I.INTRODUCTION. II.CNT-Al NANO-COMPOSITE

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1 International Journal of Advances in Engineering, 2015, 1(3), ISSN: (printed version); ISSN: (online version); url: RESEARCH ARTICLE Development of Al-CNT Composite by Powder Metallurgy Method Dr. M. Arockia Jaswin, A.Vijayasekar, P.Purushothaman, S.Ramu, M.Sugumar Department of Mechanical Engineering, Aksheyaa College of Engineering, India Received 19 February 2015 / Accepted 10 March 2015 Abstract--In recent years, carbon nanotubes (CNTs) reinforced aluminum composites (AL) have increasing attention. Carbon nanotubes can be considered as ideal reinforcements, due to their high strength, high aspect ratio and thermomechanic properties. Powder metallurgy techniques have emerged as promising routes for the fabrication of carbon nanotubes (CNT) reinforced metal matrix composite. In this project, powder metallurgy processing approach has been undertaken to fabricate a CNTs-AL nano-structural composite. Key words Carbon nanotubes, Aluminium powder, powder metallurgy technique. I.INTRODUCTION Nanotechnology may be able to create many new materials and devices with a vast range of applications, such as in medicine, electronics, biomaterials and energy production aviation departments and automotive sectors. The interest in carbon nanotubes (CNTs) as super reinforcements for metallic matrices has been growing considerably over the past few years, largely focusing on investigating their contribution to the enhancement of the mechanical performance of the final composite. Carbon nanotubes (CNTs) are near ideal whiskers. Consisting of seamless cylinders formed by rolling a grapheme sheet, and exhibit many remarkable mechanical, electrical and thermal properties. Carbon nanotubes are very attractive to researchers and scientists in view of their extraordinary physical properties and exceptional potential of practical applications. In addition to remarkable chemical and thermal stability, single-walled carbon nanotubes (SWNT) has a very high Young s modulus (up to 5TPa)[1]which is much higher than that of the best known steel (up to 150GPa)[2]. Although multi-walled carbon nanotubes (MWNT) shows lower mechanical properties (Young s modulus is up to 1.8 TPa) than SWNT[7], experimental and theoretical results prove that MWNT[3] is more chemically stable which along with low massive produce prices make MWNT more widely industry applicable. In order to achieve the full potential of carbon nanotubes reinforced metal matrix. A very limited research has been done in the field of CNTs reinforced Al matrix composites because of the complexity associated with theinterfacialreaction between CNTs and Al matrices, and lack of a suitable synthesis technique. Powder metallurgy techniques have emerged as promising routes for the fabrication of carbon nanotubes (CNT) reinforced metal matrix composites. The result showed that powder metallurgy is the simpler and cheaper way of making aluminum nano-composite with uniform Dispersion of CNTs and improved mechanical, wear and frictional properties. In this work, planetary ball milling was used to disperse 1wt% MWCNT in aluminum (Al) powder. One way to produce composites with uniform distribution of CNTs within the metallic matrix is by first dispersing them in metal powders then subsequently consolidating these Al CNT composite powders. The ball-milling process, although effective, normally results in strain hardening of the powders, and this can have implications on the final properties of the bulk composite. In powder metallurgy technique, powder mixing process is conducted by ball milling process. There are two type of ball milling process one is high ball milling another one is low ball milling. This paper discussed the high ball milling. In previous studies by the authors, dispersion of 2 and 5 wt% CNTs in aluminum powders was achieved, and the effect of milling time on the morphological evolution of the Al CNT composite powders was investigated. This paper discussesthe consolidation of Al CNT composite powders using ball milling with 1wt% CNTs. II.CNT-Al NANO-COMPOSITE Al is a soft gray color, ductile and malleable metal that is abundant in the earth s crust. It is impossible to keep it in its pure form without chemical reactions; when exposed to air it directly forms an oxide layer on the surface which will act as a protective shield from further oxidation. It has a relatively low density compared to other metals which makes it one of the best choices for manufacturing components used in light weight applications. Various types of Al matrix composites have been developed and extensively in use over the past decades in aerospace and automotive industries (Farahani 2010). Reinforcing aluminum with minimum percentage of carbon nanotubes (CNT) using powder metallurgy processing route for the development of lighter weight nano-composite will improve the homogeneity, reduce the susceptibility to oxidation, enhance the strength and stiffness, wear resistance, stable friction co-efficient, density and coefficient of thermal expansion. Therefore, this will attract the lightweight industries, such as aerospace, automotive and other industries to use nano-composite material for tribological applications. Research has

