126 S. El-Khatib, A.Y. Shash, A.H. Elsayed and A. El-Habak

© 2017 Advanced Study Center Co. Ltd.

Rev. Adv. Mater. Sci. 52 (2017) 126-133

Corresponding author: S. El-Khatib, e-mail: Samah.elmetwally@fue.edu.eg

EFFECT OF CARBON NANO-TUBES, MICRO AND NANODISPERSIONS OF SiC AND Al2O3 ON THE MECHANICAL

AND PHYSICAL PROPERTIES OF PURE COPPER

S. El-Khatib1,2, A.Y. Shash2, A.H. Elsayed3 and A. El-Habak2

1Mechanical Engineering Dept., Future University in Egypt, Cairo, Egypt2Mechanical Design and Production Engineering Dept., Cairo University. Cairo, Egypt

3Powder Technology Lab., Central Metallurgical Research and Development Institute, Cairo, Egypt

Received: July 18, 2017

Abstract. This paper studies the physical and mechanical properties of pure copper powder withvarious reinforcement materials at different volume fractions. The used reinforcement materialsare carbon nanotubes CNT (0.5-2 wt.%) as nano particles, Al

2O

3 (1-4 wt.%), and SiC (1-4 wt.%) as

micro particles. Various characteristics were evaluated on the composite specimens such asmicrostructures, density, electrical conductivity, thermal conductivity, hardness, and compressionproperties to investigate the suitable reinforcement percentage that achieves the best physicaland mechanical properties. The micron-sized Al

2O

3 and SiC and nano sized CNT has shown an

enhancement on the mechanical and physical properties of the composite. The electrical andthermal conductivities were evaluated and the results have shown positive enhancements.

1. INTRODUCTION

The main objective of electro-technical materials isattaining the best combination of high strength andhigh electrical conductivity that could be crucial forsome application, like the use of wires in high fieldpulse magnets in ovens, winding wires, electricalcontact clamps, bearing and other applications. Itis known that the pure copper (99.9%) has high elec-tric and thermal conductivities, but the use of purecopper is often limited by its low strength andmachinability. Therefore, strengthening the materi-als by adding reinforcement and using it as a ma-trix in nano-composites in a way that doesn’t nega-tively affect the physical properties and in the sametime improves the mechanical properties is an im-portant subject.

CNTs are perfect reinforcements for advancedcomposite materials for numerous engineering ap-plications. They are characterized by several fea-tures including a Young’s modulus of more than 1

TPa, tensile strength of over 150 GPa and thermalconductivity of up to 6000 W/mK [1-4]. However,due to some challenges such as achieving goodhomogenous dispersion of CNTs inside metal ma-trices, the difficulty of bonding and reactions withthe metal matrices, and loss of CNTs during process-ing, widening their applications still needs a lot ofefforts [5-7].

In this regard, the current research work focuseson the dispersion of CNTs with pure copper matrix,which was the main subject of some previous re-ports [8-10]. Also some researches were concernedwith improving the mechanical properties (hardness,compression, etc.) [11-13], thermal and electricalconductivities [13] of pure copper [14-19]. Moreo-ver, some studies focused on powder metallurgytechnique for using ceramic powder (Al

2O

3 and SiC)

as reinforcements [20-22]. The effect of carbon nanotubes and nano aluminum oxide particles on theelectrical conductivity of copper nano composites

127Effect of carbon nano-tubes, micro and nano dispersions of SiC and Al2O

3 on the...

has been previously demonstrated [23]. The effectof sintering temperature on the mechanical proper-ties of a Cu/CNT nano-composite prepared via apowder metallurgy method has been also presentedby changing the sintering temperature, which provedthat the density of Cu-CNT will be decreased with ahigh mass fraction of CNTs that exhibited high po-rosity in sintered specimens. Considerable enhance-ment was obtained by increasing CNT mass frac-tion in copper matrix, evaluated by the Brinell hard-ness test, with various mass fractions of the CNTs[24]. Physical properties like thermal and electricalconductivities of multi-walled carbon nano-tubes/copper matrix nano-composites have also been stud-ied [25].

