Preparation and Analysis of Silicon Carbide and Graphite Particulte Reinforcemtns in Aluminium...

8/18/2019 Preparation and Analysis of Silicon Carbide and Graphite Particulte Reinforcemtns in Aluminium Matrix

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ABSTRACT

Nowadays composite materials have become more popular for its wide range of applications and design flexibility. Since the fuel costs are increasing day to day, most of the automobile industries are conducting various experiments to develop composites having less densities and superior mechanical and tr

ibological properties which are equally cost effective. In view of these types of composites most of the research is focused on improving mechanical and tribological properties aluminium alloys by adding with ceramic reinforcements.

Silicon carbide is a compound of silicon and carbon with chemical formula SiC. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests.Graphite is well known for its self-lubricating properties, which is a semi metal and an allotrope of carbon.

Research was done to improve the properties of aluminium using both graphite and SiC as reinforcements on various alloys. This work mainly focuses on the Preparation and Analysis of Silicon Carbide & Graphite Particulate Reinforcemen

ts in Aluminium Matrix.

1. INTRODUCTION1.1. Composite MaterialA composite is when two or more different materials are combined together to create a superior and unique material.A composite material is made by combining two or more materials often ones thathave very different properties. The two materials work together to give the composite unique properties. However, within the composite you can easily tell thedifferent materials apart as they do not dissolve or blend into each other.1.1.1. Natural CompositesMany of us may not be noticed that several, naturally formed materials around us

are composites.Wood is a composite made from cellulose and lignin. The advanced forms of wood composites can be ply-woods. An excellent example of natural composite is muscles of human body. The muscles are present in a layered system consisting of fibers at different orientations and in different concentrations. These result in a very strong, efficient, versatile and adaptable structure. The muscles impart strength to bones and vice a versa. These two together form a structure that is unique. The bone itself is a composite structure. The bone contains mineral matrix material which binds the collagen fibres together.The other examples include: wings of a bird, fins of a fish, trees and grass. Aleaf of a tree is also an excellent example of composite structure. The veins in the leaf not only transport the food and water but also impart the strength to

the leaf so that the leaf remains stretched with maximum surface area. This helps the plant to extract more energy from sun during photo-synthesis (1).1.1.2. Man-Made CompositesThese composites are made by artificial mixing of two or more materials in definite proportions under controlled conditions. Mud mixed straw to produce stronger mud mortar and bricks, Plywood, Chipboards, Decorative laminates, Fibre Reinforced Plastic (FRP), Carbon Composites, Concrete and RCC, Reinforced Glass etc. The composites exist in day to day life applications as well. The most common existence is in the form of concrete. The concrete is a composite made from gravel,sand and cement. Further, when it is used along with steel to form structural components in construction, it forms one further form of composite.1.2. Why use composites?The biggest advantage of modern composite materials is that they are light as we

ll as strong. By choosing an appropriate combination of matrix and reinforcement material, a new material can be made that exactly meets the requirements of aparticular application. Composites also provide design flexibility because many


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ive reinforcement components. The flakes can be packed more densely when they are laid parallel, even denser than unidirectional fibres and spheres.Whiskers: These are nearly perfect single crystal fibres. These are short, discontinuous and polygonal in cross-section.1.5. Types of Composite Materials

There are two classification systems of composite materials. One of them is based on the matrix material and the second is based on the reinforcing mate

rial structure:1.5.1. Classification of Composites Based on Matrix Material

Since composite materials does not limit to any specific materials or metals, matrix can be any of the materials like plastics, glass, metals etc. all these materials were grouped based on the type of material. Figure 1.3 shows theclassification of composites based on the matrix materials. Figure 1.3 Classification of Composites Based on Matrix MaterialMetal Matrix Composites (MMC)

Metal Matrix Composites are composed of a metallic matrix (aluminium, magnesium, iron, cobalt, copper) and a dispersed ceramic (oxides, carbides) or metallic (lead, tungsten, molybdenum) phase.