2 363 Int. J. Adv. Eng., 2015, 1(3), been done by Cho et al. (2011) using copper as a matrix and CNT as reinforcement and achieved increased mechanical properties of the composite material compared to matrix material. Liao et al. (2011) conducted a study on the CNT dispersion in Al powder by different mixing techniques, i.e. (i) high energy ball milling, (ii) low energy ball milling and (iii) a polyester binder-assisted (PBA) approach. Zare et al. (2012) achieved uniform distribution of CNTs without agglomeration in aluminum powder using ultrasonic and ball mill attrition. The main features of CNT-Al composites are: lower density, high heat dissipation properties, stable friction coefficient, dimensional stability and better wear resistance the surrounding components in the brake system. These properties can fulfill of many structural and tribological components and hence can be considered for automotive and aerospace applications. III.EXPERIMENTATION The starting materials in this study consisted of Al powder and MWCNTs with specification as follow: Al powder (purity 99%, 200 mesh 45micron), MWCNTs from (www. cheapertube.com) purity >95% (OD diameter nm, ID diameter nm, length 1 2 μm, special surface area m2/g). Powder Metallurgy Route : Powder metallurgy is the name given to the process by which fine powdered materials are mixed, pressed into a desired shape, and then heated to bond surfaces. Powder metallurgy (PM) is considered to be the most common and cheaper production route for composite fabrication and characterized by good dimensional and geometrical precision as well as good mechanical properties. Figure.1 Carbon nanotubes aluminium nanocomposite Using PM process, several properties of Nano-composite can be improved such as hardness, wearresistance, mechanical durability, thermal durability, and thermal conductivity with decreased density of the material. With this improvement in Nano-composite properties, the material exhibited better quality and can be used in many applications whereby demand of quality and less cost material are high especially in automotive and aerospace applications.powder metallurgy route can be sub divided in to four different methods depending on type of pressure and heat. Fig.1 shows subdivisions of PM route which can be employed for CNT-Al fabrication purposes.the basic overall process steps consist of mixing of CNTs with aluminium powder by grinding or mechanical alloying, followed by compaction consolidation and sintering, cold isostatic pressing, hot isostatic pressing, or spark plasma sintering. The deposition of CNTs on to aluminium powder by pressure and heat process. A. High energy ball milling Al- CNT powders were mixed by stirring before being transferred into the ball milled jar. Mechanical alloying was performed on a Retch PM400, Indian planetary ball mill machine. To prevent severe cold rolling, stearic acid (1 wt %) was added to the mixture during the ball milling. Ball to powder weight ratio was 5:1 with a revolution speed of 400 RPM. Ball milling time was 4 h, with an interim period of 25 min for every one hour, in order to prevent over-heating. B. Low energy ball milling The same amount of Al-CNTs powders and balls as used in high energy ball milling were loaded into a plastic container then blended by a horizontal rolling machine. The mixture was rolled for 2 h continuously with a speed of 200 rpm.

3 363 Int. J. Adv. Eng., 2015, 1(3), C. Polyester binder-assisted (PBA) mixing A polyester binder assisted (PBA) method for coating CNTs on Al powder was used. Firstly, polyethylene glycol (PEG) with a molecular weight of 20,000 (MW. 20,000) in a form of flake was hand mixed with CNTs in a mortar. The mixture was transferred into a Haake twin screw mixer. To effectively disperse the CNTs within the PEG, the mixture was melt blended for 20 min, at the desired melting point of PEG, i.e. 70 C, using a speed of 60 rpm. III. Al-CNTs COMPOSITE FABRICATION TECHNIQUES A. Mixing Progress For Al-CNTs composite low energy ball milling is suitable method for fabrication. The basic overall process steps consist of mixing of CNTs with aluminum powder by grinding or mechanical alloying, followed by compaction consolidation and sintering, cold isostatic pressing, hot isostatic pressing, or spark plasma sintering. The deposition of CNTs on to aluminum powder by pressure and heat process. 10gramsofAl(99.7%,pure200mesh 45micron.) and 1wt% multi-wall carbon nanotubes were placed in 250ml stainless steel mixing jars together with 75 stainless steel milling balls (10mm diameter); giving a ball-to-powder weight ratio of 5:1.The jars were filled with argon and were agitated using a ball mill at 200 rpm for 2h. 3ml of ethanol were added as a process control agent (PCA) in order to minimize cold welding of the Al particles and also to prevent powders sticking to the balls and the jar wall. B. Compacting Blended powers are pressed in dies under high pressure to form them into the required shape. The work part after compaction is called a green compact or simply a green, the word green meaning not yet fully processed. The conventional compaction method is pressing, in which opposing punches squeeze the powders contained in a die. The work part after pressing is called a green compact. Powders do not flow like liquid, they simply compress until an equal and opposing force is created. When the pressure is applied by only one applied by only one punch, the maximum density occurs right below the punch surface and decreases away from the punch. This method is widely used to fabricate CNT/MMC composite. Esawiet al. (2008), used a powder rollingtechnique to fabricate carbon nanotubereinforced aluminium strips. The CNT-Al mixtures are blended in a mixer-shaker at a rotary speed of 46rpm, and under argon gas in a planetary mill at a rotary speed of 300rpm, prior to rolling. However, the dispersion of the nanotubes was found to be better under the higher energy planetary action. The strength of the rolled strips is evaluated for various wt% of CNT nano-composite samples. The 0.5 wt% CNT-Al composite strips exhibited enhanced mechanical properties. The CNT- reinforced aluminium strips can have numerous attractive applications in the aerospace, automotive and electronics industries. Liao et al. (2011) conducted a study on the CNT dispersion in Al powder by different mixing techniques, i.e. (i) high energy ball milling, (ii) low energy ball milling and (iii) a polyester binderassisted (PBA) approach. The study revealed that using the high energy ball-milled CNTs were well dispersed, though not sufficiently distributed within the Al powder because of the gravity separation (density difference). This high energy ball milled CNTs were disintegrated due to residual stresses in the CNTs. The polyester binder assisted CNTs were coated on the surface of Al powder. The greatest advantage of PBA method lied in the maintenance of the CNTs structure and morphology in its original form. As a comparison, the low energy ball milled shows moderate damage. The results of mechanical properties revealed that the powder mixing was successful. Small addition of CNTs (0.5 wt.%) could enhanced the strength and hardness of the composite compared with the pure aluminium matrix. C. Compacted and uncompact Composite (a) (b) Figure. 2 a) Carbon nano particle powder b) Aluminium powder