This paper presents the powder metallurgy tech-nique for the carbon nano-tubes and ceramics pow-der (Al

2O

3 and SiC) with microns grain sizes as re-

inforcements for pure copper powder in various per-centages optimized to achieve the best physicaland mechanical properties. Besides, the obtainedspecimens were investigated with various mechani-cal tests as well as microstructural investigations

(optical and Scanning Electron Microscope (SEM)),density, electrical conductivity, thermal conductiv-ity, hardness and compression strength.

2. EXPERIMENTAL PROCEDURES

In this work, powder metallurgy method was usedto obtain composite samples which consist of multi-walled carbon nano-tubes (MWCNTs) [with averagediameter: 10-40 nm, length: 1-25 m, purity byweight: 99% min and specific surface area: 150-250 m2/g] as a reinforcement to very fine pure cop-per powder (99.9%) with 2-3 microns particle size.It has been reported in many researches that mix-ing copper powder with carbon nano-tubes is a chal-lenge as they are easily separated from each other[11]. So, this paper investigates an effective way toform a mixture using chemical dispersant ascyclohyxane-C

6H

12 and paraffin wax as a lubricant

through compaction together in order to reduce fric-tion and form a suitable environment for mixing CNTin the copper powder. The mixing process was car-ried out using a stainless steel container in a SPEX

Fig. 1. Cu/CNT powder metallurgy method.

128 S. El-Khatib, A.Y. Shash, A.H. Elsayed and A. El-Habak

800 rpm mixer / mill- for one hour. After mixing, themixture was dried in an oven for one hour at about100 °C that allows to melt the wax and to let it mixwell with copper and CNT mixture. Then the mix-ture was compacted in a rectangular die made fromCr-Mo alloy steel (DIN W302). The die cavity had arectangular cross-section with 6x15 mm2 area. Thehydraulic uniaxial press machine was adjusted at acompaction pressure of 600 MPa to obtain the com-pacted specimens. The sintering process was car-ried out in a vacuum furnace at 1050 °C for 2 hours.The heating rate was adjusted at 4 °C / min till 250°C where the temperature was held constant for 30min to complete the debinding stage. Then, theheating rate was raised to 6 °C till the maximum.Then the specimens were cooled in the furnace.Fig. 1 shows the details of the whole powder metal-lurgy process.

On the other hand, the pervious process wasrepeated, but carbon nano tubes were replaced withceramic Al

2O

3 powder (60 microns particle size) with

various percentages from 1-4% wt. Moreover, theceramic Al

2O

3 powder was also replaced again with

SiC (10 microns particle size) with the same per-centages (1-4 wt.%). The obtained specimens wereexamined under different types of tests. For micro-structure investigation, the specimens were preparedusing standard grinding with 120, 220,400, 600, 800,1000, 1200, 2000, and 3000 grit SiC papers andthen, they were polished with 6 micron diamondpaste. Optical microscope (type Axioplan) was usedto illustrate microstructure features using digitalcamera type Cannon PC1049 fitted with ZICElenses. The microstructure of the polished sampleswas also investigated by Field emission scanningelectron microscope (FESEM; QUANTAFEG250,Holland. Moreover, the actual density of the sinteredcomposites was determined using Archimedes rule,using water as the floating liquid. The sintered speci-mens were weighed in air and in distilled water thentheir actual densities (

act.) were calculated accord-

ing to the following equation:

a

a W

W

W Wact .

, (1)

where Wa and W

w are the masses of the sample in

air and water, respectively. The theoretical density(

th) for the investigated composite was calculated

according to the following equation:

m m r rV V

th( ) ( ), (2)

where Vm and

m are the volume fraction and den-

sity of the matrix while Vr and

r are the volume

fraction and density of the reinforcement. The de-gree of porosity of the sintered compacts was cal-culated according to the following equation:

act . th . th . act . th .Porosity(%) 1 ( / ) ( ) / . (3)

The electrical conductivity was measured usinga four-terminal ohmmeter for high accuracy. Onepair of terminals measures voltage, while the otherpair measures current. This allows the ohmmeterto ignore the resistance of the second pair of termi-nals. Then, the resistance of the specimen was re-corded using the ohmmeter.

