr+--+Fe)] and JII [(C++Zr+)-+Fe] indicated that there were thin carbon films on the surface. It is known that carbon is present in the implantation cham-
surface is doped in addition with carbon by recoil implantation of adsorbed carbon residual gas molecules. This recoil implantation in the case of SII and JII is very effective because the transferred energy is high. Additional implantation of the carbon ions is possible by means of gas separation from the cathode surface (ion injector) at the arc discharge plasma. The layer of carbon ("sacrificial layer" [10]) effectively prevents sputtering (Szr-ve----14 atoms/ion) of iron. It is obvious from Fig. 11 that the iron film peak width was practically constant for all ion implantation doses. During zirconium and carbon JII the thickness of the surface carbon film continued to increase with the increase in dose. In accordance with RBS results, the depth migration of carbon after SII for the combination of ions Zr+--+(C+~Fe) was less than after C + ~ ( Z r + ~ F e ) . There is an extended tail in the C depth profile in Fig. 10a, which is matched by a plateau in the Fe distribution. This is indirect confirmation of the formation of Fe-C bonds here. There is no such a tail in Fig. 10b. This may be explained by the effect of radiation-induced diffusion. According to TRIM calculation, zirconium ion creates 344 vacancies in iron and carbon ion creates 76 vacancies. When a carbon ion penetrates into the surface layer which is saturated by vacancies after preliminary zirconium irradiation, the formation of vacancy-carbon atom complexes is possible. These complexes are mobile and may diffuse deep into the sample. The shape of the zirconium distribution is Gaussian-like for the low doses of JII up to 1.2" 1017 Zr ÷ cm -2. The distributions corresponding to 2.4' 1017Zr ÷ cm -2 and above show two components, which are better separated for high implantation doses. The first peak is located in the carbon layer and the second peak is just below the surface. The first component, located at a depth of 220 A, has a maximum
K K Uglov et al. / Surface and Coatings Technology 92 (1997) 190-196
I94
1O0 t ~
1
~
1
2
1O0 •
<]
2
75
4:¢10 Zr + 1.4'1017 Zr~->'(1.6.10'7 C+ + Fe •
/,,.~
200
17
+
17
+
Fe
B-
4-00
600
800
/I/000
8
/
O O
0
r 0
200
400
600
800
S
A
1000
depth, ongstrom Fig. 10. Concentration profiles of (1) C, (2) Fe, and (3) Zr x 10 for iron films subsequently implanted with zirconium and carbon.
80o02
g 8
~B
I
- uoim tQOtod
28.!0-- C~ + ' 2.10 17~7 Z r * 5.6.~1017 C÷ + 2.4.10 Zr÷ Zr+
-6
200
700
1200
1700
energy, keV Fig. 11. Rutherford backscattering spectra for iron films jointiy implanted with zirconium and carbon.
zirconium concentration of about 3.1 at.%, while the second shows a maximum concentration above 4.8 at.% at 420A (Fig. 12b). Such complex zirconium profiles may be explained in two ways. First, the shift of the zirconium profile into the surface carbon layer occurs during the implantation process as a result of the movement of the surface carbon film. Second, a noncharge-analysed ion beam is used for the irradiation of the samples and it is known that the zirconium ion beam contains multicharged ions [11,12]. Such a complex zirconium profile is obtained through the combination of these two reasons. The maximum in the friction coefficient of the samples after JII (Fig. 7) is definitely explained by the double
peaked layer of zirconium. The first zirconium peak lay in a surface carbon layer (Fig. 12). According to the TED results, zirconium in the sample was present as a carbide ZrC (Fig. 8). This carbide had high hardness, HV~-3000 kg mm -2, and therefore during the indenter motion on a surface carbon layer it played the role of an abrasive, thus increasing the friction coefficient. The second zirconium peak lay in the iron and, apparently, zirconium was in a solid solution here, thus increasing the matrix hardness. As a result of this, when the indenter reached the surface of an iron film the friction coefficient decreased sharply. The best results with the friction after JII were obtained for the irradiation doses 2.9" 10~7C + cm -2 and 1.2-10~TZr + cm -2. In this case
H V. Uglov etal. / Swface and Coatings Technology 92 (1997) 190-196
195
/~ A:' 2.8,10~7C++ 1.2.~10'7Zr + ' ,~ 7 +
o
2oo
Z
400: soo see depth, ongstrorn
~ooo
Fig. 12. Concentration profiles of (1) C, (2) Fe, and (3) Zr x 10 for iron films jointly implanted with zirconium and carbon.
