Friction and Wear Behaviour of Ni Coated CNT

8/11/2019 Friction and Wear Behaviour of Ni Coated CNT

1/5

Wear 254 (2003) 12891293

Friction and wear behavior of electroless Ni-basedCNT composite coatings

L.Y. Wang a, J.P. Tu a,, W.X. Chen b, Y.C. Wang c, X.K. Liu c, Charls Olkc,D.H. Cheng d, X.B. Zhang a

a Department of Materials Science a nd Engineering, Zhejiang University, Hangzhou 310027, Ch inab Department of Chemistry, Zhejiang University, Hangzhou 31 0027, China

c Surface Engineering and Tribology Center, General Motors Corporation, 515N, Washington Avenue, Washington, DC, USAd Department of Environment and Chemical Engineering, Shanghai University, Shang hai 200027, China

Received 5 September 2002; received in revised form 30 December 2002; accepted 6 March 2003

Abstract

Ni-based carbon nanotube (CNT) composite coatings with different volume fraction (from 5 to 12 vol.%) of CNTs were deposited on

medium carbon steel substrates by electroless plating. The friction and wear behavior of the composite coatings were investigated using a

pin-on-disk wear tester under unlubricated condition. Friction and wear tests were conducted at a sliding speed of 0.0623 m s1 and at an

applied load of 20 N. The experimental results indicated that the friction coefficient of the composite coatings decreased with increasing the

volume fraction of CNTs due to self-lubrication and unique topological structure of CNTs. Within the range of volume fraction of CNTs

from 0 to 11.2%, the wear rate of the composite coatings showed a steadily decreasing trend with increasing volume fraction of CNTs.

Because of the conglomeration of CNTs in the matrix, however, the wear rate of the composite coatings increased with further increasing

the volume fraction of CNTs.

2003 Elsevier Science B.V. All rights reserved.

Keywords:Carbon nanotubes (CNTs); Electroless plating; Composite coating

1. Introduction

Electroless codeposition is one of the most impor-

tant techniques for producing composites of metallic and

non-metallic constituents. Coatings containing solid par-

ticles such as SiC, Al2O3, WC and diamond, etc. have

been developed for better wear resistance or dispersion

hardening [15]. Recently, carbon nanotubes (CNTs) are

increasingly attracting scientific and technological interest

by virtue of their unique chemical and physical properties

after discovered by Iijima[6].Many works on the physicalproperties, such as bending stiffness [7], Youngs modu-

lus[8], have been done using atomic force microscopy or

electronic transition microscopy. Treacy et al. [9] measured

the Youngs modulus of isolated nanotubules by measuring

the amplitude of their intrinsic thermal vibrations in the

TEM to find the average value of Youngs modulus to be

1.8 TPa. Wong et al.[7]used the atomic force microscopy

to determine the mechanical properties of the nanotubes to

Corresponding author. Tel.: +86-571-8795-2573;

fax: +86-571-8795-2573.

E-mail address:[email protected] (J.P. Tu).

find that they are stiff and tensile strength of carbon nan-

otubes reach 150 GPa. CNTs have been used as extremely

strong nano-tubular-reinforcements like fibers, for making

nano-composite[1012],which possess extraordinary high

strength. These nano-reinforcements could be used for im-

proving the tensile properties. Some recent researches have

investigated the tribological properties of CNT-reinforced

metallic matrix composites[13,14].It is found that the wear

resistance of the composites have been improved and the

friction coefficient decreases due to the effect of CNTs.

In the present work, Ni-based composite coatings withdifferent volume fraction of CNTs were deposited on 45#

steel substrates by electroless plating. The effect of the vol-

ume fraction of CNTs on friction and wear properties of the

Ni-based CNT composite coatings were investigated.

2. Experimental procedure

Multi-walled carbon nanotubes were prepared by chem-

ical catalytic vapor deposition (CCVD). The catalyst was

produced by concentrating cobalt nitrate and magnesium

nitrate solution to gelation and then grinding it to a fine

0043-1648/$ see front matter 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0043-1648(03)00171-6


2/5

1290 L.Y. Wang et al. / Wear 254 (2003) 12891293

powder after being sintered at 650 C. Carbon nanotubes

were obtained on the catalyst at 750 C with a flow rate

of acetylene 100 ml min1 and nitrogen 300 ml min1.