L AR/ , (4)

where: - electrical conductivity (1/(m), L - thedistance between the ohmmeter terminals, A - thearea of the surface that the ohmmeter is measuringcurrent across, R - electrical resistance of the speci-men.

The thermal conductivity was estimated from theelectrical conductivity using Wiedemann-Franz law

K LT , (5)

where: K - thermal conductivity (W/mK), - electri-cal conductivity (1/ (m), L - Lorenz number (2.45x10-8 W/k2), T - temperature (K).

Vickers hardness was measured at a load of 10Kgf and the time to make an indentation was 10seconds for all specimens. The reported Vickershardness values of the specimens represent theaverage of 5 readings of each sample. Compres-sion strength test of the investigated samples wasperformed using a micro-computer-controlleduniaxial universal testing machine [HT-9501. Thesamples used for compression tests were of a rec-tangular 8x8 mm2 cross-section and a height of 15mm. The applied cross-head speed of universal testmachine used in this study was 2 mm/min. Thetest was conducted at room temperature.

3. RESULTS AND DISCUSSION

This section presents and discusses the physicaland mechanical properties of the obtained sinteredcomposite such as hardness, mechanical durabil-ity, electrical conductivity, thermal conductivity andthe density. Fig. 2 shows the un-etched microstruc-ture of the pure copper sample. It is obvious thatthe black dots represent the voids while there is nosign of incomplete powder particle bonding.

Fig. 3 displays the un-etched microstructure ofsintered composite of pure copper with 0.5 wt.%CNT and 1.5 wt.% CNT. It is noticed that while in-creasing CNT percentage in copper matrix, its ho-

129Effect of carbon nano-tubes, micro and nano dispersions of SiC and Al2O

3 on the...

mogenous distribution inside the specimens hasbeen kept unharmed. Also, the figure shows thatCNT’s are well bonded to the copper grains, whichis expected to be an effective factor in improving themechanical and physical properties of the sinteredcomposites. Light areas indicate Cu matrix and darkgrey and cornered shapes indicate the reinforce-ment component CNT and voids, respectively.

Fig. 4 illustrates the microstructure of sinteredcopper with 1% wt. Al

2O

3 and 4% wt. Al

2O

3. It shows

Fig. 2. Optical micrograph of sintered pure copper.

Fig. 3. Optical micrographs of sintered pure Copper/0.5 wt.% CNT (a) and pure Copper/1.5 wt.% CNT (b).

Fig. 4. Optical micrographs of sintered pure copper/1 wt.% Al2O

3 (a) and pure copper/4 wt.% Al

2O

3 (b).

Fig. 5. Optical micrographs of sintering pure Copper/1 wt.% SiC (a) and pure copper/4 wt.% SiC (b).

that micron-sized Al2O

3 particles have a great effect

on the optical microstructure of copper compositesintered samples (Cu/ Al

2O

3), where it clearly ap-

pears with uniform homogenous distribution in thecopper matrix. Before the mixing process, the Al

2O

3

particle size was bigger than that of copper. How-ever, it can be inferred from the figure that during themixing process, the Al

2O

3 particles has become finer

with sufficient distribution. It might also be worthmentioning that grain growth has already occurredin the composite sintered samples in both imagesin Figs. 4a and 4b in a non-homogeneous mannerwhich is a characteristic of vacuum sintered Cumatrix composites.

Similarly, Fig. 5 shows the optical microstruc-ture of sintered pure copper with 1 wt.% SiC and 4wt.% SiC. In both micrographs of the figure, lightareas indicate Cu matrix, while dark grey areas in-dicate the reinforcement component SiC particleswhich are homogeneously dispersed in the Cu ma-trix. At higher percentage (4 wt.%) of SiC, the parti-

130 S. El-Khatib, A.Y. Shash, A.H. Elsayed and A. El-Habak

Fig. 6. SEM images of pure Copper material aftersintering.

