The improvement in the wear properties of GCr15QBe2 wear pairs by ion implantation

The improvement in the wear properties of GCr15QBe2 wear pairs by ion implantation

Materials Science and Engineering, 90 (1987) 291-295 291 The Improvement in the Wear Properties of GCrl5-QBe2 Wear Pairs by Ion Implantation* ZHAO J...

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Materials Science and Engineering, 90 (1987) 291-295

291

The Improvement in the Wear Properties of GCrl5-QBe2 Wear Pairs by Ion Implantation* ZHAO JIE a, SU YAWENa, LU GUANGYUANa, LIU FU RUN a, YE WEIYIa and LI WANGb

aDepartment of Physics, Tianjin Normal University, Tianjin (China) bNorth China Research Institute, Tianjin (China) (Received July 10, 1986)

ABSTRACT

We have studied the influence o f overlapping nitrogen ion implantation and recoil implantation on the wear resistance o f GCr15 bearing steel and QBe2 beryllium bronze wear pairs. GCr15 bearing steel specimens were implanted with nitrogen ions ( N +) at 120, 70 and 30 k e V in sequence at the same fluence o f I X 10 I7 ions cm -z. For the recoil case, after the surface o f the GCr15 steel specimens had been coated with 300 ~ o f chromium, nitrogen implantation was p e r f o r m e d at energies o f 30 and 70 k e V at a fluence o f 2 X 1017 ions cm -2. A series o f wear measurements were carried o u t on the specimens under two different loads applied with a pin-on-disk wear tester. During the wear testing, an unimplanted QBe2 beryllium bronze pin was fixed on the tester as the pin and the implanted GCr15 bearing steel specimen was used as the disk, as usual. In the recoil implantation o f GCr15 steel specimens, the improvement in wear resistance is remarkable for both GCr15 and QBe2. The wear resistance o f GCr15 steel specimens subjected to overlapping implantation, however, did n o t change significantly. In order to investigate the microstructure, Auger electron spectroscopy was used to measure the depth profile o f the implanted nitrogen and electron spectroscopy for chemical analysis was also performed. On the surface o f the specimens, Cr20s and various nitrides were found. The existence o f these c o m p o u n d s

*Paper presented at t h e International Conference on Surface Modification of Metals by Ion Beams, Kingston, Canada, July 7-11, 1986. 0025-5416/87/$3.50

is thought to be the main reason for the imp r o v e m e n t in wear properties.

1. INTRODUCTION Several papers on the modification of the wear of steel-steel and b r o n z e - b r o n z e cont act by ion implantation have been published in recent years [1-4]. Sometimes, however, t he steel-bronze wear pair is used in technological processes. Therefore, it is very i m p o r t a n t to improve t he wear resistance of the steel-bronze system. Ion implantation was shown to be an effective w ay of modifying the wear resistance for m a n y wear pairs. Some results of t he wear tests using G C r l 5 bearing steel implanted with nitrogen ions (N +) and unimplanted QBe2 beryllium bronze are r e p o r t e d in t he present paper. These results are com pared with t he results of wear tests between unimplanted steel and QBe2 beryllium bronze. In the present experi m ent the G C r l 5 steel specimens were b o m b a r d e d with an ion beam in two di fferent ways. In one case the specimens were directly implanted with nitrogen ions (N+); in the ot her case the specimens were first coated with 300 fl, of c h r o m i u m and t h e n implanted with nitrogen ions (N +) (recoil implantation). In order to obtain a u n i f o r m distribution, the nitrogen ion implantation was p e r f o r m e d using three different energies, namely 120, 70 and 30 keV sequentially. After nitrogen ion implantation, the wear test, Auger elect r o n spectroscopy (AES) and electron spect r o s c o p y for chemical analysis (ESCA) were carried o u t to investigate t he influence o f t he surface modification on the wear resistance and its mechanism. © Elsevier Sequoia/Printed in The N e t h e r l a n d s

292 2. E X P E R I M E N T A L M E T H O D S

(1) For overlapping nitrogen ion (N ÷) implantation the GCrl5 bearing steel specimens were implanted with nitrogen ions at 120, 70 and 30 keV in sequence with the same fluence of 1 X 1017 ions cm -2 to obtain a relatively uniform nitrogen ion distribution over the penetrative depth of the ions into the surface of the specimens. (2) For the recoil implantation the G C r l 5 steel specimens were coated with 300 A of chromium and then implanted with nitrogen ions (N ÷) at energies of 30 and 70 keV with a fluence of 2 X 1017 ions cm -2. The reason for choosing these energies in the recoil implantation case is as follows. (a) In order to obtain good mixing between the chromium coating and the iron matrix, the energy chosen should correspond to the maximum de/dp in the universal curve of de/dp vs. e, to reach a high nuclear stopping power. (b) The mean projected range of nitrogen ions (N ÷) should be nearly equal to the thickness of the chromium film coating, to obtain a mixing layer between the chromium and iron. (c) Because of the effect of sputtering, some chromium is lost from the surface. The thickness of the chromium film coating therefore has to be thick enough. When the above three factors (a)-(c) were taken into account, a suitable energy was f o u n d to be about 30 keV in accordance with the Lindhard-Scharff-Schi#tt t h e o r y [5]. To

