CHAPTER 1

INTRODUCTION

1.1 COMPOSITE

Composite material is a material composed of two or more distinct phase (matrix phase and reinforcing phase) and having bulk properties significantly different from those of any of the constituents. Composite materials (also called composition materials or shortened to composites) are materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. The new material may be preferred for many reasons: common examples include materials which are stronger, lighter or less expensive when compared to traditional materials. Many common materials (metals, alloys, doped ceramics and polymers mixed with additives) also have a small amount of dispersed phase in their structures ,however they are not considered as composite materials since their properties are similar to those of their base constituents (physical property of steel are similar to those of pure iron). Favorable properties of composites materials are high stiffness and high strength, low density, high temperature stability, high electrical and thermal conductivity, adjustable coefficient of thermal expansion, corrosion resistance, improved wear resistance etc.

1.1.1 Need for Composites

The biggest advantage of modern composite materials is that they are light as well as strong. By choosing an appropriate combination of matrix and reinforcement material, a new material can be made that exactly meets the requirements of a particular application. Composites also provide design flexibility because many of them can be moulded into complex shapes. The downside is often the cost. Although the resulting product is more efficient, the raw materials are often expensive. Some of the most important points are listed below. To increase the yield strength and tensile strength at room temperature and above while maintaining the minimum ductility or rather toughness.

To increase the fatigue strength at high temperature. To increase the creep resistance at high temperature. To improve the thermal shock resistance.

To improve the corrosion resistance.

1.1.2 Composition of Composites

Composite mainly consists of two major phases.

Matrix phase

The primary phase, having a continuous character.

Usually more ductile and less hard phase.

Holds the reinforcing phase and shares a load with it. Provides the bulk form of the part or product made of the composite material. Holds the imbedded phase in place, usually enclosing and often concealing it. When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent.

Reinforcing Phase

Second phase (or phases) is embedded in the matrix in a discontinuousform. Usually stronger than the matrix. Function is to reinforce the primary phase Imbedded phase is most commonly one of the following shapes:1. Fibers2. Particles3. Flakes In addition, the secondary phase can take the form of an infiltrated phase in a skeletal or porous matrix.

1.1.3 Characteristics of Composites

Composites as engineering materials normally refer to the material with the following characteristics: These are artificially made (thus, excluding natural material such as wood).

These consist of at least two different species with a well defined interface.

Their properties are influenced by the volume percentage of ingredients.

These have at least one property not possessed by the individual constituents.

1.1.4 Factors Affecting Performance of Composite

1. Properties of matrix and reinforcement.

2. Size and distribution of constituents.

3. Shape of constituents

4. Nature of interface between constituents.

1.1.5 Classification of Composites

Composite materials are classified

On the basis of matrix material. On the basis of filler material.

A. On the Basis of Matrix

1. Metal 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.Metal matrix composites, at present though generating a wide interest in research fraternity, are not as widely in use as their plastic counterparts. High strength, fracture toughness and stiffness are offered by metal matrices than those offered by their polymer counterparts. They can withstand elevated temperature in corrosive environment than polymer composites. Most metals and alloys could be used as matrices and they require reinforcement materials which need to be stable over a range of temperature and non-reactive too. However the guiding aspect for the choice depends essentially on the matrix material. Light metals form the matrix for temperature application and the reinforcements in addition to the aforementioned reasons are characterized by high moduli.Most metals and alloys make good matrices. However, practically, the choices for low temperature applications are not many. Only light metals are responsive, with their low density proving an advantage. Titanium, Aluminium and magnesium are the popular matrix metals currently in vogue, which are particularly useful for aircraft applications. If metallic matrix materials have to offer high strength, they require high modulus reinforcements. The strength-to-weight ratios of resulting composites can be higher than most alloys.The melting point, phyNano SiCal and mechanical properties of the composite at various temperatures determine the service temperature of composites. Most metals, ceramics and compounds can be used with matrices of low melting point alloys. The choice of reinforcements becomes more stunted with increase in the melting temperature of matrix materials.

2. Ceramic Matrix composites (CMC)

Ceramic Matrix composites are composed of a ceramic matrix and imbedded fibres of other ceramic material (dispersed phase).Ceramics can be described as solid materials which exhibit very strong ionic bonding in general and in few cases covalent bonding. High melting points, good corrosion resistance, stability at elevated temperatures and high compressive strength, render ceramic-based matrix materials a favourite for applications requiring a structural material that doesnt give way at temperatures above 1500C. Naturally, ceramic matrices are the obvious choice for high temperature applications.High modulus of elasticity and low tensile strain, which most ceramics possess, has combined to cause the failure of attempts to add reinforcements to obtain strength improvement. This is because at the stress levels at which ceramics rupture, there is insufficient elongation of the matrix which keeps composite from transferring an effective quantum of load to the reinforcement and the composite may fail unless the percentage of fiber volume is high enough. A material is reinforcement to utilize the higher tensile strength of the fiber, to produce an increase in load bearing capacity of the matrix. Addition of high-strength fiber to a weaker ceramic has not always been successful and often the resultant composite has proved to be weaker.

3. Polymer Matrix Composites (PMC)

Polymers make ideal materials as they can be processed easily, possess lightweight, and desirable mechanical properties. It follows, therefore, that high temperature resins are extensively used in aeronautical applications.Two main kinds of polymers are thermosets and thermoplastics. Thermosets have qualities such as a well-bonded three-dimensional molecular structure after curing. They decompose instead of melting on hardening. Merely changing the basic composition of the resin is enough to alter the conditions suitably for curing and determine its other characteristics. They can be retained in a partially cured condition too over prolonged periods of time, rendering Thermosets very flexible. Thus, they are most suited as matrix bases for advanced conditions fiber reinforced composites. Thermosets find wide ranging applications in the chopped fiber composites form particularly when a premixed or moulding compound with fibers of specific quality and aspect ratio happens to be starting material as in epoxy, polymer and phenolic polyamide resins.

B. On the basis of Material1. Particulate compositesParticulate composites consist of a matrix reinforced by a dispersed phase in form of particles. Composites with random orientation of particles.

Composites with preferred orientation of particles.

2. Fibrous Composites

I. Short-fibre reinforced composites:

Short-fibre reinforced composites consist of a matrix reinforced by dispersed phase in form of discontinuous fibres.

II. Long-fibre reinforced composites:

Long-fibre reinforced composites consist of a matrix reinforced by a dispersed phase in form of continuous fibres.

1.2 NANOTECHNOLOGY

Nanotechnology applications are a reality today. American car manufacturers have been using nanotubes to improve the safety of fuel-lines in passenger vehicles for over a decade, and the electronics industry has been relying on nanotubes in its packaging material to better protect goods and to aid the removal of any electrical charges before they can build to disruptive levels. Nanotechnology is one of the very frontiers of science today. As a matter of fact, nanotechnology could affect us all, beyond nanoparticles, critical length scales and nano tools: so, European citizens should be able to see how all this science and technology could influence their lives ahead of the actual developments. Beyond any spontaneous enthusiasm or mistrust any such highly innovative scientific development may bring, the fact that nanotechnology is becoming more and more deeply embedded in todays life should warrant a meaningful, conscientious communication based on a continuous participation and exchange between stakeholders and citizens. Japan, korea, Taiwan, and European countries including Scotland and the Netherlands have also played influential roles in the development of nanotechnology capabilities and the technology continues to be of world-wide interest.The potential for more broad based nanotechnology applications will come from a better understanding of how particles operate on a nano scale and how biological and non-biological particles can be integrated-research and development continues in these fields and many others. There is still a way to go before we fully understand the workings and potential applications of the assembly of atoms and how to make these processes scalable, profitable and standardized.

