Effect of electrical current on tribological property of
Cu matrix composite reinforced by carbon nanotubes
XU Wei1, 2, HU Rui1, LI Jin-shan1, FU Heng-zhi1
1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China;
2. Engineering School, Shanxi Datong University, Datong 037003, China
Received 25 September 2010; accepted 5 January 2011
Abstract: Cu matrix composite reinforced with 10% (volume fraction) carbon nanotubes (CNTs/Cu) and pure Cu bulk were prepared
by powder metallurgy techniques under the same consolidation processing condition. The effect of electrical current on tribological
property of the materials was investigated by using a pin-on-disk friction and wear tester. The results show that the friction
coefficient and wear rate of CNTs/Cu composite as well as those of pure Cu bulk increase with increasing the electrical current
without exception, and the effect of electrical current is more obvious on tribological property of pure Cu bulk than on that of
CNTs/Cu composite; the dominant wear mechanisms are arc erosion wear and plastic flow deformation, respectively; CNTs can
improve tribological property of Cu matrix composites with electrical current.
Key words: CNTs/Cu composite; pure Cu bulk; electrical current; tribological property
1 Introduction
Carbon nanotubes (CNTs) have attracted interest in
the field of carbon fiber materials by virtue of their
unique chemical and physical properties since they were
discovered by IIJIMA [1] and CHEN et al [2]. Their high
strength, good self-lubricancy, specific modulus [3] and
unique conductivity [4] along with other properties have
led to the use of CNTs as extremely strong nano-tubular-
reinforcements to make nano-composites, which possess
extraordinary performance [5−7]. The super-strong
composites reinforced with CNTs for the next-generation
spacecraft have been investigated in NASA of USA [8].
It has been reported that addition of solid
lubrication particles into a metal matrix can improve not
only the anti-friction properties, but also wear resistance
properties [9−11]. The tribological properties of Cu
matrix composite reinforced by CNTs have been
investigated by DONG et al [12] and TU et al [13],
showing that the friction coefficient of the composite
decreases and the wear resistance is improved due to the
effect of CNTs. This work indicates that the CNTs in the
composite are not damaged during the composite
preparation and play a strengthening and toughening role
in the metal matrix composites.
Cu matrix composites possess the properties of
copper, namely, excellent thermal and electrical
conductivities, and are widely used as electrical contact
materials in many applications [14]. Although most
investigations have focused on the tribological property
of the Cu matrix composites reinforced by CNTs, the
effects of electrical current on the tribological property of
the composites have been reported in very few studies. In
conventional Cu matrix composites, with the increase of
reinforcement content, their electrical and thermal
conductivities are declined. Because of their superior
physical property and tribological property, CNTs offer
tremendous opportunities for the development of
fundamentally new electrical contact material system.
In this work, we report the effects of electrical
current on tribological property of Cu matrix composite
reinforced by CNTs. It has been anticipated that the
composite would have excellent tribological property
with electrical current.
2 Experimental
2.1 Preparation of composites
The multi-walled carbon nanotubes (CNTs) used in
Foundation item: Project (2007CB607603) supported by the National Basic Research Program of China
Corresponding author: HU Rui; Tel: +86-29-88491764; E-mail: rhu@nwpu.edu.cn
DOI: 10.1016/S1003-6326(11)61001-7
XU Wei, et al/Trans. Nonferrous Met. Soc. China 21(2011) 2237−2241 2238
this work were provided by Chengdu Organic Chemicals
Co., Ltd., Chinese Academy of Sciences. The diameter of
CNTs was less than 8 nm, the length was 10−30 µm and
the purity was 95%. In order to improve the interfacial
strength and the dispersion, the CNTs were subjected to a
treatment in the mixture of nitric acid and vitriolic.
The composites were fabricated by the powder
metallurgy technique. The powders of copper and CNTs
were mixed and milled for 5 h in an organic liquid with a
planetary ball mill machine. After mixing, the powder
mixture (Fig. 1(a)) was first cold pressed at 200 MPa,
and then sintering was carried out at 850 °C in vacuum
atmosphere for 5 h. After the specimens cooled to room
temperature, a second pressing at 600 MPa and a second
sintering were performed. For comparison, parallel
compacts made from pure copper powders were
consolidated under the same conditions applied for
CNTs/Cu composites. The sintered materials were
machined into the specimens of d10 mm×25 mm to fit
into the sample holder of the wear tester. All specimens
were polished and degreased with acetone before every
experiment. Figure 1(b) shows a SEM image of copper
matrix composites reinforced with 10% (volume fraction)
CNTs. It can be found that the CNTs appear dispersive
and are fully embedded in the copper matrix. Physical
Fig. 1 TEM images of powder mixture of copper and CNTs (a)
and copper matrix composite reinforced with 10% CNTs (b)
characteristics of the CNTs/Cu composite are listed in
Table 1.