Ceramic Matrix Composites (CMC)Ceramic Matrix Composites are composed of a ceramic matrix and embeddedfibers of other ceramic material (dispersed phase).Polymer Matrix Composites (PMC)

Polymer Matrix Composites are composed of a matrix from thermoset (Unsaturated Polyester, Epoxy) or thermoplastic (Polycarbonate, Polyvinylchloride, Nylon, Polystyrene) and embedded glass, carbon, steel or Kevlar fibers (dispersed phase).Carbon and Graphite

Carbon fibres in carbon matrix carbon/carbon composites used under extreme mechanical and thermal loads in space applications.1.5.2. Classification of Composites Based on Reinforcing Material

Reinforcing material in composites can be of different materials or the

combination of two or more materials (Hybrid Composites). One simple schema forthe classification of composites bases on reinforcing material is shown in Figure 1.4. Figure 1.4 Classification of Composites Based on ReinforcementsParticulate Composites

Particulate Composites consist of a matrix reinforced by a dispersed phase in form of particles.i. Composites with random orientation of particles.ii. Composites with preferred orientation of particles. Dispersed phase of these materials consists of two-dimensional flat platelets (flakes), laid parallel to each other.

Fibrous CompositesShort-fiber reinforced composites. Short-fiber reinforced composites consist ofa matrix reinforced by a dispersed phase in form of discontinuous fibers.i. Composites with random orientation of fibers.ii. Composites with preferred orientation of fibers.Long-fiber reinforced composites. Long-fiber reinforced composites consist of amatrix reinforced by a dispersed phase in form of continuous fibers.i. Unidirectional orientation of fibers.ii. Bidirectional orientation of fibers (woven).Structural Composites

Structural composites are combinations of composites and homogeneous materials. When a fiber reinforced composite consists of several layers with different fiber orientations, it is called multilayer (angle-ply) composite.

Composite Materials with Metal MatrixParticulate composites consist of particles immersed in matrices

such as alloys and ceramics. They are usually isotropic since the particles


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are added randomly. Particulate composites have advantages such as improvedstrength, increased operating temperature and oxidation resistance etc.Typical examples include use of aluminium particles in rubber, silicon carbide particles in aluminium, and gravel sand, cement to make concrete.

Flake composites consist of flat reinforcements of matrices. Typical flake materials are glass, mica, aluminium, and silver. Flake composites provide advantages such as high out-of plane flexural modulus, higher strength, and low co

st. Figure 1.5Composite Materials with Metal Matrices1.6. Manufacturing and forming methods of MMC

MMC manufacturing can be broken into three typessolid, liquid, and vapour.1.6.1. Liquid state methodsStir casting: Discontinuous reinforcement is stirred into molten metal, which is allowed to solidify.Electroplating and electroforming: A solution containing metal ions loaded withreinforcing particles is co-deposited forming a composite material.Squeeze casting: Molten metal is injected into a form with fibers pre-placed ins

ide it.Spray deposition: Molten metal is sprayed onto a continuous fiber substrate.Reactive processing: A chemical reaction occurs, with one of the reactants forming the matrix and the other the reinforcement.1.6.2. Solid state methodsPowder blending and consolidation (powder metallurgy): Powdered metal and discontinuous reinforcement are mixed and then bonded through a process of compaction, degassing, and thermo-mechanical treatment (possibly via hot isostatic pressing (HIP) or extrusion).Foil diffusion bonding: Layers of metal foil are sandwiched with long fibers, and then pressed through to form a matrix.1.6.3. Semi-solid state methodsSemi-solid powder processing: Powder mixture is heated up to semi-solid state an

d pressure is applied to form the composites.1.6.4. Vapour depositionPhysical vapour deposition: The fiber is passed through a thick cloud of vaporized metal, coating it.1.6.5. In situ fabrication technique

Controlled unidirectional solidification of a eutectic alloy can resultin a two-phase microstructure with one of the phases, present in lamellar or fiber form, distributed in the matrix.1.7. Stir Casting

Stir Casting is a liquid state method of composite materials fabrication, in which a discontinuous reinforcement is mixed with a molten matrix metal bymeans of mechanical stirring. The layout of conventional Stir Casting set up is

shown in Figure 1.6. Figure 1.6 Stir Casting Process

At first, the matrix metal is melted in the crucible and then metal treatment (like degassing, fluxing, etc.) is carried out without stirring. Later, stirrer is inserted into the crucible and allowed to rotate the molten metal. Vortex is formed in the crucible due to the rotation of stirrer. Required quantity of reinforcement is preheated in a separate chamber and is gradually added to the vortex for uniform mixing of reinforcement in to the matrix.