1.2.1 Potential Benefits of nanotechnology

There are many examples of possible applications of nanotechnology developments. These include new materials, new medical, pharmaceutical, agricultural and environmental processes and devices; new electronic devices, new sensors, and new computing paradigms. The ability to exploit the atomic and molecular properties of materials allows the development of a variety of new functions for current products. The nanometre scale is conventionally defined as 1 to 100 nm. One nanometre is one billionth of a metre (10-9 m). The size range is normally set to a minimum of 1 nm to avoid single atoms or verysmall groups of atoms being designated as nano-objects. Therefore, nanoscience and nanotechnologies deal with clusters of atoms of 1 nm in at least one dimension.It is not unfeasible to develop paints that repair themselves when chipped, or for computers the size of blood cells with tiny wireless transmitters to report on the health of a patient without requiring surgery, or for nano-scale cleaning particles to identify and fight contaminants in our waterways not unfeasible but also not in the near term. But it is exactly this far-reaching potential of nanotechnology that is now making it one of the most important areas of science and one of the most important areas of science and one of the most commercially exciting.

1.3 NANO PARTICLES

Nano particles possess unique hybrid properties of neither the molecular nor the bulk solid-state limits. Nano particles processing offers a practical way to tailor the properties at the atomic or molecular level, producing novel materials with a unique size dependent behaviour such as quantum size effect and greater micro-structural uniformity. Metal nanoparticles are a clear example of how the properties of matter can change at the nanometer scale. For instance, metal gold is notably yellow in colour and used for jewellery. As the noblest of all metals, gold is very stable (e.g. it does not react with oxygen or sulphur). However, if gold is shrunk to a nanoparticle, it changes colour, becoming red if it is spherical and even colourless fit is shaped in a ring. Moreover, gold nanoparticles become very reactive and can be used as new catalysts. The advancement of technology at different levels as improved the manufacturing of materials with improved and definite characteristics. Hence the traditional materials are high competition with advanced materials. Ceramics, composites and polymeric materials claim to provide lighter weight, greater strength and overall better electrical, thermal and optical properties than the conventional materials. The recent technology focuses mainly on the size of the particles in the order of nano meters. Nano particles may be defined as those particles having dimensions in the range 1 to 100nm.It is realized that the nano particles have high surface to volume ratio, the baNano SiC factor that has improved the material performance in general. The volume of an object decreases as the third power of its linear dimensions, but the surface area only decreases as its second power. Materials scientist are challenged to identify build, control and test the structures whose dimensions are in nano meter scale and to demonstrate the potentials of these nanostructures in scientific, industrial applications while keeping in mind their potential impact on society. In general the nano particles are larger than individual atoms and molecules but are smaller than bulk solid. Hence they obey neither absolute quantum chemistry nor loss of classicals, physicals and have properties that differ markedly from those expected.Nano particles offer a practical way of retaining the results of the property at the atomic or molecular level, producing novel materials with unique size-dependent behaviour including quantum confinement effects, super magnet and good micro structural uniformity. The unique phenomenon that occurs in nano particles allows their properties (electrical, optical, chemical, mechanical, magnetic etc.) to be tailored selectively by varying the size, morphology and composition of particles. These new substance will have enhanced or entirely different properties from their parent materials.Nano clusters have at least one dimension between 1 to 10 nano meters and a narrow sized distribution. Nano powders are agglomerates of ultrafine particles, nano particles or nano clusters. Nano meter sized single crystals or single-domain ultrafine particles are often referred to as nanocrystals. Nano particle research is currently an area of intense scientific research, due to a wide variety of potential applications in biomedical, optical and electronic field.

1.4 PROPERTIES OF NANOPARTICLES

The general phyNano SiCal and chemical properties of nano size particles are1 High Density

2 Low thermal conductivity

3 Chemical inertness

4 Resistance to molten metals

5 Ionic electrical conduction

6 Wear resistance

7 High fracture toughness 1.5 SYNTHESIS OF NANOPARTICLES

There are two ways of synthesizing the nano particles.

i. Physical methods

ii. Chemical methods

1.5.1 Physical Methods

i. Evaporation and condensation method

ii. Plasma heating method

iii. Co2 laser method

iv. Mechanical alloy method

v. Pulsed wire evaporation method

1.5.2 Chemical Methods

i. Chemical vapour deposition method

ii. Liquid phase reduction method

iii. Hydro-thermal synthesis

iv. Sol-gel method

1.6 Classification of Composite Materials by Matrix Material

Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, such as cemented carbides and other cermets. Ceramic Matrix Composites (CMCs) - Al2O3 and Nano SiC imbedded with fibers to improve properties, especially in high temperature applications .The least common composite matrix. Polymer Matrix Composites (PMCs) - thermosetting resins are widely used in PMCs .xamples: epoxy and polyester with fiber reinforcement, and phenolic with powders.1.7 METAL MATRIX COMPOSITES (MMCs)

Metal matrix Nano composites are composed of a metallic matrix (Al, Mg, Fe, Cu etc) and a dispersed ceramic (oxide, carbides) or metallic phase(Pb, Mo, W etc). Ceramic reinforcement may be Nano Silicon Carbide, boron, alumina, silicon nitride, boron carbide, boron nitride etc. whereas Metallic reinforcement may be tungsten, beryllium etc. MMNCs are used for Space Shuttle, commercial airlines, electronic substrates, bicycles, automobiles, golf clubs and a variety of other applications. From a material point of view, when compared to polymer matrix composites, the advantages of MMNCs lie in their retention of strength and stiffness at elevated temperature, good abrasion and creep resistance properties.Most MMNCs are still in the development stage or the early stages of production and are not so widely established as polymer matrix composites. The biggest disadvantages of MMNCs are their high costs of fabrication, which has placed limitations on their actual applications. There are also advantages in some of the phyNano SiCal attributes of MMNCs such as no significant moisture absorption properties, non-in flammability, low electrical and thermal conductivities and resistance to most radiations. MMNCs have existed for the past 30 years and a wide range of MMNCs have been studied.

1.7.1 Properties of MMNCs

Compared to monolithic metals, MMNChave: High strength High modulus High toughness and impact properties Low sensitivity to changes in temperature or thermal shock High surface durability and low sensitivity to surface flaws High electrical conductivity Excellent reproducibility of properties

1.7.2 Most widely used Metal Matrix Nano Composites

Numerous combinations of matrices and reinforcements have been tried since work on MMNC began in the lathe 1950s. However, MMNC technology is still in the early stages of development and other important systems undoubtedly will emerge. Numerous metals have been used as matrices. The most important have been aluminium, titanium, magnesium and copper alloys.The most important MMNC systems are Aluminium matrixi. Continuous fibres: Boron, Nano Silicon Carbide, alumina, graphite

ii. Discontinuous fibres: Alumina, alumina-silica

iii. Whiskers: Nano Silicon Carbide

iv. Particulates: Nano Silicon Carbide, boron carbide

Magnesium matrixi. Continuous fibres: graphite, alumina

ii. Whiskers: Nano Silicon Carbide

iii. Particulates: Nano Silicon Carbide, boron carbide

Titanium matrixi. Continuous fibres: Nano Silicon Carbide, coated boron

ii. Particulates: titanium carbide

Copper matrixi. Continuous fibres: graphite, Nano Silicon Carbide

ii. Wires: niobium-titanium, niobium-tin

iii. Particulates: Nano Silicon Carbide, boron carbide, titanium carbide.