As-prepared CNT products were purified by immersing

them in concentrate nitric acid, then filtered and washed

with de-ionized water and dried at 120 C. CNT samples

were characterized by transmission electronic microscope(TEM, Philips 200UT). In order to improve the dispersion

of CNTs, the purified CNTs were mechanically ball milled

for 8 h with a planetary ball mill in an aether liquid at a

rotating speed of 430rev min1. The weight ratio of steel

balls to purified CNTs is 50:1. The CNTs have been rela-

tively shortened after ball milling. Then ultrasonic agitation

was used to disperse the shortened CNTs in the plating bath.

Ni-based composite coatings were deposited on test disk

specimens, which were fabricated by a low carbon steel with

a hardness of HB86, with a diameter of 15 mm by electro-

less plating. The electroless bath has the following compo-

sition: 20 g l1 NiSO46H2O, 26g l1 NaH2PO4, 1 5 g l

1

CH3COONa, 5 ml l1 HCOOH and 300mgl1 surfactant(cetyl-trimethylamine bromide). The bath temperature was

held at about 85 C and the pH value of the bath was main-

tained 4.6. The thickness of the Ni-based CNT composite

coatings were about 25m after depositing for 2 h. In or-

der to avoid the hydrogen brittleness, the composite coatings

were treated at 673 K for 2 h in vacuum before wear test.

Microstructure analysis of the composite coatings was iden-

tified by X-ray diffraction (XRD) (Cu K1, Philips X Pert

MPD). The surface morphology of the composite coatings

was evaluated using scanning electron microscopy (JEOL

JSM-5600LV) and atomic force microscopy. Microhardness

of the coatings was determined with a Vickers hardness in-denter (MT-3), using a load of 50 g.

Friction and wear properties of the coatings were investi-

gated using a pin-on-disk wear tester (MMW-1) under un-

lubricated condition.Fig. 1shows the schematic diagram of

the test machine. The spherical pins with a radius of 5 mm

were fabricated by a quenched-and-tempered medium car-

bon steel with a hardness of HB220. And the surface rough-

ness of the pins was about 4m center-line average (CLA).

Tests were conducted at a sliding speed of 0.0623 m s1 and

at load of 20 N in air (relative humidity 60%). Mass loss was

Fig. 1. Schematic diagram of pin-on-disk wear tester.

measured with an analytical balance at an interval of 15 min

throughout the tests. The coefficients of friction were cal-

culated by dividing the friction force which was recorded

on line via torque as measured by the strain gauge. In order

to take the repeatability into account, the test results for the

friction and wear under steady state sliding were obtained

from the average of three readings. The worn surfaces of theelectroless composite coatings on the disk specimens were

examined using scanning electron microscopy.

3. Results and discussion

3.1. Microstructure of composite coatings

Fig. 2ashows a TEM image of the purified carbon nan-

otubes. It can be found that the CNTs have central hollow

tubes, which are of typical multi-walled carbon nanotube

structure. The outer diameters of the most of CNTs range

from 20 to 40 nm. As shown inFig. 2a,the CNTs are much

longer in length than in their diameter, and most of CNTs en-

wind with each other, which has a negative effect on dispers-

ing of CNTs in the bath. In order to improve the dispersity

of CNTs in electroless bath, the CNTs were mechanically

milled. The TEM image of carbon nanotubes after being

Fig. 2. TEM images of: (a) purified CNTs; (b) ball milled CNTs.


3/5

L.Y. Wang et al. / Wear 254 (2003) 12891293 1291

Table 1

Volume fraction of CNTs and microhardness of electroless composite

coatings

CNT content in

bath (gl1)

Volume fraction of

CNTs in coatings (%)

Microhardness of

coatings (Hv 50)

0 0 1095

1.0 5.1 1130

2.0 10.0 1330

3.0 11.2 1524

4.0 12.5 1197

mechanical milled for 8 h is shown inFig. 2b. It is evident

from this figure that carbon nanotubes become shorter.

Compared with the density of NiP coating, the volume

fractions of CNTs in the composite coatings were calculated.