Fig. 7. SEM images of sintered pure Copper/0.5 wt.% CNT (a) and pure Copper/1.5 wt.% CNTnanocomposites.

Fig. 8. SEM images of sintered pure Copper/1 wt.% Al2O

3 (a) and pure Copper/4 wt.% Al

2O

3 (b) micro-

composites.

cles penetrate the copper grains due to ductile na-ture of copper.

Fig. 6 shows the microstructure of pure coppersample obtained by SEM, which demonstratesclearly the particle diffusion bonding between cop-per-copper particles as a result of sintering undervacuum atmosphere for two hours at 1050 °C. Theimage shows the un-etched surface of the speci-men, where grain boundaries can be clearly ob-served. The surface defects that appear on the SEMimage of pure Cu figures refer to void content.

Fig. 7 demonstrates SEM images of Cu/0.5 wt.%CNT and Cu/1.5 wt.% CNT nanocomposites after

sintering. It can be noted that the obtained SEMmicrographs show that CNTs were uniformly dis-persed in the copper matrix and no considerableagglomeration of CNTs was noted during this ob-servation. The grain size was clearly affected bythe increase in CNT percentage.

Fig. 8 illustrates the SEM micrographs of Cu/1wt.% Al

2O

3 and Cu/4 wt.% Al

2O

3 micro-composites.

The Al2O

3 reinforcement particles show good homog-

enous distribution in the copper matrix at low con-centrations. There are a number of Al

2O

3 agglom-

eration and small number of pores on the Cu/4 wt.%Al

2O

3 micro-composites because Al

2O

3 has high

volume fraction of (4 wt.%). The copper/ Al2O

3 inter-

action has also aided in the formation of a new phase,that is, Cu AlO

2 which has been identified in the

gray areas by SEM-EDS of Cu/4 wt.% Al2O

3 sam-

ple.Fig. 9 illustrates the SEM micrographs of Cu/1

wt.% SiC and Cu/4 wt.% SiC micro-composites.The SiC reinforcement particles have a perfect ho-mogenous distribution in the copper matrix. Thereare a number of pores on the grain boundaries ofthe copper grains, and their sizes are very small inthe micro-composites due to mixing process. Thereare some SiC agglomerations at higher SiC massfractions (4 wt.%).

131Effect of carbon nano-tubes, micro and nano dispersions of SiC and Al2O

3 on the...

Fig. 9. Sintering SEM images of (a) pure Copper/1 wt.% SiC (b) pure Copper/4wt.% SiC micro-compositematerial after sintering.

Fig. 10. Relative density versus mass fraction ofCu/CNT, Cu/ Al

2O

3, and Cu/SiC sintered compos-

ites.

Fig. 11. Electrical conductivity versus mass frac-tion of Cu/CNT, Cu/ Al

2O

3, and Cu/SiC and pure

copper sintered samples.

The relative density of a composite, made bypowder metallurgy, is the most important param-eter which greatly affects its mechanical and physi-cal properties. Fig. 10 shows the relative densitiesof pure copper and copper composites with varioustypes of reinforcements. Generally, the compositespecimens have shown less relative density thanthat of pure Cu. It can be noted that the relativedensity of was initially slightly improved by usingCNT and SiC as reinforcement materials in coppermatrix and that it was decreased with increasingthe reinforcement mass fraction for (CNT, Al

2O

3,and

SiC). Also, the relative density of Cu/SiC has highvalues compared to other specimens where the Cu/2 wt.% CNT has the lowest value of relative density.Decreasing the density of the Cu composite, whilewas not intended in this study, still makes no nega-tive effects on other properties providing better solu-tion of weight reduction for the composite.

Fig. 11 demonstrates the electrical conductivityfor different types of specimens. It can be notedthat pure copper with CNTs (1 wt.%) has the bestelectrical conductivity compared to others speci-mens. Those results are better compared to thosepreviously reported [23]. Also, the electric conduc-tivity of sintered pure copper is slightly lower thanthe casting pure copper (60*10^6 s/m) because ofthe voids. Moreover, the (Cu/CNT) curve at regionfrom 1-1.5 wt.% has more electrical conductivity withrespect to pure copper. This is because the CNThas a high electrical conductivity, but this advan-tage is limited at a certain range of mass fricationpercentage according to the powder metallurgy tech-nique.