1.8 FABRICATION METHODS

Many methods are available to fabricate the composites, depending on the final part geometry and geometry requirements. Aluminium MMCs are mostly produced by casting, powder metallurgy, in situ development of reinforcements, and foil-and-fibre pressing techniques. As the squeeze casting method is cheaper one and it is becoming the more commonly used method of fabrication of defect free products. In this method, the reinforcement particles and the matrix are heated to the required temperature. Then they are stirred and placed in the squeeze cast die, where they are pressurized during a controlled solidification process. Selectively reinforced MMCs made with process exhibit high tensile and fatigue strength based on a fine grain microstructure and limited micro porosity. Fabrication methods are an important part of the design process for all structural materials, including MMCs. Considerable work is under way in this critical area. Significant improvements in existing processes and development of new ones appear likely. Current methods can be divided into two major categories, primary and secondary. These methods can be divided into 4 broad senses: Powder processes Deposition processes Liquid processes Solid state processesProblems vary with the particular matrix-fiber combination being considered but at least these three must always be kept in mind: Reaction between fibers and matrix at elevated temperatures, either as the composite is being prepared or under service conditions Obtaining sufficient bonding between the matrix and the fibers Alignment of fibers within the matrix

Powder Metallurgy:The powder metallurgy technique usually employs whiskers or cut fibers of the reinforcing materials. These are nixed with the matrix powder and then pressed to consolidate the matrix. This may or may not be followed by sintering to improve matrix density. A major problem when using powder metallurgy is the elimination of porosity. There is also difficulty in obtaining alignment of the reinforcing material.Pneumatic Impaction:Pneumatic impaction can be considered as a variation of powder metallurgy since a powdered matrix is employed. The mixture of powder and reinforcing fiber is prepared and high unit pressure is applied by means of an impacter or a Dynapak machine.Plasma Spray Deposition of Matrix:This is a combination of a powder process and liquid process and also involves hot pressing. A layer of fibers is laid up on a rotating mandrel, the metal is deposited on the fibers by plasma spraying, a second layer of fibers is put on, and the operations are repeated until the desired thickness and the number of layers is attained.Vapor Deposition:Vapor deposition is a process where the reinforcement, particularly whiskers are coated by the matrix material from the deposition of its compounds. Extrusion process is finally employed for orienting the whiskers parallel to the extrusion axis.Electroforming:This process is especially used to prepare composites of boron in aluminum matrix. A continuous boron filament is on a mandrel is immersed in a solution. Aluminum is continuously plated from this bath as the filament is wound.Vacuum Infiltration of Fibers by Molten Metal:This is a method for preparations of small specimens of composites containing metallic or ceramic fibers in aluminum, magnesium, silver, copper and alloy matrices whose melting points are quite low. The composites were formed under vacuum by casting the matrix around the coated filaments.Fusion casting:There are two approaches of making a composite, which can be considered as a casting. In first method, a continuous reinforcing filament is fed through a pot of molten metal.The other way is the introduction of molten metal into, around and through mats or bundles of fibers or whiskers.Unidirectional Solidification of Eutectic Alloy:Another method of composite formation is growth from a melt at certain temperatures and for some time ranges.Co-extrusion:Co-extrusion is a method that has been employed for the incorporation of continuous wires or filaments to matrix. Since the matrix is worked by extrusion, it will contribute appreciable strength to the composite.Rolling:Hot or cold rolling can be employed to consolidate coated continuous fibers or to introduce continuous fibers or wires in matrix metal strips.Diffusion Bonding:In this method, alternate layers of matrix foil and properly spaced and oriented reinforcing fibers are laid down until the necessary amount of material for the desired final thickness is assembled. Then, by a combination of heat, pressure and time in a vacuum, the matrix is caused to flow around the fibers and bond to the next layer of matrix and at the same time grip the reinforcing fiber very tightly.1.9 WEAR

In Material science, wear is the erosion of material from a solid surface by the action of another surface. It is related to surface interactions and more specifically the removal of material from a surface as a result of mechanical action. The need for mechanical action, in the form of contact due to relative motion, is an important distinction between mechanical wear and other processes with similar outcomes.1.9.1 Wear Characteristics

The definition of wear does not include loss of dimension from plastic deformation although wear has occurred despite no material removal. This definition also fails to include impact wear, where there is no sliding motion, cavitation where the counter body is a fluid, and corrosion where the damage is due to chemical rather than mechanical action. Wear can also be defined as a process in which interaction of the surfaces or bounding faces of a solid with its working environment results in dimensional loss of the solid, with or without loss of material. Aspects of the working environment which affect wear include loads (such as unidirectional sliding, reciprocating, rolling, and impact loads), speed, temperature, type of counter body (solid, liquid and gas), and type of contact(single phase or multiphase, in which the phases involved can be liquid plus solid particles plus gas bubbles).

1.9.2 Classification of Wear

The study of the processes of wear is part of the discipline of tribology. The complex nature of wear has delayed its investigations and resulted in isolated studies towards specific wear mechanisms or processes. Some commonly referred to wear mechanisms (or processes) include:

Adhesive wear Abrasive wear Surface fatigue Fretting wear

1.9.3 Erosive Wear A number of different wear phenomena are also commonly encountered and represented in literature. Impact wear, cavitation wear, diffusive wear and corrosive wear are all such examples. These wear mechanisms; however, do not necessarily act independently in many applications. Wear mechanisms are not mutually exclusive. "Industrial Wear" is the term used to describe the incidence of multiple wear mechanisms occurring in unison. Wear mechanisms and/or sub-mechanisms frequently overlap and occur in a synergistic manner, producing a greater rate of wear than the sum of the individual wear mechanisms.

1.9.4 Adhesive WearAdhesive wear occurs when two smooth bodies are slide over each other, or pressed into one another and fragments are pulled off one surface and adhere to the other, due to the strong adhesive forces between atoms. It is the most common form of wear and is commonly encountered in conjunction with lubricant failures. It is commonly referred to as welding wear due to the exhibited surface characteristics. The tendency of contacting surfaces to adhere arises from the attractive forces that exist between the surface atoms of the two materials. The type and mechanism of attraction varies between different materials. Most solids will adhere on contact to some extent, however, oxidation films and contaminants naturally occurring, generally suppress adhesion. Surfaces also generally have low energy states due to reacted and absorbed species. The mechanism of adhesive wear occurs due to contact possibly producing surface plastic flow, scraping off soft surface films or breaking up and removing oxide layers. This brings clean regions into contact and introduces the possibility of strong adhesion. The removal of material, or wear, takes the form of small particles. These small particles are usually transferred to the other surface but may come off in loose form.

1.9.5 Abrasive WearAbrasive wear occurs when a hard rough surface slides across a softer surface. ASTM (American Society for Testing and Materials) define it as the loss of material due to hard particles or hard protuberances that are forced against and move along a solid surface. Abrasive wear is commonly classified according to the type of contact and the contact environment. The type of contact determines the mode of abrasive wear. The two modes of abrasive wear are known as two-body and three-body abrasive wear. Two-body wear occurs when the grits, or hard particles, are rigidly mounted or adhere to a surface, when they remove the material from the surface. The common analogy is that of material being removed with sand paper. Three-body wear occurs when the particles are not constrained, and are free to roll and slide down a surface. The contact environment determines whether the wear is classified as open or closed. An open contact environment occurs when the surfaces are sufficiently displaced to be independent of one another.