Table 1 Physical characteristics of CNTs/Cu composite
Density/
(g·cm−3)
Hardness,
HB
Compactness/
%
Thermal conductivity/
(W·m−1·K−1)
7.6 54 96 326.026
2.2 Measurements
The friction and wear tests were performed by using
a HST100 pin-on-disk friction and wear tester. The
experiments were conducted at a sliding speed of 5 m/s
and at a applied loads of 20 N. The counterparts in the
experiments were fabricated from the alloy of Cu-0.5Cr.
The coefficient of friction was calculated by dividing the
friction force which was recorded on line via torque as
measured by the strain gauge, by the applied load. In
order to take repeatability into account, the test results of
friction coefficient and wear rate under steady-state
sliding were obtained from the average of three readings.
The worn surfaces of the tested samples were observed
by using JSM−56102V scanning electron microscope.
3 Results and discussion
3.1 Friction coefficient and wear rate
Figures 2 and 3 show respectively the changes of
friction coefficient and wear rate against electrical
current for pure Cu bulk and CNTs/Cu composite. It is
clear that the friction coefficient and wear rate increase
gradually with the increase of electrical current. The
surface of solid object has a certain degree of roughness,
so the actual contact area between the sample and
counterpart is only a small fraction of the apparent area.
The electrical current is constricted when it passes
through a contact spot [15]. As a result, the electrical
Fig. 2 Variation of friction coefficient of pure Cu bulk and
composites with electrical current
XU Wei, et al/Trans. Nonferrous Met. Soc. China 21(2011) 2237−2241 2239
Fig. 3 Variation of wear rate of pure Cu bulk and composites
with electrical current
current through the individual contact spot may become
the statistical average value after several times. In the
course of friction and wear with electrical current the
total power loss is the sum of mechanical loss and
electrical loss, and the combined effects cause extremely
high local temperatures. The pure Cu bulk is partially
melted and the integrity of lubricating film on the surface
of CNTs/Cu composite is damaged, and finally the
roughness of worn surface is advanced. Larger electrical
current brings more electrical heat, so as that the samples
become rougher, which explains the friction coefficient
increasing gradually with the increasing electrical current.
Otherwise, the higher and higher local temperature
intenerates the specimen surface, resulting in increasing
wear rate with the increase of electrical current.
It is also noted that the friction coefficient and wear
rate of CNTs/Cu composite are lower than those of pure
Cu bulk prepared by the same route. During friction and
wear process, superficial CNTs in composites
accumulate and gradually spread out at the contact
interface, and are milled into debris under friction forces,
forming a layer of self-lubricating film. This film
changes the nature of contact from metal-metal to
lubricating film-metal, improves lubricating property,
reduces the shearing intensity and decreases the friction
coefficient of composite. In addition, the decrease of
electrical resistivity with the addition of CNTs leads to
the decline of electrical power loss and the friction
surface temperature. As a result, the adhesive wear
between composite and counterpart is inhibited.
From Fig. 2 and Fig. 3, we can also see that the
variation curve of CNTs /Cu composites is gentler than
that of pure Cu bulk. It is explained that the effect of
electrical current is slighter on CNTs/Cu composites than
on pure Cu bulk. CNTs have high thermal stability, so
using CNTs reinforced Cu matrix composites can
decrease the effects of electrical arc heat and friction heat
on the composites, and ultimately improve the friction
and wear properties with electrical current of Cu matrix
composites.
3.2 Worn morphology
Figure 4 presents the worn morphologies of pure Cu
bulk and CNTs /Cu composite with different electrical
currents. The worn surfaces of pure Cu bulk reveal not
only intensive abrasive and adhesive wear with deep
grooves but also a mass of oxide and melted dripping, as
shown in Figs. 4(a), (c) and (e). Figure 5(a) shows an
EDS analysis of the worn surface of pure Cu bulk with
electrical current of 20 A, in which the existence of
oxygen element demonstrates that pure Cu bulk is
oxidized in the action of high temperature caused by the
electrical and frictional heat. Joule heat released on the
contact spots leads to intensification of wear of the
materials under the action of an electrical current. In
addition, the increase of electrical current results in an
increase in the melting dripping and deformation for pure
Cu bulk, the surface of pure Cu bulk is destroyed more
severely. It is suggested that the increase of electrical
current came into being more heat that cannot be
released so as to cause higher local temperatures [16].