zirconium lay in iron near the dividing boundary between an iron film and a superficial carbon layer (Fig. 12a). During indenter friction measurements on such a system, sliding on a iron film strengthened by zirconium occurs and surface carbon plays the part of a solid lubricant.
(3) The investigation of the phase composition of the implanted films by TED showed that carbide transformation, which causes the formation of X-Fe2C carbide and ZrC carbide on the basis of implanted elements, occurred in films during implantation of zirconium and carbon.
4. Conclusions Some important results are summarized as follows. (1) Implantation of Zr +, C+, Zr + + C + improved the surface mechanical properties of iron thin-film samples. Zirconium and carbon implantation (SII and JII regimes) reduced the friction coefficient of iron films. The largest friction coefficient decrease at the beginning and at steady-state wear was 2.4 and 1.7 times, respectively. The changes were observed in the implantation systems: 1.6.1017 C + cm-2-+(1.4 • 1017 Zr + c m - 2 ~ F e ) and (2.8.1017 C + c m - 2 + 1.2 • 1017 Zr + cm-2)---,Fe. (2) Zirconium depth distributions corresponding to JII (5.6" l017 C + cm-2+2.4 • 1017 Zr + cm -2) and more showed two components, which were better separated for high implantation doses. The presence of impurity elements (in particular carbon contamination) during the implantation process led to the formation of surface carbon films. This layer of carbon (sacrificial layer) effectively prevented sputtering (Szr-v, ~ 14 atoms/ion) of iron. During zirconium and carbon JII the thickness of a surface carbon film continued to increase with increasing dose.
Acknowledgement This work was supported by the Fund of Fundamental Investigations of Belarus Republic (Grant No. 95-231), International Atomic Energy Agency (Research Contract No. 9011) and International Soros Science Education Program.
:References [1] G.S. Was, L.E. Retm, D. FoIIstaedt, Phase Formation and Modification by Beam-Solid Interactions, MRS, Boston, 1992, p. 683. [2] V.V. Uglov, A.K. Kuleshov, Vac. Tech. Technol. 2 (1991) 24. [3] J.I. Ofiate, F. Alonso, J.L. Viviente, A. Arizaga, Surf. Coat. Technoi. 65 (1994) I65. [4] T. Zhang, H. Huang, C. Ji, J. Chen, G. Sun, H. Zhang, X. Zhang, Surf. Coat. Tectmol. 65 (1994) 148. [5] A.M. Mazurkevich, V.V. Khodasevich, V.V. Uglov, V.A. Kutsanov, A.G. Serov, V.V. Pankratov, A.G. Kobyak, V.V. Bobkov, Vac. Tech. Technol. 1 (i991) 18. [6] E.M. Lee, N.H. Packan, M.B. Lewis, L.K. Mausur, Nucl. Instrum. Methods B6 (1986) 251.
196
V.V. Ugtov et at. / Surface and Coatings Technology 92 (1997) 190-196
[7] V.V. Uglov, V.V. Khodasevich, D.P. Rusalsky, I.V. Kasko, in: Proceedings of the Third Conference on Modification of Constr. Material Properties by Charged Particle Beams, voL 2, ISE SO RAN, Tomsk, 1994, p. 38. [8] V.V. Uglov, V.V. Khodasevich, N.N. Cherenda, I.V. Kasko, V.A. Kutsanov, Surf. Coat. TechnoL 66 (1994) 283.