After the addition of reinforcement stirrer is removed from the crucible and the liquid composite material is then cast by conventional casting methodsand may also be processed by conventional Metal forming technologies.

2. LITERATURE REVIEW

In the last two decades, research has shifted from monolithic materials


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to composite materials to meet the global demand for light weight, high performance, environmental friendly, wear and corrosion resistant materials. Metal Matrix Composites (MMCs) are suitable for applications requiring combined strength, thermal conductivity, damping properties and low coefficient of thermal expansion with lower density. These properties of MMCs enhance their usage in automotiveand tribological applications (4). In the field of automobile, MMCs are used for pistons, brake drum and cylinder block because of better corrosion resistance a

nd wear resistance (5).There is a growing interest worldwide in manufacturing hybrid metal matr

ix composites [HMMCs] which possesses combined properties of its reinforcementsand exhibit improved physical, mechanical and tribological properties (6).

DiASil (Die Cast Aluminium Silicon) Cylinder, its application can be found on Yamaha R series bikes. A conventional cylinder has a steel sleeve, but the DiASil cylinder doesnt need a steel sleeve because it is made of abrasion-resistant aluminium alloy. The all-aluminium combustion chamber has a heat dissipation rate that is three times better than steel, which means great cooling performance. DiASil Cylinder adds a silicon content of 20% to the aluminium alloy to achieve the required hardness to resist abrasion (7). Honda Company used AMMC for cylinder liners in some of their engines like F20C, F22C and H22A (8).

According to Rohit Kumar, Ravi Rajan, & R K Tyagi, 2013 (9), the yield strengthand tensile strength of the composites decrease with increasing the volume fraction of the SiC particles, while the hardness of the composites increases with increasing the volume fraction of the SiC particles so that impact strength increases with increase in volume fraction of reinforcement at a certain limit (upto10 %) after starts decreasing.G.G. Sozhamannan, S. Balasivanandha Prabu and V. S. K. Venkatagalapathy 2012 (10) observed that production of Aluminium composite reinforced with discontinuousceramic particulates by Stir casting route will have homogeneous mix and is cost effective process. The major problem in this technology is to obtain sufficient wetting of particle by the liquid metal and to get a homogeneous dispersion ofthe ceramic particles.Neelima, Mahesh, & Selvaraj, 2011 (11) has conducted experiments on Al-SiC and s

howed that the weight tostrength ratio for Aluminium silicon carbide is about three times that of mild steel duringtensile test. Aluminium silicon carbide alloy composite material is two times less in weightthan the aluminium of the same dimensions. The maximum tensile strength has been obtainedat 15% SiC ratio. This indicates that the Aluminium silicon carbide composite material ishaving less weight and more strength.Dunia Abdul Saheb 2011 (12) compared the micro and macro structural behaviouralof Al-SiC and Al-Gr particulate composites by varing the weight fractions of SiC and Graphite. This study reveals that increasing trend of hardness with the increase in graphite up to 4 wt% weight fraction. Beyond this the hardness of composite decreases as graphite particles interact with each other leading to clustering of particles.

S. Naher, D. Brabazon and L. Looney 2003 (13) has simulated stir casting process using different blade designs and studied the effects of stirring speed, bladeangles and number of blades on the uniform dispersion of SiC particles into different liquid medium and time required for uniform dispersion of particles. Theynoticed the excessive vortex height is responsible for air entrapment into the liquid and is more in more viscous liquid. It was observed that settling times of particles only depends on the viscosity of the liquid metal and does not depend on the stirring speed and blade design.Elango, B.K.Raghunath, & K.Thamizhmaran (14) have conducted mechanical tests ona hybrid metal matrix composite with SiC and TiO2 on which the addition of SiC and TiO2 particulate significantly improves the yield strength and the ultimate tensile strength of LM25 alloy, when compared with that of unreinforced matrix. The ultimate tensile strength of Al LM25+SiC+TiO2 metal matrix composite when rei

nforced 15 vol. % is increased by 45.38%A.R Riahi and A.T Alpas 2001 (14) have focused on systemic tests of the role oftribo-layers which are formed on contact surfaces of hybrid composites with A356


