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Tribological characteristics of multiwalled carbon nanotubes and boron carbide particles reinforced Al2024 matrix composites
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 5762–5767
www.materialstoday.com/proceedings
ICMPC 2017
Tribological Characteristics of Multiwalled Carbon Nanotubes And Boron Carbide Particles Reinforced Al2024 Matrix Composites Mohamed Zakaullaa, Arjun.Rb, Muzakkir Ahmed Khanc, Izhar Hussein Khand, Nadeem Pashae. a
H.K.B.K.C.E, Bangalore, 560045, India b U.V.C.E, Bangalore, 560068, India H.K.B.K.C.E, Bangalore, 560045, India d H.K.B.K.C.E, Bangalore, 560045, India e H.K.B.K.C.E, Bangalore, 560045, India c
Abstract Wear and friction behavior of Al2024 monolithic alloy reinforced with 10wt% B4C particles and MWCNTs varied in 1wt% and 2wt% was investigated. The hybrid Al2024 composite were fabricated using stir casting technique. Experiment was performed using pin-on-disk wear testing machine against a steel disk of hardness Rc 60 under a load of 10N, 20N and 30N with sliding speed of 0.84m/sec. The tribological test results indicated that Al2024-10wt% B4C + 2%MWCNTs displayed lower friction coefficient and wear rate compared to Al2024-10wt% B4C + 1%MWCNTs, Al2024-10wt% B4C composite and Al2024 alloy. The worn surfaces were examined using high resolution scanning electron microscope © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 7th International Conference of Materials Processing and Characterization. Keywords: wear; friction; boron carbide; sliding speed: sliding distance.
1. Introduction Aluminium composites reinforced with nanotubes and nanoparticles are currently used in fields such as electronics, transport, aerospace, renewable energy and architectural structure [1-3]. The combination of unique properties of carbon nanotubes and auminium alloys have great potential in weight sensitive applications [4-5]. Zhou and coworkers [6] fabricated aluminium composites reinforced with CNTs using pressure infiltration technique performed at 800°C in N2 atmosphere. They indicated that CNTs are well distributed and embedded in Al matrix. * Corresponding author. E-mail address : [email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 7th International Conference of Materials Processing and Characterization.
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The coefficient of friction and wear of the composites decreases with increasing volume fraction of CNT content and wear properties are highly dependent on the method used for dispersion of CNTs in Aluminium matrix. AlQutub et al [4] found that wear and friction behavior of Al composites reinforced with CNTs are largely dependent on applied load and there exist a critical load beyond which CNTs have adverse impact on wear resistance of composites. Choi and coworkers [7] examined the wear mechanisms and mechanical properties of aluminium nano composites. It was found that MWCNTs form a strong interface with aluminium matrix by mechanical interlocking and wear resistance was significantly improved due to addition of CNTs and its decrease in grain size. The minimum wear loss was found to be 4.5 vol% of CNT and wear and coefficient of friction increased with increasing load but decreased with sliding speed. Niranjan and lakshinarayan [8] fabricated Aluminium matrix /titanium boride reinforced composite and tested its wear behavior using pin on disc wear testing machine. It was found that wear behavior of composite is significantly improved than unreinforced alloy. Oneida et al [9] tested the wear behavior of hybrid composite reinforced with carbon nanotubes and silica and found that there was increase in wear resistance and coefficient of friction was reduced. koji kato and koshi adachi [10] discussed the modes of wear of ceramics such as severe wear and mild wear. For severe wear, the wear debris is formed due to delamination of tribo films on the scale of grain size or mechanical cracking of grains. In case of mild wear, thin flakes are formed when detached from the soft and thin surface layer due to tribochemical reaction. The aim of the present study is to investigate the friction and wear properties of hybrid Al2024 composites reinforced with 10 wt% boron carbide particles and various MWCNT contents (1-2wt%). Test samples were obtained by stir casting with varying the wt% of reinforcements. Wear behavior of the samples were tested using 10N, 20N and 30N with sliding speed of 0.84m/sec against a steel disk of hardness Rc 60. 2. Experimental procedure 2.1 Materials Al 2024 with density 2.78 g/cm³, Young's Modulus of 73 GPa and begins to melt at 500 °C and has copper as the primary alloying element. Its application requires good fatigue resistance and high strength to weight ratio. Two different wt% of MWCNTs (1wt% and 2wt%) and fixed 10wt% of B4C are used in the experiment. Properties of reinforcements are shown in table 1 and 2. Table.1 Multiwalled carbon nanotube data sheet