[9] M.A. E1 Khakani, H. Jaffrezic, G. Marest, N. Moneoffre, J. Tousset, NucI. Instrum. Methods B59/60 (1991) 751. [10] L. Claphan, Surf. Coat. Technol. 65 (1994) 24. [11] I.G. Brown, The Physics and Technology of Ion Sources, WileyInterscience, New York, 1989, p. 567. [12] I,G. Brown, W. Feinberg, J.E. Galvin, J. Appi. Phys. I0 (1988)4889.
GOtlTINGS ELSEVIER
Surfaceand CoatingsTechnology92 ( t 997) 190-196
Modification of tribological properties of iron thin films during joint implantation of carbon and zirconium ions V.V. U g l o v a, V.V. K h o d a s e v i c h a, T . M . L a p c h u k a, D . P . R u s a l s k y a'*, I.V. K a s k o b Belorussian State University, pr. F. Scariny 4, Minsk 220080, Belarus b Fraunhofer Society, Institute of Integrated Circuits, Erlangen, Germany Received 12 December 1996; accepted 2l March 1997
Abstract
The aim of the present work was to investigate the effect of zirconium and carbon implantation on iron films. Tribological properties, element and phase composition of iron thin-film samples during monoetement [C +, Zr+~Fe], subsequent [Zr+~(C+~Fe), C+~(Zr+~Fe)] and joint [(C + +Zr+)~Fe] implantation were investigated. © 1997 Published by Elsevier Science S.A. Keywords." Double ion implantation; Tribological properties
1. Introduction
Theoretical and experimental investigations have been carried out which have shown that multielement implantation of metal and metalloid ions is a possible way to improve surface mechanical properties [1-4]. A pulsed heavy ion source provides a powerful tool for the surface modification of materials (wear, corrosion and oxidation) for various applications [ 1,5]. The effect of ion beam pulsing is a topic of interest for studies of radiation effects and ion beam modification of materials. Significant differences in phase composition and phase stability have been found for slowly pulsed irradiation compared with those obtained in continuous implantation. The greatest change is apparent in the nature of precipitate formation [6,7]. The focus of this paper is the investigation of various combinations of C + + Zr + dual implantation into iron thin films for the modification of tribological properties. The surface composition, distribution profiles, new phase formation and complex carbon film formation in the implanted regions have also been studied. 2. Experimental Iron films of ~100 nm thickness were formed by sputter ion plating at a temperature of 250 °C on ceramic * Correspondingauthor. Tel.(7-0172) 26-58-34;
Fax: (7-0172) 26-59-40, 20-82-72;e-mail:[email protected]
substrates (90 wt.% SiOz, 10 wt.% species) and on freshly cleaved NaC1 in a vacuum of about 2.10 -3 Pa. The rate of deposition was 0.5 nm s -1. The irradiation by Zr and C ions was conducted by monoelement (MII) [C +, Zr+~Fe], subsequent (SII) [Zr+~(C+-~Fe), C+--,(Zr+~Fe)] and joint (JII) [(C + + Z r + ) ~ F e ] ion implantation with low energies from 5 to 16 keV in the dose range 10~6-1018 ions cm -2 at room temperature. The irradiation regimes are presented in Table 1. The treatment of iron layers was carried out on a SVETLJACHOK implanter, a schematic diagram of which is presented in Fig. 1. This implanter uses two vacuum arc repetitively pulsed (v_<0-50 Hz) ion sources capable of implanting any kind of metal ions and some metalloid ions [5,7,8]. No mass separation of the ion beam was used for the implantation. The pressure in the target chamber was 2" 10- 3 Pa. Tribologicat tests were carried out with TAYt device. The scheme of the test is presented in Fig. 2. The type of tribological test was "sphere-on-plane", dry sliding dynamic friction, without lubrication. The line sample velocity was 0.4cm s -1. Diamond was used as an indenter. The curvature radius of the sliding surface of the indenter was t mm. The load on the indenter was 0.6N. The phase composition of the films before and after implantation was investigated by transmission electron diffraction (TED) analysis. The surface composition and distribution profiles of the implanted zirconium, carbon
0257-8972/97/$17.00 © 1997Publishedby ElsevierScienceS.A.All rights reserved. PII S0257-8972 (97) 00106-0
V.V. Uglov et al. / Surface and Coatings Technology 92 (1997) 190±196
191
Table I Implantation regimes N
Implantation ions
Ion-beam treatment regimes
C+
MII
E(keV)
j(F.A cm -2)
D(ions cm -2 )
E(keV)
j ( g A cm -2 )
D(ions cm -2)
5
5
I0 i6 4 ' 10 i6 8' 10 i6 16" 1016 8" 10 i6 16" 1016 16' I016 8' 10 i6 i 6 ' 10 i6 14' 10 i6 28" 1016 56' 1016 84" 1016
16
4
1016
C ÷~Fe Zr + --+Fe 2.