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aluminium base. Tests were done on Al/SiC/Gr hybrid composite with A356 base, 10% SiC with particle size of 16 µm and 3% of graphite with particle size of 80 µm and 138 µm. Performed tribological tests determined dependence between wear and sliding speed and load. The tests were performed on block on ring tribometer for loads of 5420 N and for sliding speeds of 0.23.0 m/s.M.L. Ted Guo and C.Y.A. Tsao 2000 (15) have studied tribological behaviour of Al-SiC and graphite hybrid composites with different graphite composition and foun

d that friction coefficient decreases with the addition of graphite up to 5% and no considerable change noticed with further increase in graphite and also observed that hardness of the composite decreases with addition of graphite.B.MALLICK, P.C. MAITY and V.K. SINHA 1998 (16) explained that addition of magnesium to the liquid aluminium will reduce the surface tension of the melt facilitating the depression of ceramic particles in to the melt and also increases the wetting properties of metal-ceramic systems through reduction in solid-liquid interfacial energy.Basavaraju.S, November 2012 et al (18), studied the behaviour of graphite and fly ash by varying the percentage of Silicon Carbide and aluminum LM25 as base metal Prepared MMCs provide excellent wear characteristics up to a limit load. The tensile strength improves for 2% addition of SiC and 4% of SiC in Al+Graphite. Th

is proportion is ideal for many results to outcome easily. Similarly, 2% and 4%addition of SiC in Fly ash combination makes an efficient material. The hardness of the material increases with the combination of 2% addition of SiC and Graphite. The compressive strength is ideal at 2% and 4% addition of SiC graphite andFlyash.

Till now, significant work has been done on production of MMCs especially on producing light and durable composites using aluminium. Various works has been done for strengthening aluminium with reinforcements. In this regard, numberof researchers conducted experiments on aluminium composite with graphite and SiC reinforcements on various alloys. The present work will focus on fabrication mechanical properties of aluminium composite having LM16 as a matrix, SiC and graphite as reinforcements.

3. PROBLEMFORMULATION3.1. Identification of Need

Usage of automobiles was increasing day to day. But at the same time, search for alternate fuels increased as the conventional non-renewable sources ofpetroleum getting depleted. Simultaneously, automotive industries promoting thedevelopment of lighter and fuel efficient vehicles considering the manufacturing costs and the life of the vehicle.

Composite materials have more advantages over steel in automobile manufacturing. Composites are being considered to make lighter, safer and more fuel-efficient vehicles. Affordability is an important issue in vehicle manufacturing,which includes factoring in the costs associated with a cars complete life-cyclein

cluding manufacturing, operating and disposal costs.In view of developing less dense, low cost, highly durable materials for the automobile components, composites were the best choice for obtaining materials with such type of properties. Even though aluminium has replaced most of the ferrous based engine components like cylinder head, piston, cylinder block etc., its usage was restricted to very few applications due to very less wear resistance of aluminium alloys. This can be improved by pairing aluminium alloy with the materials having good tribological properties.3.2. Selection of Matrix

Aluminium is a relatively soft, durable, lightweight, ductile and malleable metal. Aluminium is remarkable for the metal's ability to resist corrosion due to the phenomenon of passivation. Aluminium has a lower density of 2.7 g/cc compared to 7.8 g/cc of steel. Aluminium alloys are lightweight with good corrosi

on resistance, ductility and strength. The greater use of aluminium can decrease vehicle weight, improve its performance and reduce fuel costs.

Pure aluminium possesses relatively poor casting features, for this reas


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on castings are prepared from aluminium alloys. The main alloying elements are silicon, copper, magnesium, zinc, etc. Aluminium silicon alloys have good casting and corrosion resistance properties. The fluidity increases with silicon addition. The addition of copper to aluminium increases its strength and hardness. The aluminium copper alloys are heat treatable and possess good machinability. Nowadays, aluminium alloys are replacing the ferrous alloys in manufacturing of automobile components.

Even though aluminium alloys have such remarkable properties, usage of aluminium is limited to some components because, compared to ferrous alloys aluminium alloys possess less hardness and wear resistance which can be improved by mixing suitable reinforcement.