MWCNT Production method Available form Diameter Diameter Length Nanotubes purity Metal particles Amorphous carbon Specific surface area Bulk density
Description Chemical vapour deposition Black powder Outer dia – 5-20nm Inner dia – 1-5 nm 10 micron >98% <1% <1% 330 m3g 0.20-0.35g/cm3
Table.2 Properties of boron carbide
Appearance density Melting point size
dark gray 2.52 g/cm3 2,763 °C 10-20 microns
Characterization method Proprietary method Visual TEM, SEM TEM, SEM TEM, SEM TGA, RAMAN TGA TGA/XRD BET PYCNOMETER
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Mohamed Zakaulla et al./ Materials Today: Proceedings 5 (2018) 5762–5767
The Al2024 alloy, which was in form of ingots was cut in to small pieces to accommodate in the graphical crucible. MWCNTs and B4C was mixed in a ball mill and then preheated at a temperature of 620°C. Al2024 was melted in a electric furnace and preheated reinforcements was added to molten metal at a temperature of 750°C and stirred continuously for 5mins at 450rpm. Finally the melt was poured in to a mould and allowed to solidify. 2.2 Wear test Friction and wear test of cast Al2024, Al2024/B4C and Al2024/B4C/MWCNTs hybrid composite is conducted using pin-on-disk type machine as per ASTM G99. Pins of height 30 mm and diameter 9 mm are served as specimens while hardened steel disc of Rc60 is used counter disc. Friction and wear test was carried out under dry sliding conditions at loads loads ranging from 10N to 30N at sliding speed of, 0.84m/sec. An 80mm fixed wear track diameter is used and loss of height of the samples is recorded by use of LVDT of accuracy of 1μm. Frictional force is continuously recorded using WINDCOM Software and Friction coefficient is found using the formulaμ = F/N where μ is the friction coefficient, F is the frictional force in Newtons, N is the Normal load in Newtons. 3. Results and discussion 3.1 specific wear rate
Fig 1 (a) Specific wear rate of Al2024 hybrid composite at 10N with 0.84m/sec
Fig 1 (b)Specific wear rate of Al2024 hybrid composite at 20N with 0.84m/sec
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Fig 1 (c)Specific wear rate of Al2024 hybrid composite at 30N with 0.84m/sec Figure 1 Specific wear rate of Al2024 hybrid composite at 0.84m/sec Fig 1 shows the specific wear rate of Al2024, Al2024/10%B4C, Al2024-10wt% B4C + 1%MWCNTs and Al202410wt% B4C + 2%MWCNTs composite. It is seen that dispersion of micro B4C particles in Al2024 matrix reduces the specific wear rate of Al2024/10%B4C composite in compare to Al2024 alloy. Decrease in specific wear rate is due to the presence of B4C particles which provides resistance to plastic deformation of Al2024 matrix when load is applied. Addition of multi walled carbon nanotubes with boron carbide particles enhances the wear resistance of hybrid Al2024 composite. Among them Al2024-10wt% B4C + 2%MWCNTs composite provides the best results since B4C particles and MWCNTs increases the hardness of composite and are uniformly distributed in the matrix and there is no agglomeration of MWCNTS in the Al2024 matrix as shown in above Fig 1 (a)(b) and (c). 3.2 coefficient of friction
Figure 2 coefficient of friction of Al2024 hybrid composite at 0.84m/sec
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Mohamed Zakaulla et al./ Materials Today: Proceedings 5 (2018) 5762–5767
It is observed from the fig 2 that Al2024 alloy experiences a higher coefficient of friction in compare to composites because it undergoes plastic deformation due to development of heat and friction at the sliding surface. The coefficient of friction of Al2024/10%B4C composite is more than Al2024-10wt% B4C + 1%MWCNTs and Al2024-10wt% B4C + 2%MWCNTs composite because of the self lubrication effect of multi walled carbon nanotubes which are dispersed in Al2024 matrix. Increase in content of multi walled carbon nanotubes decreases the Friction coefficient as it forms continuous lubricating film of carbon between the lower end of test piece and upper end of steel disk. 3.3 Characterization of worn surfaces
a)
c)
Al2024
Al2024-10wt% B4C + 1%MWCNTs
b) Al2024-10wt% B4C
d) Al2024-10wt% B4C + 2%MWCNTs
Figure 3 SEM images of Al2024 hybrid composite at 20N, 0.84m/sec and 1500m.