As shown inTable 1, the volume fraction of CNTs increased

sharply in the beginning and then slowly with the content

of CNTs in the plating bath.Fig. 3shows the XRD patterns

Fig. 3. XRD patterns of Ni-based CNT composite coatings before and

after treatment at 673K for 2 h.

Fig. 4. AFM image of electroless Ni-based CNT composite coating after

treatment at 673K for 2 h.

of the composite coatings with 5.1 vol.% CNTs before and

after treatment at 673 K for 2 h. It is found that their crystal

structures change from amorphous to typical crystalline

state, and Ni3P phase precipitates in the Ni matrix. Fig. 4

shows an AFM image of the surface of the as-prepared

Ni-based CNT composite coating with 10.0 vol.% CNTs,

revealing a relatively smooth surface morphology. Sur-

face roughness of the coatings ranged from 0.1 to 0.3m

center-line average (CLA). A SEM surface morphology of

the Ni-based composite coating with 10.0 vol.% CNT after

treatment at 673 K for 2 h is shown inFig. 5.It can be foundthat CNTs appear well dispersed and are embedded in the

nickel matrix. The microhardness of the composite coatings

with different volume fractions of CNTs are also listed in

Fig. 5. SEM surface morphology of Ni-based composite coating with

10.0vol.% CNTs.


4/5

1292 L.Y. Wang et al. / Wear 254 (2003) 12891293

Fig. 6. Variation of friction coefficient and wear rate of composite coatings

with volume fraction of CNTs.

Table 1. It is evident that the Ni-based CNT composite coat-

ings reveal higher hardness than NiP coating. The hardnessof the composite coatings increases with increasing the

volume fraction of CNTs, but then decreases with further

increasing the volume fraction. As shown in Table 1, the

hardness of the composite coating with 11.2 vol.% CNTs is

the highest.

3.2. Friction and wear

Fig. 6shows variation of steady-state wear rate and fric-

tion coefficient for composite coatings with volume fraction

of CNTs at a sliding speed of 0.0623 m s1 and at load of

20 N. The friction coefficient decreases with increasing thevolume fraction of CNTs in composite coatings. It is sug-

gested that an increase in surface fraction of CNTs reduces

the direct contact between the nickel matrix and steel pin.

Due to self-lubrication of CNTs, the short and tube shape

of the CNTs would more easily slide or roll between the

mating metal surface, thus resulting in the decrease in the

friction coefficient of the composite coatings.

The effect of volume fraction of CNTs on the wear rate

of the Ni-based composite coating is also shown in Fig. 6.

Within the range of volume fraction of CNTs from 0 to

11.2%, the wear rate of the composite coatings showed a

steadily decreasing trend with increasing volume fraction of

CNTs. When the volume fractions of CNTs were lower, the

favorable effects of CNTs on wear resistance are attribute

to their excellent mechanical properties and well dispersed

in the composite coating. However, increasing of volume

fraction of CNTs higher than 11.2% resulted in an increase

in wear rate. The fact is likely to be attributed to that the

conglomeration of CNTs in the matrix for the composite

coating with high volume fraction of CNTs decreases the

efficiency of the reinforcement of CNTs.

Fig. 7 shows worn surface morphology of the Ni-based

composite coatings with different volume fractions of CNTs

under unlubricated condition. Plastic deformation with

Fig. 7. Worn surface morphology of the Ni-based CNT composite coatings:

(a) 5.1 vol.% of CNTs in coating; (b) 12 vol.% of CNTs in coating.

grooves can be observed on the worn surface of the compos-

ite coating with lower volume fraction of CNTs (Fig. 7a).

With increasing the volume fraction of CNTs, the reunited

CNTs on the coating surface would flake away during thewear process. Cracking and spalling may also be seen on

the worn surface of the composite coating with higher vol-

ume fraction of CNTs (Fig. 7b),indicating that the peeling

of reunited CNTs lead to an increase in wear loss.