Among various aluminium alloys LM16(Al Si5CulMg0.5) is one of the most popular aluminium alloy used for water-cooled cylinder heads, valve bodies, waterjackets, cylinder blocks, fire hose couplings, air compressor pistons, fuel pump bodies, aircraft supercharger covers and similar applications where leak-proofcastings having the high strength produced by heat-treatment are required.3.2.1. Chemical Composition of LM16 AlloyAccording to BS 1490; 1988 the chemical composition of LM16 alloy by weight is given below

Copper 1.0 - 1.5Magnesium 0.4 - 0.6Silicon 4.5 - 5.5Iron 0.6 maxManganese 0.5 maxNickel 0.25 maxZinc 0.1 maxLead 0.1 maxTin 0.05 maxTitanium 0.2 maxAluminium remainder3.2.2. Mechanical Properties of LM16 Alloy

According to BS 1490; 1988 the mechanical properties of LM16 alloy is as

belowTensile Stress (N/mm2) 270 - 280Impact Resistance Izod (Nm) 1.4Brinell Hardness 100 - 110Modulus of Elasticity (x103 N/mm2) 713.3. Selection of Reinforcements

Aluminium has very poor wear resistance compared to ferrous alloys. To improve the hardness and wear properties of aluminium alloy, reinforcement must possess relatively high hardness and wear resistance. Ceramics are the materialswhich stood in the top and well ahead of ferrous alloys. If a sound composite can be produced with ceramic reinforcement, then the composite may possess superior qualities equivalent or even better than some ferrous alloys.

In this regard, the reinforcement should also possess the chemical stability while mixing with aluminium. Materials having corrosion resistance, self-lubricating properties etc. will be an added advantage in this process.

Research has already been started to improve the tribological properties of aluminium alloy. Different experiments showed that the materials like SiC, graphite, granite, garnet etc. improved the hardness and wear properties of aluminium alloys (5) (17) (18) (15).

This work is mainly concentrated to develop a hybrid composite reinforced with both Silicon Carbide and graphite particulates.3.3.1. Silicon Carbide (SiC)

Silicon carbide is a compound of silicon and carbon with chemical formula SiC. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, s

uch as car brakes, car clutches and ceramic plates in bulletproof vests. The first use of SiC was as an abrasive. This was followed by electronic applications.SiC also has a very low coefficient of thermal expansion 4.0 × 10-6/K.


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SiC is used for its hardness in abrasive machining processes such as grinding, honing, water-jet cutting and sandblasting. Particles of silicon carbideare laminated to paper to create sandpapers and the grip tape on skateboards.3.3.2. Graphite

The mineral graphite is an allotrope of carbon. Unlike diamond (anothercarbon allotrope), graphite is an electrical conductor, a semimetal. It is, consequently, useful in such applications as arc lamp electrodes. Graphite is the mo

st stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carboncompounds. Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is difficult to ignite.

Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry lubricating properties. And hence, graphite may support SiC hardness by providing a layer self-lubrication between contact surfaces resulting in increase of wear resistance.3.4. Selection of Process

There are many advanced processes for producing metal matrix compositeswith discontinuous particulate reinforcement. Among all the processes, stir cast

ing route by producing vortex in the crucible by means of mechanical stirring is the most suitable and cost effective method for producing larger components with homogeneous mixture of metal-ceramic particulates (10), (16).

Most of the automobile components were produced by means of liquid metallurgy technique. This type of process is simple and cost effective technique ofproducing components. Stir casting is also one of the liquid metallurgy techniques for producing metal matrix composite.3.5. Selection of Optimal Composition

It is obvious that the properties of the final composite depend on the optimal composition of the SiC and Graphite. According to various studies conducted on Al-Gr MMCs, better properties were obtained up to 4% of Graphite in the Almatrix and the grain size of Graphite particulates varies from 40 to 150 microns based on process parameters.

It was observed that the conducted studies yields better properties of composite were obtained on 15% w/w Sic in Al matrix. In this regard, SiC rangingfrom 10% to 15% w/w will be sufficient for the present work. By comparing with similar ceramic particulates like SiC, Granite and alumina in various research works, the grain size of SiC particulates ranging from 50µm to 150µm may give better results.