SII Zr ÷ --,(C + --,Fe)
5
5
12
5
C + ~ ( Z r + --*Fe) JII
(C + + Z r +)-+Fe
16
4
i2
2
7' 10 i6 14" i016 7" 1016 1016 14' 10 i6 7" iO I6 I 4 ' 10 i6 6' 1016 12" i0 i6 24" 10 I6 36' 10 i6
E
•
>o
/
I
÷
o
3zv
......
meE ZN~aeY (z-30) kV
VACUUM CIIAMBER
PIYM2 Fig. I. Schematic diagram of the S V E T L J A C H O K implanter.
( .
~
3. Resultsanddiscussion
r~
/.tl I
"-~o~ S
..........i.........../ liil/i';.~.............. A
M
P
L
E
Fig. 2. Scheme of friction test with TAY1 tribometer.
and other elements (e.g. oxygen and iron) were determined using Rutherford backscattering spectroscopy
3.1.
Tribological tests
The variation in the sample friction coefficient as a function of the indenter sliding distance for different implantation doses and irradiation conditions (MII, SII, JII) is given in Figs. 3-7. For all implantation variants a decrease in the friction coefficient was observed. For JII and SII the friction coefficient was 1.5-2.4 times less than for an unimplanted sample. The wear lifetime of C ÷ ~ (Zr + --+Fe) and (C + + Zr ÷) ~ F e was greater than
that of unimplanted samples, However, it should be
V. K Ugtov et al. / Smfaee and Coatings Technology 92 (1997) 190-196
192
0.040
0.040
o
~
o
o
<~/~/.:
0.035
a
o
o
. . . . . . . . .
~
. . . . . . . . . . . . . .
¢)
-d
'5
~
!
1.~01s C t - > Fe 4."016 0" -> fe 8."0~ C+~ +-> .6~10 C - > Fe
o
7
-
un
mD
7.10
~6a nZrt e d -> +
1.4,1~'" z~" - ,
,
Fe
0.030
1 . 1 0 " Zr*
0.020
......
l .
.
.
. . 0.50
. ~.50
1.00 sliding
distcnce,
2
u
0,020
4.00
......... 0.00
~ . . . .
0,035
o
. . . . . . . . .
i= ,
i
i
]
. . . . . . . . .
t .00
]
1,50
distance,
4.00
m
Fig. 6. Friction coefficient vs sliding distance for iron films subsequently implanted with carbon and zirconium,
~ ' ~
o
~
sliding
0045 o
u o
0.50
m
0.040
e
Fe)
"1
Fig. 3. Friction coefficient vs sliding distance for iron films implanted with carbon.
J
C+ +
3
+~ 0.025
:: ......
O.O0
+
(1.6. t0--
O
0
:
->
15
C + Fe) (1.6,1,0 '~ c* + re)
(8.10
"~ o~o3o
.o *~ 0,025
. . . . . . . . .