Mohamed Zakaulla et al./ Materials Today: Proceedings 5 (2018) 5762–5767
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Fig 3 shows the SEM images of Al2024 alloy Al2024 hybrid composites. It is in Fig 3 (a) (b) & (c) that the width of groove is more in sliding direction in Al2024 alloy in compare to composites. The Al2024/10% B4C /2%MWCNTs hybrid composite shows lesser voids, pits and grooves in compare to other composites because of the presence of high modulus and thermally stable MWCNTs and Boron carbide particles which increases hardness of composite and provide resistance to material flow during siding. Hence for Al2024-10wt% B4C + 2%MWCNTs and Al202410wt% B4C + 1%MWCNTs composites the plastic deformation of matrix is comparably lesser than Al2024/B4C composite and Al2024 alloy. 4. Conclusions Tribological behavior of Al2024 alloy, Al2024/10%B4C, Al2024-10wt% B4C + 1%MWCNTs and Al2024-10wt% B4C + 2%MWCNTs composite fabricated by stir casting technique was investigated under dry sliding condition using pin-on-disk machine under a constant sliding speed 0.84m/sec with different load of 10, 20 and 30N. The results showed that after incorporation of B4C particles and MWCNTs the wear resistance of hybrid Al2024 composite improved. The specific wear rate and coefficient of friction of Al2024-10wt% B4C + 2%MWCNTs composite under a load of 10, 20 and 30N with constant sliding speed 0.84m/sec was comparably lesser than Al2024 alloy, Al2024/10%B4C and Al2024-10wt% B4C + 1%MWCNTs composite. 5. References 1. S. R. Bakshi, D. Lahiri, and A. Agarwal, “Carbon nanotube reinforced metal matrix composites—a review,” International Materials Reviews, vol. 55, no. 1, 2010, pp. 41–64. 2. N. Silvestre, “State-of-the-art review on carbon nanotube reinforced metal matrix composites,” International Journal of Composite Materials, vol. 3, no. 6, 2013, pp. 28–44. 3. R. Casati and M. Vedani, “Metal matrix composites reinforced by nano-particles—a review,” Metals, vol. 4, no. 1,2014, pp. 65–83. 4. A. M. Al-Qutub, A. Khalil, N. Saheb, and A. S. Hakeem, “Wear and friction behavior of Al6061 alloy reinforced with carbon nanotubes,” Wear, vol. 297, no. 1-2, 2013, pp. 752–761. 5. C. R. Bradbury, J.-K. Gomon, L. Kollo, H. Kwon, and M. Leparoux, “Hardness of multi wall carbon nanotubes reinforced aluminium matrix composites,” Journal of Alloys and Compounds, vol. 585, 2014, pp. 362–367. 6. S.Zhou, X.Zhang, Z.Ding, C.Min, G.Xu, W.Zhu, Fabrication and tribological properties of carbon nanotubes reinforced Al composites prepared by presureless infiltration technique, composites part A: Applied science and manufacturing , 38, (2007), 301-306. 7. H.J.Choi, S.M.Lee, D.H.Bae, wear characteristics of aluminium based composites containing multiwalled carbon nanotubes, wear, 270, (2010), 12-18. 8. K. Niranjan and P. R. Lakshminarayanan, “Dry sliding wear behaviour of in-situ Al–TiB2 composites,” Materials and Design, vol. 47, 2013, pp. 167-73. 9. Oneida, Junko Umeda, Katsuyoshi Kondoh, Hisashi Imai,. Friction and wear behavior of sintered magnesium composite reinforced with CNTMg2Si/MgO, Materials Science and Engineering A 504, 2009, pp. 157–162.
10. K. Koji and A. Koshi, “Wear of advanced ceramics,” Wear, vol. 253(11-12), 2002,
pp. 1097-104.