Since a hybrid composite is going to be prepared, composition of reinforcements for obtaining better composite may differ from the results obtained from studies done with a single reinforcement. The resulting composite may show combined results of SiC and graphite. By studying Al-Graphite composites, it was observed that the graphite can be limited to 4% w/w and the SiC can be varied from10% to 15% w/w with a step of 5%.

4. EXPERIMENTALWORKConstruction of Stir Casting FurnaceFor the present work, it requires a stir casting furnace with 4 blade stainlesssteel stirrer. Since stir casting is not a conventional casting method, a suitable furnace has to be designed. Even though some stir casting furnaces are readily available in the market, a custom made conventional stir casting furnace is much cheaper and is best suited for the present work to vary process parameters according to the requirements.A conventional stir casting furnace consists of the following basic components.a. Furnaceb. Crucible

c. Stirring Equipment4.1.1. Preparation of Furnace

A furnace is prepared by using a cylindrical thick sheet metal drum. The


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inner wall of furnace is lined with refractory ceramic material to prevent heat losses and is sealed with glass wool material which is prepared form glass.

Fig. 4.5. FurnaceTotal furnace was made with kanthaal wire. It is applicable to produce heat up to 13500C. It is protected by 15mm thickness of ceramic material integrated with10% of iron.

Preparation of furnace body A furnace body is prepared by using different types of materials and sizes depend up on the requirement. Actual furnaces bodies are heavyweight and thick. In all types of furnaces body is the main thing, it holds the total set up except temperature controller. So it is very expensive and cost also. In this process preparation of body is low weight and low cost and expensive.It can withstands the high temperature depends on giving temperature. This typeof furnaces are easily to maintain, controllable and moving one place to another place is very easily, because it is low weight and convenient to moving. the specifications of the furnace body is discussed below. Figure 4.1 Preparation of furnace body

Temperature controllerA temperature controller is used to control the temperature of the furnace by the help of heat sensor.

Figure 4.2 Temperature controllerTemperature controllers are needed in any situation requiring a given temperature be kept stable. This can be in a situation where an object is required to be heated, cooled or both and to remain at the target temperature , regardless of the changing environment around it. There are two fundamental types of temperature control; open loop and closed loop control. Open loop is the most basic form and applies continuous heating/cooling with no regard for the actual temperature output. Closed loop control is far more sophisticated than open loop. In a closed loop application, the output temperature is constantly measured and adjusted to

maintain a constant output at the desired temperature. Closed loop control is always conscious of the output signal and will feed this back into the control process.4.1.2. Preparation of Stirrer

A 1200 rpm high torque reversible motor is taken and connected with a potentiometer for varying speeds as per the requirement. The motor shaft is coupled to a stainless steel rod and the other end is connected to a graphite three-blade impeller and is tested by stirring water in the crucible and grinded to thedesired angle for producing vortex. Figure 4.3 Stirrer SetupAssembly of stir casting

Stir Casting is a liquid state method of composite materials fabrication, in which a discontinuous reinforcement is mixed with a molten matrix metal bymeans of mechanical stirring. The layout of conventional Stir Casting. Figure 4.4 Stir Casting Process

At first, the matrix metal is melted in the crucible and then metal treatment (like degassing, fluxing, etc.) is carried out without stirring. Later, stirrer is inserted into the crucible and allowed to rotate the molten metal. Vortex is formed in the crucible due to the rotation of stirrer. Required quantity of reinforcement is preheated in a separate chamber and is gradually added to the vortex for uniform mixing of reinforcement in to the matrix.

After the addition of reinforcement stirrer is removed from the crucible

and the liquid composite material is then cast by conventional casting methodsand may also be processed by conventional Metal forming technologies.4.2. Consumables and Miscellaneous Materials


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A 15 litre silicon carbide crucible is bought for this purpose and is preheated to red hot condition (6500C) to relieve from internal stress. A stand is prepared for mounting of stirrer assembly above the furnace. To avoid vibrations in the stirrer, motor is mounted on springs which damp the vibrations. A ceramic cap is used to prevent motor from exposing to direct heat from the furnace. The stand is made as such that some small adjustments can be made to centre the stirrer to the crucible.