0.035
q)
unimp~cnted
o
f
\
1 ~
\
~_
. . . . . . . . .
1 2 -
unimpJa_nLed 1 4~ 0 ~ C ÷ +
3 -
28.10
- 1-1~ -r* 5~" U Z 1 ' 2 u 17 zr ~' 4 - 5:6,~0'; < + 2.4.10 z~ --~]~/ C +1 3"6"1017 zr÷ ~7 C*
(D
..... o . . . . . . . . .
'5 0.035 L~ q~
O © C O
0.030
4 -
"-~ 0 . 0 2 5
0,020
1 2 5 4 ~
o.oo
i
0.50
r
,,,
i .....
l.oo
sliding
0 .[unimp~anted !.10' Zr * - > % 7 . 1 0 :~ Z r + - > Fe 1 . 4 . 1 0 ~ T Z r + - > Fe ", , , ,
i
1.5o
distarce,
0,015
unimNanted 8.~0'6170 + +-->. ( 7 . 1 0 ' ! ZfT" ~- + ) 1,6.10 C -> (1,4.10 Zr+
~ / ~
Fe)
2 ......... m
©
0.020
0,015
fl . . . . . . . . . O.O0
~ ....
r ....
0.50
~,,
,,i,,,~
1.00
slid;ng
distcnce,
sliding
distance,
,,,I
1.50
3.00
m
Fig. 7. Friction coefficient vs sliding distance for iron films jointly implanted with carbon and zirconium.
noted that for the samples shnuttaneously irradiated by carbon and zirconium with doses more than 5.6.10 ~7 C ÷ cm -2 and 2.4.1017 Zr + cm -2 there was a sharp increase in friction coefficient followed by a decrease. The peak widened as the implantation dose increased. With further increase in the sliding distance the friction coefficient became less than that of the initial sample. The decrease in the surface friction coefficient and the improvement of wear lifetime resulted from the creation of a thin complex carbon film and an alloying layer under a carbon layer. This was confirmed by RBS and TED measurements for Zr + + C + subsequent and joint ion implantation.
0.035 -
1,00
rn
1
3
0.50
4.00
0,040
X 2
~ , . , , ~ , , , I'r=~r~--r ~ , , , L , . . . . .
0.00
'
Fig. 4. Friction coefficient vs sliding distance for iron films implanted with zirconium.
q~ '~ 0.030 LU_ -@ 0 0.025 C 0
2
:~ 0.025
...... 1.50
4.00
rn
Fig. 5. Friction coefficient vs sliding distance for iron films subsequently impIanted with zirconium and carbon.
3.2. TED analysis The electron diffraction patterns of the films taken before and after bombardment are shown in Figs. 8a
V. V. Uglovetal. / Smface and Coatings Technology 92 (]997) 190-196 ~m
100
64 e7 06
193
,
2
c~-:Pe
a
70 SS
~? 75 ©
27
.9~c ~._,.~o5o-_ 25-
4
0
t
0
x-~e=O
b
~,
,i
10
t i
20
~d,
50
depth, nm
40
50
60
Fig. 9. Concentration profiles of (1) C, (2) Fe, (3) O, and (4) Zr x 10 in the 1.4.101~ Zr + cm -2 implanted iron film.
,.eros 0,2027
ZrO ~-~e
Fig. 8. Electron diffraction patterns of (a) the original and (b) (5.6' 10 ~v C + c m - 2 + 2 . 4 • 10 ~7 Zr + cm -2) jointly implanted iron films.
and b, respectively. Electron microscopy investigations showed that JII induced carbide phase formation in thin surface layers. The TED patterns of Z r + + C ÷ jointimplanted iron thin films indicated that z-Fe2C and ZrC were formed in an implanted layer.