1.9.6 Surface FatigueSurface fatigue is a process by which the surface of a material is weakened by cyclic loading, which is one type of general material fatigue.1.9.7 Fretting WearFretting wear is the repeated cyclical rubbing between two surfaces, which is known as fretting, over a period of time which will remove material from one or both surfaces in contact. It occurs typically in bearings, although most bearings have their surfaces hardened to resist the problem. Another problem occurs when cracks in either surface are created, known as fretting fatigue. It is the more serious of the two phenomena because it can lead to catastrophic failure of the bearing. An associated problem occurs when the small particles removed by wear are oxidized in air. The oxides are usually harder than the underlying metal, so wear accelerates as the harder particles abrade the metal surfaces further. Fretting corrosion acts in the same way, especially when water is present. Unprotected bearings on large structures like bridges can suffer serious degradation in behaviour, especially when salt is used during winter to deice the highways carried by the bridges. The problem of fretting corrosion was involved in the silver bridge tragedy and the Mianus River bridge accident.1.10 HARDNESSThe Metals Handbook defines hardness as "Resistance of metal to plastic deformation, usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting. It is the property of a metal, which gives it the ability to resist being permanently, deformed (bent, broken, or have its shape changed), when a load is applied. The greater the hardness of the metal, the greater resistance it has to deformation.The followings are the most common hardness test methods used in today`s technology: Rockwell hardness test Brinell hardness Vickers Knoop hardness Micro hardness Test Moh's Hardness Test Scleroscope and other hardness test methods1.10.1 Rockwell Hardness TestThe Rockwell Hardness test is a hardness measurement based on the net increase in depth of impression as a load is applied. Hardness numbers have no units and are commonly given in the R, L, M, E and K scales. The higher the number in each of the scales means the harder the material.Hardness has been variously defined as resistance to local penetration, scratching, machining, wear or abrasion, and yielding. The multiplicity of definitions, and corresponding multiplicity of hardness measuring instruments, together with the lack of a fundamental definition, indicates that hardness may not be a fundamental property of a material, but rather a composite one including yield strength, work hardening, true tensile strength, modulus of elasticity, and others. In the Rockwell method of hardness testing, the depth of penetration of an indenter under certain arbitrary test conditions is determined.1.10.2 Brinell Hardness TestBrinell hardness is determined by forcing a hard steel or carbide sphere of a specified diameter under a specified load into the surface of a material and measuring the diameter of the indentation left after the test. The Brinell hardness number, or simply the Brinell number, is obtained by dividing the load used, in kilograms, by the actual surface area of the indentation, in square millimeters. The result is a pressure measurement, but the units are rarely stated.

1.10.3 Vickers Hardness TestThe Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation.

F= Load in kgfd = Arithmetic mean of the two diagonals, d1 and d2 in mm HV = Vickers hardness

When the mean diagonal of the indentation has been determined the Vickers hardness may be calculated from the formula, but is more convenient to use conversion tables. The Vickers hardness should be reported like 800 HV/10, which means a Vickers hardness of 800, was obtained using a 10 kgf force. Several different loading settings give practically identical hardness numbers on uniform material, which is much better than the arbitrary changing of scale with the other hardness testing methods.

The advantages of the Vickers hardness test are that extremely accurate readings can be taken, and just one type of indenter is used for all types of metals and surface treatments. Although thoroughly adaptable and very precise for testing the softest and hardest of materials, under varying loads, the Vickers machine is a floor standing unit that is more expensive than the Brinell or Rockwell machines.

There is now a trend towards reporting Vickers hardness in SI units (MPa or GPa) particularly in academic papers. Unfortunately, this can cause confusion. Vickers hardness (e.g. HV/30) value should normally be expressed as a number only (without the unitskgf/mm2). Rigorous application of SI is a problem. Most Vickers hardness testing machines use forces of 1, 2, 5, 10, 30, 50 and 100 kgf and tables for calculating HV. SI would involve reporting force in newtons (compare 700 HV/30 to HV/294 N = 6.87 GPa) which is practically meaningless and messy to engineers and technicians. To convert Vickers hardness number the force applied needs converting from kgf to newtons and the area needs converting from mm2 to m2 to give results in pascals using the formula above. To convert HV to MPa multiply by 9.807 To convert HV to GPa multiply by 0.009807

CHAPTER 2

LITERATURE REVIEW

2.1 REVIEW OF LITERATURE

Composite materials open up unlimited possibilities for modern material science and development. The characteristics of MMCs can be designed into the material, custom-made based on the application. The possibility of combining various material systems (Metal+ ceramic+ non metal) gives the opportunity for unlimited variation. However, the advantages of the composite materials are only realized when there is a reasonable cost vs performance relationship in the component production. The properties of these new materials are basically determined by the properties of their single component. For better understanding detailed survey on the relevant literature has been carried out and is presented in this chapter.

Alaneme et.al.,(2013) discussed the viability of developing low cost high performance Al matrix hybrid composites with the use of bamboo leaf ash (an agro waste ash) and Silicon Carbide as complementing reinforcements was investigated. Silicon Carbide(SiC) particulates added with 0, 2, 3, and 4 wt% bamboo leaf ash (BLA) were utilized to prepare 10 wt% of the reinforcing phase with Al Mg Si alloy as matrix using two step stir casting method. [1]

Subrata Kumar Ghosh & Partha Saha (2011) discovered that crack density and wear performance of SiC particulate (SiCp) reinforced Al-based metal matrix composite (Al-MMC) fabricated by direct metal laser sintering (DMLS) process have been studied. Mainly, size and volume fraction of SiCp have been varied to analyze the crack and wear behavior of the composite. The study has suggested that crack density increases significantly after 15 volume percentage (vol.%) of SiCp. The paper has also suggested that when size (mesh) of reinforcement increases, wear resistance of the composite drops. Three hundred mesh of SiCp offers better wear resistance; above 300 mesh the specific wear rate increases significantly. Similarly, there has been no improvement of wear resistance after 20 vol.% of reinforcement. [2]

In the paper presented by Deepak Singlhla the effects of load and sliding speed on the friction coefficient and wear properties of pin of Al 7075-Fly Ash composite material on Pin on Disc apparatus were investigated. Composites are most successful materials used for recent works in the industry. Metal composites possess significantly improved properties including hardness and wear resistance compared to alloys or any other metal. Hence composites with fly ash with Al 7075 as reinforcement are optimizes the different physiCal and mechanical properties which widely used in the automotive and space craft applications. [3]

Deuis R.L et al.,(1996) investigated Aluminium-silicon alloys and aluminium based metal matrix composites have found application in the manufacture of various automotive engine components such as cylinder blocks, pistons and piston insert rings where adhesive wear (or dry sliding wear) is a predominant process. For adhesive wear, the influence of applied load, sliding speed, wearing surface hardness, reinforcement fracture toughness and morphology are critical parameters in relation to the wear regime encountered by the material. In this review contemporary wear theories, issues related to counter face wear, and wear mechanisms are discussed. [4]

Rajesh Purohit used a horizontal ball mill for the milling of aluminum and Nano SiC particles. The change in powder particle morphology during mechanical alloying of Aluminum and SiC powders using horizontal ball mill was studied. Al SiCp composites with 5 to 30 weight% of SiCp were fabricated using powder metallurgy process. The various properties viz. hardness, density, porosity, compressive strength, indirect tensile strength and surface roughness were measured. The density, porosity, hardness, compressive strength and indirect tensile strength of Al-SiCp composites were found to increase with increase in the wt.% of SiCp from 5 to 30 weight percent. Mechanical alloying of powders resulted in improvement in hardness and compressive strength of Al-Nano SiCp composites with 5 to 30 weight% of Nano SiCp. The microstructure of polished and etched surfaces of powder metal Al-Nano SiCp composite samples was studied using scanning electron microscope. [5]