ScienceDirect Materials Today: Proceedings 5 (2018) 5762–5767
www.materialstoday.com/proceedings
ICMPC 2017
Tribological Characteristics of Multiwalled Carbon Nanotubes And Boron Carbide Particles Reinforced Al2024 Matrix Composites Mohamed Zakaullaa, Arjun.Rb, Muzakkir Ahmed Khanc, Izhar Hussein Khand, Nadeem Pashae. a
H.K.B.K.C.E, Bangalore, 560045, India b U.V.C.E, Bangalore, 560068, India H.K.B.K.C.E, Bangalore, 560045, India d H.K.B.K.C.E, Bangalore, 560045, India e H.K.B.K.C.E, Bangalore, 560045, India c
Abstract Wear and friction behavior of Al2024 monolithic alloy reinforced with 10wt% B4C particles and MWCNTs varied in 1wt% and 2wt% was investigated. The hybrid Al2024 composite were fabricated using stir casting technique. Experiment was performed using pin-on-disk wear testing machine against a steel disk of hardness Rc 60 under a load of 10N, 20N and 30N with sliding speed of 0.84m/sec. The tribological test results indicated that Al2024-10wt% B4C + 2%MWCNTs displayed lower friction coefficient and wear rate compared to Al2024-10wt% B4C + 1%MWCNTs, Al2024-10wt% B4C composite and Al2024 alloy. The worn surfaces were examined using high resolution scanning electron microscope © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 7th International Conference of Materials Processing and Characterization. Keywords: wear; friction; boron carbide; sliding speed: sliding distance.
1. Introduction Aluminium composites reinforced with nanotubes and nanoparticles are currently used in fields such as electronics, transport, aerospace, renewable energy and architectural structure [1-3]. The combination of unique properties of carbon nanotubes and auminium alloys have great potential in weight sensitive applications [4-5]. Zhou and coworkers [6] fabricated aluminium composites reinforced with CNTs using pressure infiltration technique performed at 800°C in N2 atmosphere. They indicated that CNTs are well distributed and embedded in Al matrix. * Corresponding author. E-mail address : [email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 7th International Conference of Materials Processing and Characterization.
Mohamed Zakaulla et al./ Materials Today: Proceedings 5 (2018) 5762–5767
5763
The coefficient of friction and wear of the composites decreases with increasing volume fraction of CNT content and wear properties are highly dependent on the method used for dispersion of CNTs in Aluminium matrix. AlQutub et al [4] found that wear and friction behavior of Al composites reinforced with CNTs are largely dependent on applied load and there exist a critical load beyond which CNTs have adverse impact on wear resistance of composites. Choi and coworkers [7] examined the wear mechanisms and mechanical properties of aluminium nano composites. It was found that MWCNTs form a strong interface with aluminium matrix by mechanical interlocking and wear resistance was significantly improved due to addition of CNTs and its decrease in grain size. The minimum wear loss was found to be 4.5 vol% of CNT and wear and coefficient of friction increased with increasing load but decreased with sliding speed. Niranjan and lakshinarayan [8] fabricated Aluminium matrix /titanium boride reinforced composite and tested its wear behavior using pin on disc wear testing machine. It was found that wear behavior of composite is significantly improved than unreinforced alloy. Oneida et al [9] tested the wear behavior of hybrid composite reinforced with carbon nanotubes and silica and found that there was increase in wear resistance and coefficient of friction was reduced. koji kato and koshi adachi [10] discussed the modes of wear of ceramics such as severe wear and mild wear. For severe wear, the wear debris is formed due to delamination of tribo films on the scale of grain size or mechanical cracking of grains. In case of mild wear, thin flakes are formed when detached from the soft and thin surface layer due to tribochemical reaction. The aim of the present study is to investigate the friction and wear properties of hybrid Al2024 composites reinforced with 10 wt% boron carbide particles and various MWCNT contents (1-2wt%). Test samples were obtained by stir casting with varying the wt% of reinforcements. Wear behavior of the samples were tested using 10N, 20N and 30N with sliding speed of 0.84m/sec against a steel disk of hardness Rc 60. 2. Experimental procedure 2.1 Materials Al 2024 with density 2.78 g/cm³, Young's Modulus of 73 GPa and begins to melt at 500 °C and has copper as the primary alloying element. Its application requires good fatigue resistance and high strength to weight ratio. Two different wt% of MWCNTs (1wt% and 2wt%) and fixed 10wt% of B4C are used in the experiment. Properties of reinforcements are shown in table 1 and 2. Table.1 Multiwalled carbon nanotube data sheet