3.3. RBS analysis The zirconium, carbon, oxygen and iron depth distributions for MII (1.4.101~ Zr ÷ cm-2-+Fe) and various regimes of SII are shown in Figs. 9 and 10, respectively. Figs. 11 and 12 show the evolution of the backscattering spectra (Fig. 11) and concentration profiles of the implanted Zr and C ions (Fig. 12) for various doses of carbon and zirconium JII. It should be noted that the quantities of incorporated zirconium were less than indicated doses. It may be connected with this that the zirconium ion beam contains not only zirconium but also other ions (carbon), and this requires additional investigation. The carbon and zirconium distribution profiles were very different for samples after SII and JII. RBS measurements for SII [Zr+~(C+--+Fe), C+--+(Zr+--+Fe)] and JII [(C++Zr+)-+Fe] indicated that there were thin carbon films on the surface. It is known that carbon is present in the implantation cham-
surface is doped in addition with carbon by recoil implantation of adsorbed carbon residual gas molecules. This recoil implantation in the case of SII and JII is very effective because the transferred energy is high. Additional implantation of the carbon ions is possible by means of gas separation from the cathode surface (ion injector) at the arc discharge plasma. The layer of carbon ("sacrificial layer" [10]) effectively prevents sputtering (Szr-ve----14 atoms/ion) of iron. It is obvious from Fig. 11 that the iron film peak width was practically constant for all ion implantation doses. During zirconium and carbon JII the thickness of the surface carbon film continued to increase with the increase in dose. In accordance with RBS results, the depth migration of carbon after SII for the combination of ions Zr+--+(C+~Fe) was less than after C + ~ ( Z r + ~ F e ) . There is an extended tail in the C depth profile in Fig. 10a, which is matched by a plateau in the Fe distribution. This is indirect confirmation of the formation of Fe-C bonds here. There is no such a tail in Fig. 10b. This may be explained by the effect of radiation-induced diffusion. According to TRIM calculation, zirconium ion creates 344 vacancies in iron and carbon ion creates 76 vacancies. When a carbon ion penetrates into the surface layer which is saturated by vacancies after preliminary zirconium irradiation, the formation of vacancy-carbon atom complexes is possible. These complexes are mobile and may diffuse deep into the sample. The shape of the zirconium distribution is Gaussian-like for the low doses of JII up to 1.2" 1017 Zr ÷ cm -2. The distributions corresponding to 2.4' 1017Zr ÷ cm -2 and above show two components, which are better separated for high implantation doses. The first peak is located in the carbon layer and the second peak is just below the surface. The first component, located at a depth of 220 A, has a maximum
K K Uglov et al. / Surface and Coatings Technology 92 (1997) 190-196
I94
1O0 t ~
1
~
1
2
1O0 •
<]
2
75
4:¢10 Zr + 1.4'1017 Zr~->'(1.6.10'7 C+ + Fe •
/,,.~
200
17
+
17
+
Fe
B-
4-00
600
800
/I/000
8
/
O O
0
r 0
200
400
600
800
S
A
1000
depth, ongstrom Fig. 10. Concentration profiles of (1) C, (2) Fe, and (3) Zr x 10 for iron films subsequently implanted with zirconium and carbon.
80o02
g 8
~B
I
- uoim tQOtod
28.!0-- C~ + ' 2.10 17~7 Z r * 5.6.~1017 C÷ + 2.4.10 Zr÷ Zr+
-6
200
700
1200
1700
energy, keV Fig. 11. Rutherford backscattering spectra for iron films jointiy implanted with zirconium and carbon.