In the present study made by Gaurav Chigal modest attempt has been made to develop aluminium based Silicon Carbide particulate MMCs with an objective to develop a conventional low cost method of producing MMCs and to obtain homogenous dispersion of ceramic material. To achieve these objectives two step-mixing method of stir casting technique has been adopted and subsequent property analysis has been made. Aluminium6061 (97.06% C.P) and SiC (320-grit) has been chosen as matrix and reinforcement material respectively. Experiments have been conducted by varying weight fraction of Nano SiC (2.5%, 5%, and 10%) while keeping all other parameters constant. The results indicated that the developed method is quite successful to obtain uniform dispersion of reinforcement in the matrix. An increasing trend of Tensile Test with increase in weight percentage of SiC has been observed. The results were further justified by comparing with other investigators. [6]

The mechanical and wear properties of hybrid aluminium metal matrix composites were investigated by T.Raj Mohan. Mica and SiC ceramic particles were incorporated into Al 356 alloy by stir-casting route. Microstructures of the samples were studied using scanning electron microscope (SEM). The chemical composition was investigated through energy dispersive X-ray (EDX) detector. The results indicate that the better strength and hardness are achieved with Al/10Nano SiC3mica composites. The increase in mass fraction of mica improves the wear loss of the composites. [7]

Prashant Kumar investigated about producing aluminium based metal matrix composite and then studying its microstructure and mechanical properties such as tensile strength, impact strength and mar behavior of produced test specimen. In the present study a modest attempt has been made to develop aluminium based WCs with reinforcing material, with an objective to develop a conventional low cast method of producing WCs and to obtain homogeneous dispersion of reinforced material. To achieve this objective stir casting technique has been adopted Aluminium Alloy (LM6) and ,S C, Fly Ash has been chosen as matrix and reinforcing material respectively. Experiment has been conducted by varying 'might fraction of Fly Ash (S% and 15%) while keeping SiC constant(5%). The result shown that the increase in addition of Fly Ash increases the Tensile Strength Impact Strength Wear Resistance of the specimen and decreases the percentage of Elongation. [8]

Dunia Abdul Saheb aimed to achieve a uniform distribution of reinforcement within the matrix is one such challenge, which affects directly on the properties and quality of composite. In his study an attempt has been made to develop aluminium based Silicon Carbide particulate MMCs, graphite particulate MMCs with an objective to develop a conventional low cost method of producing MMCs and to obtain homogenous dispersion of ceramic material. Experiments have been conducted by varying weight fraction of SiC, graphite and alumina (5%, 10%, 15%, 20%, 25%, and 30%), while graphite weight fraction 2%, 4%, 6%, 8% and 10% keep all other parameters constant. The results indicated that the developed method is quite successful to obtain uniform dispersion of reinforcement in the matrix. An increasing of hardness and with increase in weight percentage of ceramic materials has been observed. The best results (maximum hardness) have been obtained at 25 % weight fraction of SiC and at 4% weight fraction of graphite. [9]

In the present research by Mohammad Asaduzzaman, friction coefficients of stainless steel 304 (SS 304) sliding against different pin materials were investigated and compared. In order to do so, a pin on disc apparatus is designed and fabricated. Experiments are carried out when different types of pin such as aluminum, gun metal, copper and brass slide on SS 304 disc. Experiments are conducted at normal load 10, 15 and 20 N, sliding velocity 1, 1.5 and 2 m/s and relative humidity 70%. Variations of friction coefficient with the duration of rubbing at different normal load and sliding velocity are investigated. Results show that friction coefficient varies with duration of rubbing, normal load and sliding velocity. In general, friction coefficient increases for a certain duration of rubbing and after that it remains constant for the rest of the experimental time. The obtained results reveal that friction coefficient decreases with the increase in normal load for all the tested pairs. On the other hand, it is also found that friction coefficient increases with the increase in sliding velocity. Moreover, wear rate increases with the increase in normal load and sliding velocity for all sliding pairs. The magnitudes of friction coefficient are different for different material pairs depending on normal load and sliding velocity. [10]

Balasivanandha Prabu et al., investigated that better stir process and stir time. The high silicon content aluminium alloy Silicon Carbide MMC material, with 10% SiC by using a variance stirring speeds and stirring times. The microstructure of the produced composite was examined by optical microscope and scanning electron microscope. The results with respected to that stirring speed and stirring time influenced the microstructure and the hardness of composite. Also they investigate that at lower stirring speed with lower stirring time, the particle group was more. Increase in stirring time and speed resulted in better distribution of particles. The mechanical test results also revealed that stirring speed and stirring time have their effect on the hardness of the composite. The uniform hardness valued was achieved at 600 rpm with 10min stirring. But above this stir speed the properties degraded again. [11]

Mahendra Boopathi.M et al[2]., experimented to Development of hybrid metal matrix composites has become an important area of research interest in materials science. In view of this, the present study was aimed at evaluating the physical properties of aluminium 2024 in the presence of fly ash, Silicon Carbide and its combinations. Consequently aluminium MMC combination the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. Stir casting method was used for the fabrication of aluminium MMC. Structural characterization was carried out on MMC by x-ray diffraction studies and optical microscopy was used for the micro structural studies. The mechanical of MMC like density, elongation, hardness, yield strength and tensile test were ascertained by performing carefully designed laboratory experiments that replicate as nearly as possible the service conditions. In the presence of fly ash and Silicon Carbide [SiC (5%) + fly ash (10%) and fly ash (10%) + SiC (10%)] with aluminium, the result show that the decreasing the density with increasing harness and tensile strength was also observed but elongation of the hybrid MMC in comparison with unreinforced aluminium was decreased. The hybrid metal matrix composites significantly differed in all of the properties measured. Aluminium in the presence of SiC (10%)-fly ash (10%) was the hardest instead of aluminium SiC and aluminium fly ash composites. [12]

Martin I. Pech-Canul et al[3].,with all the valuable research work conducted thus far in the field, there can be no denying that aluminum plays a pivotal role in the development of composite materials reinforced with SiC. It turns out that alloy composition influences the processing route to be employed as well as the mechanical, heat-treatment and corrosion behavior of the composites. The use of aluminum in liquid state has serious implications because attack of SiC and the subsequent phenomena do compromise the integrity of the composite. In this regard, since the aluminum-matrix/reinforcement interface plays a critical role in transferring the load from the matrix to the reinforcing phase, the soundness of the interface is always a crucial aspect to take care of. What's more, wettability studies aimed at optimizing processing conditions are always wise. From heat treatment investigations, there is a consensus in that SiC in aluminum leads to an accelerated age hardening, compared to the unreinforced alloy. Being pitting one of the major concerns in the corrosion behavior of Al/ SiC composites, the confluence of results suggest that in the composites, pitting is greater in number, smaller in size and shallower in penetration depth, relative to the unreinforced aluminum alloys. Since pits initiate at secondary particles within the metal matrix, and as a greater number of intermetallic phases form in the composites, these have more pit initiation sites. It is suggested from this discussion that corrosion tests should precede mechanical evaluation involving hardness, creep and fatigue and fracture studies. A thoughtful consideration of the abovementioned factors and response variables involved increases the likelihood for Al/SiC composites to achieve their full potential in a safe and cost-effective way. [13]

Ali MAZAHERY, et. Al[4], studied that the effect of SiC particles reinforcement with average size of 1, 5, 20 and 50 m and volume fraction of 5%, 10% and 15% on the microstructure and tribological properties of Al-based composite was investigated. Composites were produced by applying compocasting process. Tribological properties of the unreinforced alloy and composites were studied using pin-on-disc wear tester, under dry sliding conditions at different specific loads. The influence of secondary mechanical processing with different rolling reductions on the dry sliding wear characteristics of Al matrix composites was also assessed. The proper selection of process parameter such as pouring temperature, stirring speed, stirring time, pre-heated temperature of reinforcement can all influence the quality of the fabricated composites. The porosity level of composite should be minimized and the chemical reaction between the reinforcement and matrix should be avoided. [14]

2.2 IDENTIFIED GAPS IN LITERATURE

From the literature survey carried out it can be summarized up as following

Efforts should be made on the development of Aluminium metal matrix with Nano SiC as the reinforcement material.