4 364 Int. J. Adv. Eng., 2015, 1(3), Figure.3 Al-CNT compacted For Al-CNTs composite one gram of ball milled powder is poured into the die to produce 10 mm diameter with 4-5mm thickness by using motorized hydraulic press is used in 2.5 ton load is applied. Now the green compact is produced. Figure.4 Green compact Sintering Compressed metal powder is heated in a controlled-atmosphere furnace to a temperature below its melting point, but high enough to allow bounding of the particles Sintering is the process by which metal powder compacts (or loose metal powders) are transformed into coherent solids at temperatures below their melting point. Sintering is the heating to a temperature below the melting point to cause solid state bonding of particles. Heat treatment to bond the metallic particles, thereby increasing strength and hardness. Usually carried out at between 70% and 90% of the metal's melting point (absolute scale). Generally agreed among researchers that the primary driving force for sintering is reduction of surface energy. Part shrinkage occurs during sintering due to pore size reduction. During sintering, the powder particles are bonded together by diffusion and other atomic transport mechanisms, and the resulting somewhat porous body acquires a certain mechanical strength.sintering process are done by below the melting point of the main powder (aluminum).for Al-CNTs composite sintering temperature is between 500 C -550 C. By sintering the property of the composite is emerged change. When a powder compact is heated in a protective atmosphere to a temperature below the melting point of the major component, a densification of the powder occurs by eliminating pores and a sintered product of increased mechanical strength is formed. On a microscopic scale, cohesion takes place as necks form and grow at the points of particle contact. The sintering temperature is typically around 600 C. The driving force for sintering is the reduction in surface energy of the powder and is rather small. To increase this driving force, sintering can be carried out with the addition of reactive elements or with additional components that become liquid at the sintering temperature

5 365 Int. J. Adv. Eng., 2015, 1(3), (liquid phase sintering). Another alternative is to apply an external pressure during sintering (pressure sintering). The efficiency of a sintering process is mainly influenced by the temperature, the time, the properties of the protective atmosphere, the density of the compact, the particle size and the particle shape. Figure.5 (1) blendig and mixing powders, (2)compacting, (3)sintering Figure.6 1. Particle bonding is initiated at contact points; 2. Contact points grow into "necks"; 3. pores between particles are reduced in size; 4. grain boundaries develop between particles in place of necked regions Figure.7 (a) SEM image of carbon nanotubes (b) TEM image of carbon nanotubes CONCLUSION In the area of fabrication of CNT-Al nano-composite, PM is the most cost effective and captive process. Therefore, this PM process route with appropriate processing technique factors can help to develop a new nano-composite material without sacrificing any functional properties and hence, the lightweight industries, such as aerospace, automotive, sports and other industries will be attracted to use this material for many structural and tribological applications. Carbon nanotubes (CNTs) reinforced aluminum composites (AL) have increasing attention. Carbon nanotubes can be considered as ideal reinforcements, due to their high strength, high aspect ratio and thermo- mechanic properties.

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