MWCNT Production method Available form Diameter Diameter Length Nanotubes purity Metal particles Amorphous carbon Specific surface area Bulk density
Description Chemical vapour deposition Black powder Outer dia – 5-20nm Inner dia – 1-5 nm 10 micron >98% <1% <1% 330 m3g 0.20-0.35g/cm3
Table.2 Properties of boron carbide
Appearance density Melting point size
dark gray 2.52 g/cm3 2,763 °C 10-20 microns
Characterization method Proprietary method Visual TEM, SEM TEM, SEM TEM, SEM TGA, RAMAN TGA TGA/XRD BET PYCNOMETER
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Mohamed Zakaulla et al./ Materials Today: Proceedings 5 (2018) 5762–5767
The Al2024 alloy, which was in form of ingots was cut in to small pieces to accommodate in the graphical crucible. MWCNTs and B4C was mixed in a ball mill and then preheated at a temperature of 620°C. Al2024 was melted in a electric furnace and preheated reinforcements was added to molten metal at a temperature of 750°C and stirred continuously for 5mins at 450rpm. Finally the melt was poured in to a mould and allowed to solidify. 2.2 Wear test Friction and wear test of cast Al2024, Al2024/B4C and Al2024/B4C/MWCNTs hybrid composite is conducted using pin-on-disk type machine as per ASTM G99. Pins of height 30 mm and diameter 9 mm are served as specimens while hardened steel disc of Rc60 is used counter disc. Friction and wear test was carried out under dry sliding conditions at loads loads ranging from 10N to 30N at sliding speed of, 0.84m/sec. An 80mm fixed wear track diameter is used and loss of height of the samples is recorded by use of LVDT of accuracy of 1μm. Frictional force is continuously recorded using WINDCOM Software and Friction coefficient is found using the formulaμ = F/N where μ is the friction coefficient, F is the frictional force in Newtons, N is the Normal load in Newtons. 3. Results and discussion 3.1 specific wear rate
Fig 1 (a) Specific wear rate of Al2024 hybrid composite at 10N with 0.84m/sec
Fig 1 (b)Specific wear rate of Al2024 hybrid composite at 20N with 0.84m/sec
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Fig 1 (c)Specific wear rate of Al2024 hybrid composite at 30N with 0.84m/sec Figure 1 Specific wear rate of Al2024 hybrid composite at 0.84m/sec Fig 1 shows the specific wear rate of Al2024, Al2024/10%B4C, Al2024-10wt% B4C + 1%MWCNTs and Al202410wt% B4C + 2%MWCNTs composite. It is seen that dispersion of micro B4C particles in Al2024 matrix reduces the specific wear rate of Al2024/10%B4C composite in compare to Al2024 alloy. Decrease in specific wear rate is due to the presence of B4C particles which provides resistance to plastic deformation of Al2024 matrix when load is applied. Addition of multi walled carbon nanotubes with boron carbide particles enhances the wear resistance of hybrid Al2024 composite. Among them Al2024-10wt% B4C + 2%MWCNTs composite provides the best results since B4C particles and MWCNTs increases the hardness of composite and are uniformly distributed in the matrix and there is no agglomeration of MWCNTS in the Al2024 matrix as shown in above Fig 1 (a)(b) and (c). 3.2 coefficient of friction
Figure 2 coefficient of friction of Al2024 hybrid composite at 0.84m/sec
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It is observed from the fig 2 that Al2024 alloy experiences a higher coefficient of friction in compare to composites because it undergoes plastic deformation due to development of heat and friction at the sliding surface. The coefficient of friction of Al2024/10%B4C composite is more than Al2024-10wt% B4C + 1%MWCNTs and Al2024-10wt% B4C + 2%MWCNTs composite because of the self lubrication effect of multi walled carbon nanotubes which are dispersed in Al2024 matrix. Increase in content of multi walled carbon nanotubes decreases the Friction coefficient as it forms continuous lubricating film of carbon between the lower end of test piece and upper end of steel disk. 3.3 Characterization of worn surfaces
a)
c)
Al2024
Al2024-10wt% B4C + 1%MWCNTs
b) Al2024-10wt% B4C
d) Al2024-10wt% B4C + 2%MWCNTs
Figure 3 SEM images of Al2024 hybrid composite at 20N, 0.84m/sec and 1500m.