Work should be done to find the most suitable method for fabricating metal matrix composites.

There is a need to improve wear resistance and hardness in aluminium alloy (Al6061) by varying the weight fraction of reinforcement.

2.3 OBJECTIVES

Accordingly the objectives of the present study are

To develop a Metal matrix composite with high quality Nano Silicon Carbide (50 A.P.S) and study the wear characteristics and hardness.

To develop a Metal matrix composite with various volume fractions (0.5%, 1%, 1.5%) of Nano Silicon Carbide as reinforcements.

To analyze and compare the MMC prepared with various volume fractions for the wear characteristics and hardness.

CHAPTER 3METHODOLOGY3.1 STEPS INVOLVED

3.2 MATERIAL SELECTION

Aluminium (Al6061) is selected as the matrix material. Aluminium alloy 6061 is one of the most extensively used of the 6000 series Aluminium alloys.

3.2.1 Chemical Composition of Al6061:Elements SymbolUnitSpecified ValuesObserved Values

SiliconSi%0.40 - 0.800.643

IronFe%0.70 Max0.129

CopperCu%0.15 - 0.400.254

ManganeseMn%0.15 Max0.044

MagnesiumMg%0.8 - 1.200.944

ChromiumCr%0.04 0.350.093

ZincZn%0.25 Max0.017

TitaniumTi%0.15 ax0.017

AluminiumAl%RemainderRemainder(97.80)

Table 3.1 Chemical Composition of Al6061

3.2.2 Characteristics of Al6061

The heat treated alloy has fairly good machining properties.

The alloy has fairly good resistance to corrosion under atmospheric conditions. A protective film, usually greyish in colour, may be obtained by either the sulphuric or chromic acid process.

Al6061 has good weldability.

Full heat treatment gives high strength and hardness3.2.3 Applications of Al6061

Alloy 6061 is typically used for heavy duty structures in: Rail coaches Truck frames Ship building Bridges and Military bridges Aerospace applications including helicopter rotor skins Tube Pylons and Towers Transport Boiler making Motorboats Rivets3.2.4 Physical Properties of Al6061 Density2.70 g/cm Melting Point650 C Thermal Expansion23.4 x10^-6 /K Modulus of Elasticity70 GPa Thermal Conductivity 166 W/m.K Electrical Resistivity0.040 x10^-6 .m

3.2.5 Mechanical properties of Al6061

The mechanical properties of the matrix material are given in the Table 3.2. This alloy conforms to BS 1490:1998 Al6061. Castings are standardized in the solution treated and naturally aged condition and in the fully heat treated condition.

TemperUltimate Tensile Strength (MPa)0.2% Proof Stress (MPa)Brinell Hardness (500kg load, 10mm ball)Elongation 50mm dia (%)

0110-15265-11030-3314-16

T118095-9616

T4179 min110 min

T6260-310240-27695-979-13

Table 3.2 Mechanical properties of Al6061

3.2.5 Casting Characteristics of Al6061

Fluidity - an intermediate between Aluminium-nano Silicon and Aluminium- Copper alloys.

Pressure tightness - suitable for leak tight castings

Typical pouring temperature - 993K the actual temperaturesemployed may range considerably above or below this value and will depend upon the particular for each casting.

3.2.6 Nano Silicon Carbide

The Nano Silicon Carbide particulate (Nano SiC) is used as a reinforcement material which size range is 50nm Nano Silicon Carbide is light weight and greenish black in colour.

The chemical formula for Nano Silicon Carbide is Nano SiC It is having high degree of brightness, low plasticity, ease of dispersion.

It is having low bulk density and very low moisture content. It improves electrical as well as mechanical properties.

Nano Silicon Carbide is the only chemical compound of carbon and silicon. It was originally produced by a high temperature electro-chemical reaction of sand and carbon. Nano Silicon Carbide is an excellent abrasive and has been produced and made into grinding wheels and other abrasive products for over one hundred years. Today the material has been developed into a high quality technical grade ceramic with very good mechanical properties. It is used in abrasives, refractories, ceramics, and numerous high-performance applications. The material can also be made an electrical conductor and has applications in resistance heating, flame igniters and electronic components. Structural and wear applications are constantly developing.3.2.7 Properties of Nano Silicon Carbide Low density High strength Low thermal expansion High thermal conductivity High hardness High elastic modulus Excellent thermal shock resistance3.2.8 Uses of Nano Silicon Carbide Fixed and moving turbine components Suction box covers Seals, bearings Ball valve parts Hot gas flow liners Heat exchangers Semiconductor process equipment3.2.9 General Nano Silicon Carbide Information Nano Silicon Carbide is composed of tetrahedra of carbon and silicon atoms with strong bonds in the crystal lattice. This produces a very hard and strong material. Nano Silicon Carbide is not attacked by any acids or alkalis or molten salts up to 800C. In air, Nano SiC forms a protective silicon oxide coating at 1200C and is able to be used up to 1600C. The high thermal conductivity coupled with low thermal expansion and high strength give this material exceptional thermal shock resistant qualities. Nano Silicon Carbide ceramics with little or no grain boundary impurities maintain their strength to very high temperatures, approaching 1600C with no strength loss.

Fig 3.1 Silicon Carbide nanopowder Chemical purity, resistance to chemical attack at temperature, and strength retention at high temperatures has made this material very popular as wafer tray supports and paddles in semiconductor furnaces. The electrical conduction of the material has lead to its use in resistance heating elements for electric furnaces, and as a key component in thermistors (temperature variable resistors) and in varistors (voltage variable resistors).

MechanicalSI/Metric (Imperial)SI/Metric(Imperial)

Densitygm/cc (lb/ft3)3.1(193.5)

Porosity% (%)0(0)

Colorblack

Flexural StrengthMPa (lb/in2x103)550(80)

Elastic ModulusGPa (lb/in2x106)410(59.5)

Shear ModulusGPa (lb/in2x106)

Bulk ModulusGPa (lb/in2x106)

Poissons Ratio0.14(0.14)

Compressive StrengthMPa (lb/in2x103)3900(566)

Table 3.3 Nano Silicon Carbide Engineering Properties

ThermalSI/Metric (Imperial)SI/Metric(Imperial)

Thermal ConductivityW/mK (BTUin/ft2hrF)120(830)

Coefficient of Thermal Expansion106/C (106/F)4.0(2.2)

Specific HeatJ/KgK (Btu/lbF)750(0.18)

Dielectric Strengthac-kv/mm (volts/mil)semiconductor

Volume Resistivityohmcm102106dopant dependent

Table 3.4 Nano Silicon Carbide Thermal Properties

3.3 SELECTION OF FABRICATION TECHNIQUE

A variety of processes have been developed and being used for the manufacture of MMNCs. These may be divided into primary material production and secondary consolidation for forming operations. A further important distinction can be drawn for the primary process depending on whether the matrix becomes liquid at any stage. Each technique has its own limitations in terms of component size and shape and impose certain micro structural features on the product.