4. Conclusions

Ni-based CNT composite coatings were deposited on a

medium carbon steel substrate by electroless plating. After

treatment at 673 K for 2 h, their crystal structures changed

from amorphous to typical crystalline state, and Ni3P phaseprecipitated in the Ni matrix. The results demonstrated that

Ni-based CNT composite coatings exhibited higher wear re-

sistance and lower friction coefficient than NiP electroless

coating under unlubricated condition. Due to self-lubrication

and unique topological structure of CNTs, the friction coef-

ficient of the composite coatings decreased with increasing

the volume fraction of CNTs. The wear rate of the compos-

ite coatings increased with increasing the volume fraction of

CNTs within the range from 0 to 11.2%, but then decreased

with further increasing the volume fraction. Because of con-

glomeration of CNTs in the matrix, cracking and spalling

occurred on the worn surface of the composite coatings with

higher volume fraction of CNTs during wear process.

Acknowledgements

This work was supported by the National Natural Science

Foundation of China (No. 20003009), the Special Founda-

tion of the Education Ministry of China for Young Teacher

(2002-350), Hi-Tech research and development program of

China (2002AA334020), the Special Fund of General Mo-

tors Corporation and the Open Fund of State Key Lab of

Solid Lubrication, to whom we are very grateful.


5/5

L.Y. Wang et al. / Wear 254 (2003) 12891293 1293

References

[1] E.C. Kedwaed, K.W. Wright, A.A.B. Tennett, The development of

electro-deposited composites for use as wear control coatings on

aero engines, Tribol. Int. 7 (1974) 221228.

[2] A.K. Sikder, D.S. Misra, D. Singhbal, S. Chakvavorty, Surface

engineering of metal-diamond composite coatings on steel substrates

using chemical vapor deposition and electroplating routes, Surf. Coat.

Technol. 114 (1999) 230234.

[3] L. Benea, P.L. Bonora, A. Borello, S. Martelli, Wear corrosion

properties of nano-structured SiC-nickel composite coatings obtained

by electroplating, Wear 249 (2002) 9951003.

[4] P.L. Ko, M.F. Robertson, Wear characteristics of electrolytic hard chr-

ome and thermal sprayed WC10Co4Cr coatings sliding against Al

Nibronze in air at 21 C and at 40 C, Wear 252 (2002) 880893.

[5] B.F. Levin, J.N. Dupont, A.R. Marder, The effect of second phase

volume fraction on the erosion resistance of metal-matrix compo-

sition, Wear 238 (2000) 160167.

[6] S. Iijima, Carbon nanotubes, Nature 354 (1991) 5658.

[7] E.W. Wong, P.E. Sheehan, C.M. Lieber, Nanobeam mechanics:

elasticity, strength, and toughness of nanorods and nanotubes, Science

277 (1997) 19711975.

[8] M.R. Falvo, G..J. Clary, R.M. Taylor, V. Chi Jr., F.P. Brooks, S.

Washburn, R. Superfine, Bending and buckling of carbon nanotubes

under larger strain, Nature 389 (1997) 582584.

[9] M.M.J. Treacy, T.W. Ebbesen, J.M. Gibson, Exceptionally high

Youngs modulus observed for individual carbon nanotubes, Nature

381 (1996) 678680.

[10] L.S. Schadler, S.C. Giannaris, P.M. Ajayan, Load transfer in carbon

nanotube epoxy composites, Appl. Phys. Lett. 73 (1998) 3842

3844.

[11] A.K. Sharma, R. Kalyanaraman, R.J. Narayan, S. Oktyabrsty, J.

Narayan, Carbon nanotube composite synthesized by ion-assis-

ted pulsed laser deposition, Mater. Sci. Eng. B 79 (2001) 123

127.

[12] L. Jin, C. Bower, O. Zhou, Alignment of carbon nanotubes in a

polymer matrix by mechanical stretching, Appl. Phys. Lett. 73 (1998)

11971199.

[13] J.P. Tu, Y.Z. Yang, L.Y. Wang, X.C. Ma, X.B. Zhang, Tribological

properties of carbon nanotube reinforced copper composites, Tribol.

Lett. 10 (2001) 225228.

[14] S.R. Dong, J.P. Tu, X.B. Zhang, An investigation of the sliding wear

behavior of Cu-matrix composite reinforced by carbon nanotubes,

Mater. Sci. Eng. A313 (2001) 8387.

Friction and Wear Behaviour of Ni Coated CNT

Documents

Transcript of Friction and Wear Behaviour of Ni Coated CNT