Mohamed Zakaulla et al./ Materials Today: Proceedings 5 (2018) 5762–5767
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Fig 3 shows the SEM images of Al2024 alloy Al2024 hybrid composites. It is in Fig 3 (a) (b) & (c) that the width of groove is more in sliding direction in Al2024 alloy in compare to composites. The Al2024/10% B4C /2%MWCNTs hybrid composite shows lesser voids, pits and grooves in compare to other composites because of the presence of high modulus and thermally stable MWCNTs and Boron carbide particles which increases hardness of composite and provide resistance to material flow during siding. Hence for Al2024-10wt% B4C + 2%MWCNTs and Al202410wt% B4C + 1%MWCNTs composites the plastic deformation of matrix is comparably lesser than Al2024/B4C composite and Al2024 alloy. 4. Conclusions Tribological behavior of Al2024 alloy, Al2024/10%B4C, Al2024-10wt% B4C + 1%MWCNTs and Al2024-10wt% B4C + 2%MWCNTs composite fabricated by stir casting technique was investigated under dry sliding condition using pin-on-disk machine under a constant sliding speed 0.84m/sec with different load of 10, 20 and 30N. The results showed that after incorporation of B4C particles and MWCNTs the wear resistance of hybrid Al2024 composite improved. The specific wear rate and coefficient of friction of Al2024-10wt% B4C + 2%MWCNTs composite under a load of 10, 20 and 30N with constant sliding speed 0.84m/sec was comparably lesser than Al2024 alloy, Al2024/10%B4C and Al2024-10wt% B4C + 1%MWCNTs composite. 5. References 1. S. R. Bakshi, D. Lahiri, and A. Agarwal, “Carbon nanotube reinforced metal matrix composites—a review,” International Materials Reviews, vol. 55, no. 1, 2010, pp. 41–64. 2. N. Silvestre, “State-of-the-art review on carbon nanotube reinforced metal matrix composites,” International Journal of Composite Materials, vol. 3, no. 6, 2013, pp. 28–44. 3. R. Casati and M. Vedani, “Metal matrix composites reinforced by nano-particles—a review,” Metals, vol. 4, no. 1,2014, pp. 65–83. 4. A. M. Al-Qutub, A. Khalil, N. Saheb, and A. S. Hakeem, “Wear and friction behavior of Al6061 alloy reinforced with carbon nanotubes,” Wear, vol. 297, no. 1-2, 2013, pp. 752–761. 5. C. R. Bradbury, J.-K. Gomon, L. Kollo, H. Kwon, and M. Leparoux, “Hardness of multi wall carbon nanotubes reinforced aluminium matrix composites,” Journal of Alloys and Compounds, vol. 585, 2014, pp. 362–367. 6. S.Zhou, X.Zhang, Z.Ding, C.Min, G.Xu, W.Zhu, Fabrication and tribological properties of carbon nanotubes reinforced Al composites prepared by presureless infiltration technique, composites part A: Applied science and manufacturing , 38, (2007), 301-306. 7. H.J.Choi, S.M.Lee, D.H.Bae, wear characteristics of aluminium based composites containing multiwalled carbon nanotubes, wear, 270, (2010), 12-18. 8. K. Niranjan and P. R. Lakshminarayanan, “Dry sliding wear behaviour of in-situ Al–TiB2 composites,” Materials and Design, vol. 47, 2013, pp. 167-73. 9. Oneida, Junko Umeda, Katsuyoshi Kondoh, Hisashi Imai,. Friction and wear behavior of sintered magnesium composite reinforced with CNTMg2Si/MgO, Materials Science and Engineering A 504, 2009, pp. 157–162.
10. K. Koji and A. Koshi, “Wear of advanced ceramics,” Wear, vol. 253(11-12), 2002,
pp. 1097-104.