compare the effect of implantation at different energies, a 70 keV ion beam was also used. (3) Next let us consider the conditions under which the wear tests were carried out. They were performed with a pin-on-disk wear tester [6]. The pin of QBe2 beryllium bronze was 2 mm in diameter, with a taper of 120 ° and an initial diameter of 0.20 mm. The pins were loaded with 400 gf in the axial direction and for some measurements the load was increased to 1200 gf. For the disk the speed of rotation was 640 rev min -1. A light machine oil lubricant such as sewing machine oil was used in all the tests. (4) All specimens were analysed using a multifunctional electron spectrometer (PHI550) by means of AES and ESCA.

3. R E S U L T S

3.1. Wear test results The wear curve between the GCr15 steel disk implanted with nitrogen and the unimplanted QBe2 beryllium bronze is shown in Fig. 1 and indicates that the wear of the QBe2 beryllium bronze pin was obviously reduced by implantation of the steel disk. Under a metallographic microscope, it could be seen that there was some adhesion of QBe2 on the unimplanted GCr15 disk, whereas there was no obvious adhesion on the nitrogen-implanted disks. From this, we concluded that nitrogen ion (N ÷) implantation improved the adhesive wear.

70 60

/"

/

o/

2

50 40 30 20 Io

/

o X--y J',

X ~ X X I X XI000 2000 Distance of weor (m) 4 0 0 gf -"!-1200 gf - -

Fig. 1. Wear curve o f a QBe2 pin o n a disk a f t e r overlapping n i t r o g e n ion (N +) i m p l a n t a t i o n : e, pin o n a n u n i m p l a n t e d disk; X, p i n o n a n o v e r l a p p e d i m p l a n t e d disk.

I.,

l~x----

--------x~

_ _ - - x ~ 7 A • t 1000 I 2000 Distence of weor (m) 4 0 0 gf D I., 1200 gf - -

A-

Fig. 2. Wear curve o f a QBe2 pin o n a disk a f t e r n i t r o g e n ion (N ÷) recoil i m p l a n t a t i o n : o, pin o n a n u n i m p l a n t e d disk; X, p i n o n a disk c o a t e d w i t h chrom i u m a n d i m p l a n t e d w i t h 30 keV n i t r o g e n ions; A, pin o n a disk c o a t e d w i t h c h r o m i u m and i m p l a n t e d w i t h 70 keV n i t r o g e n ions.

293 TABLE 1 The wear modification coefficient K for various specimens

Implantation conditions

Load

K

(gf)

Ion

Coating E n e r g y (keY)

Fluence (XlO 17

ions cm -2) N÷ N÷ N+ N÷ N÷ N+

Cr Cr Cr Cr

30 30 70 70 120, 70, 30 120, 70, 30

2 2 2 2 1 (each) 1 (each)

400 1200 400 1200 400 1200

5.0 2.1 4.3 11.0 8.0 14.5

K = (tan ~un)/(tan aim) is calculated in accordance with the slope of the straight-line part of the curves.

80

3oo~ 604

N+

s B _~ 4 0 -

Fig. 3. Micrographs o f t h e w e a r trace o n t h e surfaces o f s p e c i m e n s : (a) a w e a r trace o n t h e surface o f a specimen coated with chromium and implanted with n i t r o g e n ions (N +) at 30 keV; (b) a w e a r trace o n an unimplanted specimen.

o (D

2.00

Figures 2 a n d 3 s h o w t h a t t h e w e a r resista n c e s o f b o t h Q B e 2 b e r y l l i u m b r o n z e pins and G C r l 5 steel disks c o a t e d w i t h c h r o m i u m w e r e i m p r o v e d significantly. I t can b e observed f r o m t h e m i c r o g r a p h s in Fig. 3 t h a t t h e w e a r t r a c e o n u n i m p l a n t e d disks is v e r y o b v i o u s w i t h m a n y t r a c e lines; h o w e v e r , it is v e r y d i f f i c u l t t o f i n d a n y w e a r lines o n t h e r e c o i l - i m p l a n t e d disks. The wear modification coefficients of the pin f o r various i m p l a n t a t i o n c o n d i t i o n s are listed in T a b l e 1, w h e r e t a n aun a n d t a n aan stand f o r t h e slopes o f t h e straight-line p a r t o f curves f o r t h e u n i m p l a n t e d s p e c i m e n s a n d i m p l a n t e d s p e c i m e n s respectively.