zirconium concentration of about 3.1 at.%, while the second shows a maximum concentration above 4.8 at.% at 420A (Fig. 12b). Such complex zirconium profiles may be explained in two ways. First, the shift of the zirconium profile into the surface carbon layer occurs during the implantation process as a result of the movement of the surface carbon film. Second, a noncharge-analysed ion beam is used for the irradiation of the samples and it is known that the zirconium ion beam contains multicharged ions [11,12]. Such a complex zirconium profile is obtained through the combination of these two reasons. The maximum in the friction coefficient of the samples after JII (Fig. 7) is definitely explained by the double
peaked layer of zirconium. The first zirconium peak lay in a surface carbon layer (Fig. 12). According to the TED results, zirconium in the sample was present as a carbide ZrC (Fig. 8). This carbide had high hardness, HV~-3000 kg mm -2, and therefore during the indenter motion on a surface carbon layer it played the role of an abrasive, thus increasing the friction coefficient. The second zirconium peak lay in the iron and, apparently, zirconium was in a solid solution here, thus increasing the matrix hardness. As a result of this, when the indenter reached the surface of an iron film the friction coefficient decreased sharply. The best results with the friction after JII were obtained for the irradiation doses 2.9" 10~7C + cm -2 and 1.2-10~TZr + cm -2. In this case
H V. Uglov etal. / Swface and Coatings Technology 92 (1997) 190-196
195
/~ A:' 2.8,10~7C++ 1.2.~10'7Zr + ' ,~ 7 +
o
2oo
Z
400: soo see depth, ongstrorn
~ooo
Fig. 12. Concentration profiles of (1) C, (2) Fe, and (3) Zr x 10 for iron films jointly implanted with zirconium and carbon.
zirconium lay in iron near the dividing boundary between an iron film and a superficial carbon layer (Fig. 12a). During indenter friction measurements on such a system, sliding on a iron film strengthened by zirconium occurs and surface carbon plays the part of a solid lubricant.
(3) The investigation of the phase composition of the implanted films by TED showed that carbide transformation, which causes the formation of X-Fe2C carbide and ZrC carbide on the basis of implanted elements, occurred in films during implantation of zirconium and carbon.
4. Conclusions Some important results are summarized as follows. (1) Implantation of Zr +, C+, Zr + + C + improved the surface mechanical properties of iron thin-film samples. Zirconium and carbon implantation (SII and JII regimes) reduced the friction coefficient of iron films. The largest friction coefficient decrease at the beginning and at steady-state wear was 2.4 and 1.7 times, respectively. The changes were observed in the implantation systems: 1.6.1017 C + cm-2-+(1.4 • 1017 Zr + c m - 2 ~ F e ) and (2.8.1017 C + c m - 2 + 1.2 • 1017 Zr + cm-2)---,Fe. (2) Zirconium depth distributions corresponding to JII (5.6" l017 C + cm-2+2.4 • 1017 Zr + cm -2) and more showed two components, which were better separated for high implantation doses. The presence of impurity elements (in particular carbon contamination) during the implantation process led to the formation of surface carbon films. This layer of carbon (sacrificial layer) effectively prevented sputtering (Szr-v, ~ 14 atoms/ion) of iron. During zirconium and carbon JII the thickness of a surface carbon film continued to increase with increasing dose.
Acknowledgement This work was supported by the Fund of Fundamental Investigations of Belarus Republic (Grant No. 95-231), International Atomic Energy Agency (Research Contract No. 9011) and International Soros Science Education Program.
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V.V. Ugtov et at. / Surface and Coatings Technology 92 (1997) 190-196
[7] V.V. Uglov, V.V. Khodasevich, D.P. Rusalsky, I.V. Kasko, in: Proceedings of the Third Conference on Modification of Constr. Material Properties by Charged Particle Beams, voL 2, ISE SO RAN, Tomsk, 1994, p. 38. [8] V.V. Uglov, V.V. Khodasevich, N.N. Cherenda, I.V. Kasko, V.A. Kutsanov, Surf. Coat. TechnoL 66 (1994) 283.
[9] M.A. E1 Khakani, H. Jaffrezic, G. Marest, N. Moneoffre, J. Tousset, NucI. Instrum. Methods B59/60 (1991) 751. [10] L. Claphan, Surf. Coat. Technol. 65 (1994) 24. [11] I.G. Brown, The Physics and Technology of Ion Sources, WileyInterscience, New York, 1989, p. 567. [12] I,G. Brown, W. Feinberg, J.E. Galvin, J. Appi. Phys. I0 (1988)4889.