The pure Cu bulk is intenerated and deformed by friction
force at high temperature.
In comparison, for the CNTs/Cu composite little of
oxide and melted dripping are seen on the worn surface,
as shown in Figs. 4(b), (d) and (f). Plastic deformation
with characteristic of wear scars and a little degree of
flake formation can be observed on the worn surface of
CNTs/Cu composite. Additionally, cracking of the flake
layer may also be seen on the worn surface. The flake
formation occurs when a highly strain-hardened layer
forms on the specimen surface after sliding wear. The
combination of thermal and mechanical shock creates
condition for the development of rupture and failure of
the surface layer. Larger electrical current causes higher
Joule heat, resulting in an increase of temperature which
inhibits the action of the film to remain tightly bound to
the matrix. The film layer becomes flaky and
discontinuous and is easily removed so that wear takes
place further. Plastic flow deformation is the principal
wear mechanism, while cracking is predominant for
composites. Figure 5(b) shows EDS analysis of scanning
the worn surface of CNTs/Cu composite with electrical
current of 20 A. Absence of oxygen element explains that
oxidation is held back, and the composite has high
conductivities of electricity and heat due to its special
microstructure.
XU Wei, et al/Trans. Nonferrous Met. Soc. China 21(2011) 2237−2241 2240
Fig. 4 SEM images of worn surfaces with different electrical currents: (a) Pure Cu bulk, 20 A; (b) CNTs/Cu, 20 A; (c) Pure Cu bulk,
40 A; (d) CNTs/Cu, 40 A; (e) Pure Cu bulk, 80 A; (f) CNTs/Cu, 80 A
Fig. 5 EDS analysis of worn surfaces: (a) Pure Cu bulk, 20 A; (b) CNTs/Cu composite, 20 A
XU Wei, et al/Trans. Nonferrous Met. Soc. China 21(2011) 2237−2241 2241
4 Conclusions
1) Friction coefficient and wear rate of CNTs/Cu
composite and pure Cu bulk increase gradually with the
increase of electrical current. The effects of electrical
current are more obvious on tribological property of pure
Cu bulk than on that of CNTs/Cu composite. For pure Cu
bulk, the dominant wear mechanism is electrical erosion
wear, while for CNTs/Cu composite is plastic flow
deformation.
2) The anti-friction and wear resistance properties
of CNTs/Cu composite are more excellent than those of
pure Cu bulk prepared by the same route. CNTs have
high thermal stability, decreasing the effects of electrical
arc heat and friction heat on the composites, and
ultimately improving the friction and wear properties
with electrical current of Cu matrix composites.
References
[1] IIJIMA S. Helical microtubules of graphitic carbon [J]. Nature, 1991,
354(6348): 56−58.
[2] CHEN W X, TU J P, WANG L Y, GAN H Y, XU Z D, ZHANG X B.
Tribological application of carbon nanotubes in a metal-based
composite coating and composites [J]. Carbon, 2003, 41(2):
215−222.
[3] KENNETH K H W, MARTIN Z A, JEFFERY L H, SABAHUDIN H,
JOHN H T L, WANKEI W. The effect of carbon nanotube aspect
ratio and loading on the elastic modulus of electrospun poly(vinyl
alcohol)-carbon nanotube hybrid fibers [J]. Carbon, 2009, 47(11):
2571−2578.
[4] WANG Juan, FENG Yi, LI Shu, LIN Shen. Influence of graphite
content on sliding wear characteristics of CNTs-Ag-G electrical
contact materials [J]. Transactions of Nonferrous Metals Society of
China, 2009, 19(1): 113−118.
[5] SCHADLER L S, GIANNARIS S C, AJAYAN P M. Load transfer in
carbon nanotube epoxy composites [J]. Applied Physics Letter, 1998,
73(26): 3842−3844.