4.3. Procurement of Raw MaterialsAs the project is carried at SIBAR Auto Parts Limited, Aluminium alloy i

s provided from the companys inventory which was used for the production of engine cylinder heads. SiC and Graphite is purchased from a chemical shop in Chennaiand is also sieved for desired particle size.4.4. Sample Preparation

A standard test bar die (Permanent mould) is barrowed from Sibar Auto Parts Ltd. which will produce 27 mm diameter cylindrical rod with large riser on it to avoid shrinkage. It was tested that the test bar casting consumes 1 kg of molten metal.

Metal is melted in a separate furnace and is transferred to the stir casting furnace using a standard ladle which will carry 1.5 kg of molten aluminium.

The metal is maintained at 700oC temperature in the stir casting furnace. A sample is taken with no reinforcements directly before transferring to the stir casting furnace.

At first molten aluminium of weight 4 kg is taken in to the stir casting furnace. Graphite and SiC of 4% and 10% by weight is measured separately and simultaneously preheated in separate containers on the furnace itself. When the temperatures in the furnace were settled nearly above 700oC metal treatment is carried out by adding coverall to the molten metal which removes oxides and other impurities in the metal. Later, stirrer is inserted and allowed to rotate and create vortex in the crucible. The speed of the stirrer is controlled using potentiometer to get desired vortex. After the desired speed is maintained in the crucible reinforcements were added slowly to the vortex and after completely adding the reinforcements the stirrer is further allowed to rotate for ten more minutes

for uniform distribution of particulates.After stirring, molten metal from the crucible is poured into the die ca

vity using ladle and allowed to cure for about two minutes and removed from thedie. The remaining metal in the crucible is also used for taking the test samples. Same procedure is followed for producing samples of 4 % graphite and 15% SiC. All the samples were grouped and marked based on the composition of reinforcements and is sent to heat treatment process. Figure 4.5 Test Sample With Riser

All the samples were fully heat treated which includes solution heat treatment for 12 hours at 520-530oC and quenched in hot water followed by precipitation treatment of 8 hours at 170oC.

4.5. Experimental ProcedureAfter heat treatment of samples the following operations were performed.1. Specimens were analysed for variation in density as per Archimedes principle.2. Specimens were freed from risers and turned to required dimensions on alathe machine. Riser portions were shaped to rectangular sections and polished.3. Hardness test was conducted on the riser sections.4. Tensile test was conducted on turned samples with the help of Universaltesting machine. And average values of each composition were noted. 5. RESULTS AND DISCUSSIONS

After heat treatment of all samples, each sample was separately tested for the density, hardness and tensile strength and the average values were analys

ed by comparing with the zero sample. The results in various tests were discussed below.

For convenience of presentation and plotting, from here onwards pure LM-


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16 alloy samples were referred as Group 0, LM-16 with 4% Graphite and 10% SiC samples were referred as Group 1and LM-16 with 4% Graphite and 15% SiC samples were referred as Group 2.5.1. Density

Density of each sample was measured based on Archimedes principle in a calibrated glass jar. In Figure 5.1, it can be noticed that the density of composite is increased because of the increase of SiC composition.

Figure 5.1 Comparison of Density5.2. Hardness

Since the SiC is superior to aluminium and graphite in case of hardness, in general it can be expected that the dominance of SiC in increase of hardness of the composite. The practical observations revealed that the hardness of thecomposite increased considerably. It was noticed that the increase of hardness from Group 0 to Group 1 is form 108 BHN to 142 BHN has a difference of 34 BHN and the increase form Group 1 to Group 2 is from 142 BHN to 154 BHN has a difference of only 12 BHN (see Figure 5.2). This can be considered that the incorporation of SiC in the aluminium gives hardness to the composite but the further increase of SiC has given a little increase in hardness due to the domination of alumin

ium alloy over the composite since the composition of SiC is only 10% of weight. Further addition of graphite may give a considerable increase in hardness at some point but may affect interfacial strength and uniform distribution of reinforcement and also the other mechanical properties like density, tensile strength. Figure 5.2 Comparison of Hardness5.3. Tensile Strength