Fig. 12 represents the estimated thermal con-ductivity for all specimens. As it follows the electri-cal conductivity, it is obvious that pure copper withCNTs (1%) has the best thermal conductivity com-pared to others specimens. Also, the thermal con-

ductivity of sintered pure copper is slightly lowerthan the casting pure Copper (401 W/(m·K)) becauseof the voids. Moreover, the (Cu/CNT) curve at regionfrom (1%-1.5%) wt.% mass fraction has more ther-mal conductivity compared to pure copper.

132 S. El-Khatib, A.Y. Shash, A.H. Elsayed and A. El-Habak

Fig. 12. Estimated thermal conductivity versus massfraction of Cu/CNT, Cu/ Al

2O

3 and Cu/SiC and pure

copper sintered samples.

Fig. 13. Hardness versus mass fraction of Cu/CNT,Cu/ Al

2O

3 and Cu/SiC and pure copper sintered pow-

der.

Fig. 14. Compression stress versus mass fractionof Cu/CNT, Cu/ Al

2O

3 and Cu/ SiC and pure copper

sintered powder.

The Vickers hardness test was carried out toinvestigate the apparent hardness of the specimensof Cu/CNT nano-composite, Cu/SiC and Cu/ Al

2O

3

micro-composite. In case of Cu matrix with CNTs,the apparent hardness has increased linearly untilCNTs (1.5 wt.%), while it has decreased after thispoint as shown in Fig. 13. Further increase in theCNT percentage has led to increasing the poreswhich negatively affects the hardness of the speci-mens. It can also be noted that the apparent hard-ness values of the Cu matrix with Al

2O

3 addition has

increased until 3% Al2O

3 and then remained the

same for higher Al2O

3 concentration. This may be

due to the miss-match of particle size of Al2O

3 and

Cu particle powders which leads to increasing thepores with higher Al

2O

3 percentage. Moreover, the

apparent hardness values of the Cu matrix with SiCaddition has increased until 2% SiC, while it hasdecreased after this point . This may be becauseSiC is partially soluble in the matrix at the sinteringtemperatures used in the study, which increasesthe Si and C level in the matrix.

Fig. 14 shows the compression yield stress re-sults of Cu/CNT, Cu/ Al

2O

3, and Cu/SiC and pure

copper sintered powder. It can be noted that thepure copper has low compression strength com-pared to most specimens. The compression yieldstrength of Cu/CNT was initially increased at 1 wt.%mass fraction and then it was decreased with in-creasing the CNT percentage. It can be noted thatthe fracture surface visual observation has showndarker appearances in case of CNT higher than 1wt.% addition as a result of the much increasedvolume fraction of CNTs which have very low den-sity compared to the copper matrix. In case of the

Cu/ Al2O

3 the compression stress was increased

gradually with increasing the Al2O

3 mass fraction.

This shows that alumina can be easily integratedinto copper matrix as was also previously shown inthe microstructure. On the other hand, the com-pression yield stress of Cu/SiC has shown the high-est values of all specimens. The yield stress hasincreased until 3 wt.% mass fraction and then de-creased with increasing SiC percentage.

4. CONCLUSION

Carbon nanotubes, Al2O

3 and SiC were individually

added as reinforcements to the copper matrix com-posites, which were successfully developed throughpowder metallurgy. Characterizing their microstruc-ture, physical, and mechanical properties was per-

133Effect of carbon nano-tubes, micro and nano dispersions of SiC and Al2O

3 on the...

formed. Results have shown that the proposedmanufacturing route was proven sufficient enoughto produce near full density copper composites.Sintering temperature at a vacuum furnace was usedto produce good sintered products at 2 hourssintering time and 1050 °C. The powder particle dif-fusion bonding can be seen clearly in the opticalmicroscope and SEM observations of the compos-ites. The specimens of the CNT with Nano-particlessize, Al

2O

3 and SiC Micro-particles size were pre-

sented as an enhancement to the mechanical andphysical properties, the electrical and thermal con-ductivities were measured and the results haveshown a good enhancement compared to pure cop-per.