8120

[0,50

Sputlering time (min)

Fig. 4. AES profile analysis of GCrl5 steel specimens after nitrogen ion (N ÷) recoil implantation.

3.2. The results obtained by Auger electron spectroscopy and electron spectroscopy for chemical analysis T h e AES profile results f o r s p e c i m e n s c o a t e d with chromium and bombarded with nitrogen ions (N ÷) at 30 keV are s h o w n in Fig. 4, f r o m which the extent of mixing of chromium and iron can b e f o u n d ; h o w e v e r , b e c a u s e o f t h e light m a s s o f n i t r o g e n , t h e m i x i n g o f chrom i u m a n d i r o n is o n l y slight. I n Fig. 5 t h e

294

profile for the overlapping nitrogen ion implantation can be seen. It indicates that the distribution of nitrogen is relatively uniform over a wide region. Therefore the overlapping implantation can be used in cases in which a uniform distribution of an implanted elements is required [7]. In addition, ESCA indicated that there is Cr2Os, CrN, (graphitic) carbon and iron in

60

~

v

I~-Fel

I

/

I

I

f-"--q_

..



various states in the implanted layer o f the specimen [8], as shown in Fig. 6. 4. DISCUSSION AND CONCLUSIONS

(1) After recoil implantation of GCr15 steel specimens, the improvement in wear resistance was remarkable for b o t h G C r l 5 steel and QBe2 beryllium bronze. However, for the GCr15 steel subjected to overlapping nitrogen ion implantation, the improvement in the wear resistance of the @Be2 pin slipping on the disk is obvious, b u t the wear resistance of the steel disk has not changed. In b o t h cases the adhesive wear was significantly improved. (2) With increasing ion energy (from 30 to 70 keV) the wear resistance of GCr15 steel specimens was hardly changed, b u t the depth for surface modification at 70 keV may be deeper than that at an implantation energy of 30 keV. (3) The wear behaviour of G C r l 5 - Q B e 2 wear pairs after nitrogen ion implantation varies with load. F r o m Figs. 1 and 2, it can be observed that the wear resistance of the pin under a load of 400 gf is better than that under a load of 1200 gf.

I

+ ~2o ~ too

~e.

2 ~ 40

° < t ~

c

~ 20

0.00

2.00

4.00 6.00 s.oo Sputtering time (rain)

io.oo

~2.00

Fig. 5. AES profile analysis of GCr15 steel specimens after overlapping nitrogen ion (N ÷) implantation at energies of 120 and 30 keV.

L..

Cr

LMM

~

//~

J /

,,,\

l:

,,.1

"c

Z

/ °

/

J

X

o,.

I I000

I

I 1 800

I I

I I 600

i I

-

--

/

J I 400

-/

i I

I I 200

\

i

B i n d i n g energy (eV)

Fig. 6. ESCA of GCr15 steel specimen coated with chromium and bombarded with nitrogen ions (N+).

295

(4) According to ESCA, there may be various reasons for the modification of specimens coated with chromium and implanted with nitrogen ions. Graphitic carbon could play the role of lubricant, and the existence of hard phases such as Cr2Os, CrN and FeN on the surface is probably the main reason for the improvement [9]. Since the load and lubricant conditions in our experiments were more severe than in normal practice, we believe that the wear resistance of G C r l 5 - Q B e 2 wear pairs could be greatly improved for practical uses b y nitrogen ion recoil implantation.

ACKNOWLEDGMENTS

We wish to thank Mr. Li Yongcan for his skill in the preparation of specimens and Mr. Luo Yingming for the ion implantation.

REFERENCES 1 C. Fuzhai, L. Hengde and Z. Xiaozhong, Nucl. Instrum. Methods, 209-210 (1983) 881. 2 S. Yawen, L. Guangyuan and L. Furun, Proc. Natl. C o n f on Electron Beam, Ion Beam and Laser Beam Methods, China, 1984. 3 A. Kujore, S. B. Chakrabortty, E. A. Starke and K. O. Legg, Nucl. Instrum. Methods, 182-183 (1981) 949. 4 S. Saritas, R. P. M. Procter, V. Ashworth and W. A. Grant, Wear, 82 (2) (1982) 233. 5 P. D. Townsend, J. C. Kelly and N. E. W. Hartley, Ion Implan ration, Sputtering and their Applications, Academic Press, New York, 1976. 6 J. K. Hirvonen, J. Vac. Sci. Technol., 15 (5) (1978) 1662. 7 J. K. Hirvonen, Proc. 1st Int. C o n f on Ion Beam Modification o f Materials, Central Research Institute of Physics, Budapest, 1978, p. 1753. 8 C. D. Wagner, Handbook o f E S C A , Perkin Elmer, 1979. 9 I. L. Singer, C. A. Carosella and J. R. Reed, Nucl. Instrum. Methods, 182-183 (1981) 923.