[6] ZHOU S M, ZHANG X B, DING Z P, MIN C Y, XU G L, ZHU W
M. Fabrication and tribological properties of carbon nanotubes
reinforced Al composites prepared by pressureless infiltration
technique [J]. Composites Part A, 2007, 38(2): 301−306.
[7] HONG W T, TAI N H. Investigations on the thermal conductivity of
composites reinforced with carbon nanotubes [J]. Diamond and
Related Materials, 2008, 17(7−10): 1577−1581.
[8] FILES B S, NASA/JSC carbon nanotube project status [J]. Journal of
Nanoparticle Research, 1999, 1(4): 507−509.
[9] HASHEMI H N, BLUCHER J T, MIRAGEAS J. Friction and wear
behavior of aluminum-graphite composites as a function of interface
and fiber direction [J]. Wear, 1991, 150(1−2): 21−39.
[10] ZHANG Mei-juan, YANG Xiao-hong, LIU Yong-bing, CAO Zhan-yi,
CHENG Li-ren, PEI Ya-li. Effect of graphite content on wear
property of graphite/Al2O3/Mg-9Al-1Zn-0.8Ce composites
[J]. Transactions of Nonferrous Metals Society of China, 2010, 20(2):
207−211.
[11] AKHLAGHI F, BIDAKI A Z. Influence of graphite content on the
dry sliding and oil impregnated sliding wear behavior of Al
2024-graphite composites produced by in situ powder metallurgy
method [J]. Wear, 2009, 266(1−2): 37−45.
[12] DONG S R, TU J P, ZHANG X B. An investigation of the sliding
wear behavior of Cu-matrix composite reinforced by carbon
nanotubes [J]. Material Science and Engineering A, 2001, 313(1−2):
83−87.
[13] TU J P, YANG Y Z, WANG L Y, MA X C, ZHANG X B.
Tribological properties of carbon-nanotube-reinforced copper
composites [J]. Tribology Letters, 2001, 10(4): 225−228.
[14] TANG Y P, LIU H Z, ZHAO H J, LIU L, WU Y T. Friction and wear
properties of copper matrix composites reinforced with short carbon
fibers [J]. Materials & Design, 2008, 29(1): 257−261.
[15] SHINCHI A, IMADA Y, HONDA F, NAKAJIMA K. Electric contact
surface of Pd-plated metal in organic gas/air atmospheres [J]. Wear,
1999, 230(1): 78−85.
[16] FENG Y, ZHANG M, XU Y. Effect of the electric current on the
friction and wear properties of the CNT-Ag-G composites [J]. Carbon,
2005, 43(13): 2685−2692.
电流对碳纳米管增强铜基复合材料
载流摩擦学性能的影响
许 玮 1, 2, 胡 锐 1, 李金山 1, 傅恒志 1
1. 西北工业大学 凝固技术国家重点实验室,西安 710072;
2. 山西大同大学 工学院,大同 037003
摘 要:采用粉末冶金方法在相同的工艺条件下制备纯铜和碳纳米管含量为 10%(体积分数)的铜基复合材料。在
一种销盘式载流摩擦磨损试验机上考察了不同电流条件下 2种材料的载流摩擦磨损性能。结果表明:纯铜和铜基
复合材料的摩擦系数和磨损率均随电流的增大而增大,但是电流对纯铜材料的影响更加显著;纯铜材料的主导磨
损机制是电弧烧蚀磨损,而铜基复合材料的主导磨损机制是塑性流动变形;碳纳米管可以改善铜基复合材料的载
流摩擦磨损性能。
关键词:碳纳米管铜基复合材料;纯铜;载流;摩擦学性能
(Edited by YANG Hua)
本文档为【金属基碳纳米管复合材料3】,请使用软件OFFICE或WPS软件打开。作品中的文字与图均可以修改和编辑,
图片更改请在作品中右键图片并更换,文字修改请直接点击文字进行修改,也可以新增和删除文档中的内容。
该文档来自用户分享,如有侵权行为请发邮件ishare@vip.sina.com联系网站客服,我们会及时删除。
[版权声明] 本站所有资料为用户分享产生,若发现您的权利被侵害,请联系客服邮件isharekefu@iask.cn,我们尽快处理。
本作品所展示的图片、画像、字体、音乐的版权可能需版权方额外授权,请谨慎使用。
网站提供的党政主题相关内容(国旗、国徽、党徽..)目的在于配合国家政策宣传,仅限个人学习分享使用,禁止用于任何广告和商用目的。