REFERENCES

[1] S. Iijima // Nature 354 (1991) 56.[2] R.H. Baughman and A.A. Zakhidov // Science

80 (2000) 787.[3] Erik T.Thostenson, Zhifeng Ren and Tsu-Wei

Chou // Compos Sci Technol 61 (2001) 1899.[4] E. B. M. Esawi // Comp Sci Technol 68 (2008)

486.[5] Y. Chai, P. C. H. Chan, Y. Fu, Y. C. Chuang

and C. Y. Liu // IEEE Electron Device Lett. 29(2008) 1001.

[6] K. T. Kim, J. Eckert, S.B. Menzel,T. Gemming and S. H. Hong // Appl. Phys.Lett. 92 (2008) 3.

[7] M. R. R. A. S. Muhsan, F. Ahmad and N. M.Mohamed // Appl. Mech. Mater. 495(2014) 11.

[8] S. Arai and M. Endo // Int. J. Manuf. Eng.2013 (2013).

[9] A. S. Muhsan, F. Ahmad, N. M. Mohamed,P. S. M.r M. Yusoff and M. R. Raza //International Journal of ManufacturingEngineering 2013 (2013), Article ID 386141.

[10] A. S. Muhsan, F. Ahmad and N. M.Mohamed// J. Nano-engineering Nanomanufacturing3 (2013) 248.

[11] V. T. Pham, H. T. Bui, B. T. Tran, V. T.Nguyen, D. Q. Le, X. T. Than, V. C. Nguyen,D. P. Doan and N. M. Phan // Adv. Nat. Sci.Nanosci. Nanotechnol. 2 (2011) 015006.

[12] K. T. Kim, S. I. Cha and S. H. Hong // Mater.Sci. Eng. A 448–451 (2007) 46.

[13] S. H. H. W.M. Daoush, B.K. Lim, C.B. Moand D.H. Nam // Materials Sci. Eng. A513(2009) 247.

[14] K. Chu, H. Guo, C. Jia, F. Yin, X. Zhang,X. Liang and H. Chen // Nanoscale Res. Lett.5 (2010) 868.

[15] S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi,A. Kawasaki and T. Tsukada // Scr. Mater. 63(2010) 375.

[16] Y. Feng and S. L. Burkett // Comput. Mater.Sci. 97 (2015) 1.

[17] S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi,A. Kawasaki and T. Tsukada // Scr. Mater. 63(2010) 375.

[18] K. Chu, H. Guo, C. Jia, F. Yin, X. Zhang,X. Liang and H. Chen // Nanoscale Res. Lett.5 (2010) 868.

[19] Y. Feng and S. L. Burkett // Comput. Mater.Sci. 97 (2015) 1.

[20] M. Phillips and J. Porter // Advances inpowder metallurgy and particulate materials3(13) (1995) 31.

[21] S. M. Uddin, T. Mahmud, C. Wolf, C. Glanz,I. Kolaric, C. Volkmer, H. H.ller,U. Wienecke, S. Roth and H. J. Fecht //Compos. Sci. Technol. 70 (2010) 2253.

[22] V. Pantsyrny, A. Shikov, N. Khlebova,V. Drobishev, N. Kozlenkova, M. Polikarpova,N. Belyakov, O. Kukina and V. Dmitriev //IEEE Trans. Appl. Supercond. 20 (2010)1614.

[23] M. A. Ramadan // Research and Education inMechatronics 3 (2014) 2.

[24] V. T. Pham, H. T. Bui, B. T. Tran, V. T.Nguyen, D. Q. Le, X. T. Than, V. C. Nguyen,D. P. Doan and N. M. Phan // Adv. Nat. Sci.Nanosci. Nanotechnol. 2 (2011) 015006.

[25] P. G. Koppad, H. R. A. Rama, C. S. Ramesh,K. T. Kashya, and R. G. Koppad // J. AlloysCompd. 580 (2013) 527.