3.3.1 Fabrication of Composite

Various methods are used to form composite, depending on the final part geometry and property requirements. For aluminium MMCs, particulate reinforced parts can be formed by the both wrought and casting process, and the entire part is reinforced. For fiber or whisker reinforced parts, pressure or vacuum/pressure casting processes are used. Lower cost squeeze casting is becoming a more commonly used method of fabrication. In this method, reinforcement preforms are placed in the steel squeeze cast die where they are desired in the final part, the die closes, and molten aluminium is pumped in and pressurized during a controlled solidification process. Selectivity reinforced MMCs made with this process exhibit high tensile and fatigue strengths based on a fine gain microstructure and limited micro porosity. In this study the fabrication was carried out by stir casting. Then the wear test was carried out on the specimens using pin on disc to predict the abrasive wear behaviour of the composites and the hardness test was carried out on the specimens using Vickers hardness instrument to investigate the property of hardness of the composites.

3.3.2 Stir casting In a stir casting process, the reinforcing phases are distributed into molten matrix by mechanical stirrer. Mechanical stirring in the furnace is a key element of this process. The resultant molten alloy, with ceramic particles, can then be used for die casting, permanent mold casting, or sand casting. Stir casting is suitable for manufacturing composites with up to 30% volume fractions of reinforcement. An interesting recent development in stir casting is a two-step mixing process. In this process, the matrix material is heated to above its liquids temperature so that the metal is totally melted. The melt is then cooled down to a temperature between the liquids and solidus points and kept in a semi-solid state. At this stage, the preheated particles are added and mixed. The slurry is again heated to a fully liquid state and mixed thoroughly. This two-step mixing process has been used in the fabrication of aluminum

CHAPTER 4

EXPERIMENTAL WORK

4.1 FABRICATION OF NANOCOMPOSITE

The Stir casting method was used to prepare nano composites. The Al alloy pieces were heated to 1100C in a graphite crucible. The reinforcement particulates Nano SiC and magnesium (20%wt) are preheated for 30 minutes. Magnesium is added to promote wettability. Aluminium degassing tablets are added in the powdered form to remove the bubbles formed during the process. The heated slurry was stirred at 310 rpm for 8-10 minutes using a three blade mild steel impeller to ensure uniform incorporation of the Nano SiC particles into the Aluminium matrix.

The three blade mild steel impeller was coated with alumina powder to avoid iron contamination of the molten Al metal. The impeller was placed just 20 mm above the bottom of the graphite crucible, and the blades of the impeller (tilted at an angle of 45), when rotated, covered a relatively large area of the crucible base. This design prevented the heavier Nano Nano SiC from settling when the melted slurry was stirred for 5 minutes. Furthermore, stirring at an optimized speed of 310 rpm created a vortex in the melt, and this effectively enhanced the distribution of the particles.

.

Fig 4.1 Principle of Stir casting technique

This stirring process was used to ensure the homogeneity of the melted slurry. The melt, with incorporated Nano SiC and particles, are poured in to a mould of length 200mm and diameter 20mm as a rod and also 95mm diameter & 10mm thickness.

Fig 4.2 Addition of Nano SiC Fig 4.3 Stirring of molten slurry

4.2 TESTING

Following tests were conducted on various mechanical and physical properties of the composite specimens and their corresponding results are compared.

4.2.1 Hardness Test

Hardness may be defined as the resistance to plastic deformation by indentation. Vickers hardness is a measure of the hardness of a material, calculated from the size of an impression produced under load by a pyramid-shaped diamond indenter. The Vickers test is reliable for measuring the hardness of metals, and also used on ceramic materials. The Vickers testing method is similar to the Brinell test. The other advantage of the Vickers system other than the increased degree of accuracy is that it does not have a number of different scales and indenters, as does the Rockwell and Brinell scales.Vicker Hardness is measured by forcing an indenter into the surface of the sample. It uses a 136 square pyramid indenter, which produces a square indentation in the specimen, rather than a spherical or conical indenter, which Rockwell and Brinell hardness techniques use. The square indenter is advantageous over the round indentations as the square indentations are easier to measure than the round impressions from spherical and conical indenters. The Vickers hardness tester is equipped with an adjustable height stage, which is wound up to close to the indenter prior to the test. Indenter load of 0.5 kg is applied. The indentation is then measured with a microscope across the diagonals of the square indentation.Usually the prepared samples are mounted in a Bakelite medium to facilitate the preparation and testing. The indentations should be as large as possible to maximize the measurement resolution.

Fig 4.4 Sample which is to be tested for Vickers hardness

4.2.2 Wear Testing

A number of wear test have been developed by committees an attempt to standardize wear testing for specific applications. In the results of standard wear tests, the material during wear is expressed in terms of volume.

4.2.3 The Pin on Disc Apparatus

The pin on disc tester is used for a quick and easy method of kinetic friction and sliding wear measurement .The pin on disc tester measures the friction and sliding wear properties of dry or lubricated surfaces of a variety of bulk materials and coatings. The Pin on Disc wear testing Apparatus consists of a rotating disc of the material to be tested against a stationary sphere, usually made of Cast Iron, referred to as the pin and is shown in Figure 4.5. Although the pin surface can also be wear and friction tested. The principle of pin on disc tester is shown in figure 4.6.The normal load, rotational speed, and the wear track diameter are all the set by the user prior to the pin on disc test.Figure 4.5 Principle of the Apparatus

Fig 4.6 Pin on disc apparatusFig 4.7 Top view

Dry sliding wear tests were conducted using a pin-on-disc tester. Pin specimens of diameter 8mm and length 30 mm were machined from the extruded rods. Contact surfaces were prepared by grinding against 600-grit silicon carbide paper and cleaning with alcohol. A pin holder loaded the stationary pins vertically onto a rotating En-31 steel disc. The Figure 4.8 and Figure 4.9 shows the photo macrograph of En-31 Steel disc and photo macrograph of Al-Nano SiC composite pin respectively.

Fig 4.8 En-31 Steel discFig 4.9Al-Nano SiC composite pin

A normal load of 9.81 Kg was applied using dead weights at 1273 rpm. For each sliding condition, 8.02 minutes of run were carried out.. At the end of 8.02 minutes, the pins were carefully cleaned and weighed using a sensitive electronic balance with an accuracy of 0.1 mg to determine the weight loss. Wear studies were conducted on the extruded Al-Nano SiC nano composite samples in order to determine the co-efficient of friction..

CHAPTER 5RESULTS AND DISCUSSIONThe experimental results of Hardness test and Wear test of Al-Nano SiC composite are discussed in the following sections.

5.1 HARDNESS TEST

Vickers hardness test was done for measuring the hardness of Aluminium with Nano Silicon Carbide reinforced metal matrix composites. The test is executed with a lever or button, with all the rest of the test parameters being controlled automatically. Indenter load is kept at 0.5 kg. The indentation is then measured with a microscope across the diagonals of the square indentation.

The hardness values are taken in many places and in average the hardness of the Al-Nano SiC nano composite is calculated. The results of Al-Nano SiC nano composite hardness values are given in the Table 5.1.The hardness is calculated by dividing the load by the surface area of the indentation, such that Vickers hardness is determined using the following formula:

Where Hv = Vickers hardness (in MPa), F = load and A = surface area of the impression.