As it was the maximum stress that a material can withstand while being stretched, interfacial bonds may affect greatly on the tensile strength of the composite. In Figure 5.3, we can see that the tensile strength was increased in the composites but doesnt have comparable variation. Weak interfacial bonds may result in decrease in tensile strength of the composite, but here the increase of tensile strength shows that there was good interfacial strength. Since the reinfo

rcements were preheated before mixing with aluminium there might be uniform distribution and smooth interface while mixing. From this result we can expect goodinterfacial strength when we heat the reinforcements at higher temperatures which will facilitate uniform distribution of more amount of composite without losing the strength. Figure 5.3 Comparison of Tensile Strength5.4. Modulus of Elasticity

Modulus of elasticity shows linear relation with tensile strength as same as conventional materials. In Figure 5.4 we can observe that the modulus of elasticity was increased but not greatly as same as tensile strength. The elongation of material is similar to the base alloy, almost negligible amount of elongat

ion for all the groups. Since all the samples are fully heat treated, the samples will gain brittleness and hardness losing ductility which might be resulted in tendency of brittle failure. Figure 5.4 Comparison of Modulus of Elasticity

Even though no particular wear tests were performed on the samples, while removing the risers on a band saw cutting machine some resistance was observed on both the composite samples.5.5. Analysis of Composites using ANSYS 13.0

A pre modelled petrol engine cylinder is taken and is imported to ANSYSWORKBENCH. The model is meshed using a tetrahedral element and is subjected to boundary conditions i.e. forces, contacts, supports etc. The obtained results are imported to the material library and are applied to the model for obtaining the

results. Since the design of the cylinder is not changed, for the given gas pressure the stress developed in the cylinder will be same for all the compositions, only strain and deformation will change as per the material.


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Figure 5.5 3-Dimensional Petrol Engine Cylinder Model

Figure 5.6 Boundary Conditions and Constraints Defined to Model

Figure 5.7 Cylinder Model After Mesh Generation

Figure 5.8 Variation of Total Deformation for Group 0 (Pure Alloy) Figure 5.9 Variation of Strain for Group 0 (Pure Alloy)

Figure 5.10 Variation of Total Deformation for Group 1

Figure 5.11 Variation of Strain for Group 1

Figure 5.12 Variation of Total Deformation for Group 2

Figure 5.13 Variation of Strain for Group 25.5.1. Comparison of Total Deformation

It can be clearly observed in Figure 5.14 that for the given gas pressure the maximum total deformation of the cylinder model gets decreasing with increase of SiC in the composite. But the decrease of total deformation is not varying linearly. The slope of the curve from Group 0 to Group 1 is steeper than the curve from Group 1 to Group 2.

Figure 5.14 Comparison of Total Deformation5.5.2. Comparison of Strain

As the deformation is proportional to the strain, the maximum strain developed in the model seems similar to the comparison of total deformation. Figure 5.15 Comparison of Strain 6. CLOSURE6.1. Conclusion

From the experimental and analysis of present work the following conclusions are drawn.

1. Addition of SiC will increase the mechanical properties of the composite.2. By comparing with amount of SiC in the composite LM-16 with 4% graphiteand 15% SiC is most suitable for regular casting process.3. Hardness of the composite increased by 31.4% for 10% SiC and 42.5% for 15% SiC.4. It was noticed that the density of the composite is increasing with theincrease of silicon carbide.5. From the analysis the total deformation has been decreased by 6.9% for 10% SiC and 9.2% for 15% SiC. So, it can be concluded that this composite material in engine cylinders can be used for higher capacities than that of which theyare now using.

6.2. Scope of Future Work1. Wear analysis can be done on the same composition to find the wear properties and lubrication effect of graphite in the composite.


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2. Since SiC has very low thermal expansion and an insulator, thermal properties of the composite can be studied for using at higher temperatures.3. Microstructure analysis can be performed to study the interfacial strengths and uniform distribution of particulates.4. More composites with higher SiC and graphite percentage can be preparedby employing some modifiers and changing process parameters which might result in better properties.

5. Other self-lubricants like boron nitride can be used in place of graphite which will further increase wear resistance and hardness.

Preparation and Analysis of Silicon Carbide and Graphite Particulte Reinforcemtns in Aluminium...

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