The comparison of mean hardness of the various percentage of Nano Silicon Carbide content with different samples in Figure 5.1Al-Nano SiC (0.5%)Al-Nano SiC(1%)Al-Nano SiC(1.5%)

Hardness(HV)(HV)(HV)

Trial 155.160.376.5

Trial 256.457.256.7

Trial 357.259.666.6

Trail 460.363.166.6

Average57.2560.0566.6

Table 5.1 Mean hardness of the various percentage of Nano Silicon Carbide content

Fig 5.1 Graph showing hardness of the various percentage of Nano Silicon Carbide content

Fig 5.2Graph showing Mean hardness of the various percentage of Nano Silicon Carbide contentFrom the above graphs, we can conclude that the hardness increases on the addition of Nano SiC.

5.2 WEAR TESTING

Immediately prior to testing, and prior to measuring or weighing, clean and dry the specimens. Take care to remove all dirt and foreign matter from the specimens. Measure appropriate specimen dimensions to the nearest 2.5 m or weigh the specimens to the nearest 0.0001 g. Insert the disk securely in the holding device so that the disk is fixed perpendicular to the axis of the resolution. Insert the pin specimen (8mm diameter 30mm length) securely in its holder and, if necessary, adjust so that the specimen is perpendicular to the disk surface when in contact, in order to maintain the necessary contact conditions. Add the proper mass to the system lever or bale to develop the selected force pressing the pin against the disk. Start the motor and adjust the speed to the desired value while holding the pin specimen out of contact with the disk. Stop the motor. Begin the test with the specimens in contact under load. The test is stopped when the desired number of revolutions is achieved. Tests should not be interrupted or restarted. Remove the specimens and clean off any loose wear debris. Note the existence of features on or near the wear scar such as: protrusions, displaced metal, discoloration, microcracking, or spotting. Remeasure the specimen dimensions to the nearest 2.5 nm or reweigh the specimens to the nearest 0.0001 g, as appropriate. Repeat the test with additional specimens to obtain sufficient data for statistically significant results.

The below table explains briefly about the wear loss for the applied load for Al-Nano SiC CompositesNano SiCBefore (g)After (g)Difference(g)

0.5%4.2464.2420.004

1%4.3104.3070.003

1.5%4.1854.1820.003

Table 5.2Table explains briefly about the wear loss for the applied load for

Al-Nano SiC Composites

The above table shows that addition of Nano SiC particulate in metal has decreased the wear. The below graphs shows coefficient of friction and wear for various samples.

Fig 5.3The graph shows wear rate for various samples of nano SiC

Fig 5.4The graph shows coefficient of friction for various samples ofnano SiC

The results obviously say that variation of co-efficient of friction and wear can be reduced by adding of Nano SiC particles with Al6061

CHAPTER 6CONCLUSION AND SCOPE OF FUTURE WORK6.1 CONCLUSIONExtensive literature survey has been carried out in the areas of matrix and reinforcement material combinations, composite manufacturing techniques and various mechanical testing methodologies.

From the literature survey, it is observed that increase in the volume fraction of reinforcement material increases the structural strength of the composite material but at the same time there is a drastic increase in wear resistance.

In this study Nano Silicon Carbide is selected as reinforcement material for making aluminium alloy composites by considering good mechanical and physical properties as other reinforcements currently used. Specimens were prepared for abrasion wear test and hardness test with required volume fraction reinforcement particulates by hybrid method of stir casting method.

Results show that Nano Silicon Carbide particles can be used as reinforcement material to improve the properties of the Al6061.

Aluminium reinforced with Nano SiC exhibits better dry abrasive wear resistance. The proper input parameters to achieve a specific output parameter (Coefficient of friction) and a higher efficiency can be determined by experimental characteristic diagrams. The wear rate decreases with increase of Nano SiC.

i. In the present investigation, addition of 1% Nano SiC particles reinforced composite exhibited better wear resistance than the other combinations. ii. This can also be implemented in several applications like piston in an engine cylinder and other aircrafts where the wear rates are higher. The hardness value also increases with increasing weight percentage of nano reinforcement. It shows that fabricated composite has higher strength.

6.2 SCOPE OF FUTURE WORK

The following recommendations could be fruitful for future works.

In Aerospace industry, they are focusing on the increased elevated temperature capability and improved fracture toughness, so the new developed composite may be incorporated. To the existing material, Nano SiC percentage can be increased so that the wear loss can be further decreased. By further heat treating, the composite material by advanced techniques the hardness of the material can be improved. If the same composite is done by powder metallurgy method, there might be a chance of increase in wear resistance. Vapour deposition technique can be implemented instead of stir casting so that resistance to corrosion can be increased.

REFERENCES1. Bharat Admile, S. G. Kulkarni, S. A. Sonawane, REVIEW ON MECHANICAL & WEAR BEHAVIOR OF ALUMINUM-FLYASH METAL MATRIX COMPOSITE, International Journal of Emerging Technology and Advanced Engineering, Volume 4, Issue 5 May 2014.

1. Deuis. Subramanian & Yellupb (1996), DRY SLIDING WEAR OF ALUMINIUM COMPOSITES-A REVIEW International Journal of Emerging Technology and Advanced Engineering Vol.57, pp. 415-435.

1. Dr.K.P. Dhanabalakrishnan, Dr.R.Subramanian, J.Abuthakir, S.Venkatesh, EVALUATION OF TENSILE PROPERTIES OF PARTICULATE REINFORCED Al-METAL MATRIX COMPOSITES IRACST Engineering Science and Technology: An International Journal (ESTIJ), ISSN: 2250-34981. Vol.5, No.1, February 2015.

1. Dunia Abdul Saheb, ALUMINUM SILICON CARBIDE AND ALUMINUM GRAPHITEPARTICULATE COMPOSITES,ARPN Journal of Engineering and Applied Sciences, Vol.6, No.10, OCTOBER 2011.

1. GauravChigal, GauravSaini, MECHANICAL TESTING OF AL6061/SILICON CARBIDE METAL MATRIX COMPOSITE, International Journal of Research in Engineering and Applied Sciences (IJREAS), Volume 2, Issue 2 (February 2012) ISSN: 2249-3905.

1. Manjunatha (2013), FABRICATION, MICROSTRUCTURE, HARDNESS AND WEAR PROPERTIES OF EXTRUDED MWCNT- REINFORCED WITH 6061AL METAL MATRIX COMPOSITES ARPN Journal of Engineering and Applied Sciences, Vol.4, pp.787-792.

1. Muruganandhan.P, Dr.Eswaramoorthi.M, ALUMINUM COMPOSITE WITH FLY ASH, IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE), Volume 11, Issue 6 Ver. III (Nov- Dec. 2014), pp.38-41.

1. Prez-Bustamante (2011), CHARACTERIZATION OF AL2024-CNTS COMPOSITES PRODUCED BY MECHANICAL ALLOYING, Journal of Materials Science, vol.212, pp.390-396.

1. Rajesh Purohit, R. S. Rana and C. S. Verma, FABRICATION OF AL-SICP COMPOSITES THROUGH POWDER METALLURGY PROCESS AND TESTING OF PROPERTIES, International Journal of Engineering Research and Applications (IJERA), Vol. 2, Issue 3, May-Jun 2012, pp. 420-437.

1. Rajmohan T, Palanikumar K, ARTIFICIAL NEURAL NETWORK MODEL TO PREDICT THRUST FORCE INDRILLING OF HYBRID METAL MATRIX COMPOSITES, National Journal on Advances in Building Sciences and Mechanics, Vol. 1, No.2, October 2010.

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