a literature survey study on metal and ceramic matrix composites_metal matrix composites

7/27/2019 A Literature Survey Study on Metal and Ceramic Matrix Composites_Metal Matrix Composites

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10/8/13 A literature survey study on Metal and Ceramic Matrix Composites/Metal Matrix Composites

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1. METAL MATRIX COMPOSITES

1.1. GENERAL PROPERTIES

The metal matrix composites have various advantages over other types of composites. Such as;

High strengthHigh modulusHigh toughness and impact propertiesLow sensit ivity to changes in temperature or thermal shockHigh surface durability and low sensitivity to surface flawsHigh electrical conductivityExcellent reproducibility of propertiesExcellent technological background with respect to

DesignManufactureShaping and forming

Joining and finishingService durability information

The high strength values of metal alloys, compared to structural ceramics or organicmaterials, which can be utilized in composite materials, make them attractive. Thishigh strength is mostly important with respect to composite properties at a directiondifferent from the reinforcement direction. Properties such as transverse strength,torsional strength and interlaminar shear strength are examples of matrix strengthcontrolled properties.

The high moduli of metal alloys compared to those of organic materials areparticularly significant in high modulus composites. Figure below shows a comparisonof several fiber-reinforced composite materials on the base of specific modulus (ininches).

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Fig. 1.1.

The high toughness and impact properties of metal alloys are very important, sincethe reinforcement is generally a linear elastic material and does not have good impactproperties. Ductile metal matrix alloys such as aluminum, titanium or nickel-chromium

alloys undergo energy-absorbing plastic deformation under impact, which is adesirable property for dynamic applications. The ductile metal matrix gives alsoimproved fracture toughness.

The comparably low thermal sensitivity of metal matrices enhances their uses in high-modulus structural composites. Other organic matrix materials are quite sensit ive totemperature changes. They are more resistant to thermal shocks the than ceramicmatrices are. At elevated temperatures, not only do they tend to soften but also theirresistance to oxidation, corrosion and erosion drops off s ignificantly.

The metal matrices are generally less sensitive to surface flaws than ceramics ororganic resins so their surfaces are more durable. The organic resins are moresensitive to small cracks because of various reasons such as low hardness andstrength, moisture sensitivity, tendency of porosity, sensitivity to moderate

temperature oxidation and ultraviolet radiation.

Another advantage of metal matrix alloys is their high thermal and electricalconductivity, which permits the diffusion and el imination of high thermal and electricalconcentrations. Problems such as lightning strikes and hot-gas impingement are lesssever if the impacting energy can be conducted away more rapidly.

Another important asset of metal matrices is their excellent reproducibility of theirmetal properties. This property is important not only for matrix alloy properties but

also the bonding and the interfacial properties.

Another important advantage of metal matrix alloys is the availability of an excellenttechnological background of their present use in the design of engineering structures,manufacturing techniques and a comprehensive information on service durability.

Although metal matrix composites have a lot of advantages, they have someimportant disadvantages. One of the most important disadvantages is that the metalmatrices are poor in chemical and mechanical compatibility with the reinforcements.In other words, the chemical inertness of the reinforcement (usually a fiber) atmodest resin-fabrication temperatures and large elastic compliance of the matrix arethe chemical and mechanical incompatibil ity problems.

Another reason of preference of resin-matrix composites is that the metal matrixcomposites are harder to fabricate then the resin-matrix composites.

To summarize; there are a lot of advantages of metal matrix composites over theother types but yet it has also some disadvantages too; so careful consideration mustbe given before preferring the metal matrices to the other types of compositematerials.

1.2 TYPES OF METAL MATRIX COMPOSITES

Metal matrix composites can be reinforced by strong second phases of three-dimensional shapes (particulate), two-dimensional shapes (laminar), or one-dimensional shapes (fibrous). All these three types differ in both the mechanicalproperties and the fabrication techniques.

1.2.1 Particle-Reinforced Composites

Particle reinforced composites although having a hard reinforcing dispersed phasediffer from the dispersion hardened materials in the sense that they have a highervolume fraction of dispersoid, smaller sizes of particles and interparticle spacing. With





par c e ase re n orce compos es suc as ungs en-car e-co a , e re n orc ngphase is the principal load-bearing phase and the matrix is used for transferring theload and for ease of fabrication. High matrix-constraint factors produced by the hardreinforcement are used to prevent yielding in the matrix and the composite strengthgenerally increases linearly with decreasing volume fraction of the matrix.

The three-dimensional reinforcement can lead to isotropic properties, since thematerial is symmetrical across the three orthogonal planes. Strength of theparticulate composites normally depends on the diameter of the particles,interparticle spacing and volume fraction of the reinforcement. Matrix properties,including the work-hardening coefficient, which increases the effectiveness of the

reinforcement constraint, are also important.

1.2.2 Laminated Composites

Laminated composite materials are considered to be reinforced by a repeating

lamellar reinforcement of high modulus and strength, which is contained in the moreductile and formable metal lic matrix material. Boron-carbide-titanium composites, inwhich the repeating reinforcing structural constituent consists of chemical-vapor-deposited boron carbide fi lms of 5-25mm thickness, can be an example of thelaminated composite materials; another kind of example can be the eutectoidcomposites of Ni-Mo and Al-Cu, in which two phases solidify in a lamellar array.

The elastic constants of a structural lamellar composite have been predicted by

laminate theory. In either of the directions of the reinforcing plates is given by therule of mixture:

EC = ERVR + EMVM

where ER, EM and EC are the elastic moduli of the reinforcement, matrix and composite

respectively, and V refers to the volume fraction.

The strength of laminated composite materials relate more closely to the propertiesof the bulk reinforcement. Since the reinforcing lamellae can have two dimensionsthat are comparable in size to the structural part, flaws in the reinforcement cannucleate cracks of lengths to that of the part. Since the most important reinforcingmaterials are brittle in nature, their strength is related to the population of their flawdensity and intensity.

The reinforcements of strength in all directions of the plane is a good advantage buttheir strength, elongation and ductility is lower than the fiber reinforced composites,since the corresponding values of films are lower than the values for fibers.

1.2.3 Fiber-Reinforced Composites

Generally these kinds of systems have relatively ductile low-yield-strength matricesand high-strength, high-modulus, brittle fibers.





Fig. 1.2. Schematic curve showing the stress-strain behavior of a metal-matrix composite: (I) fiber elastic, matrixelastic; (II) fiber elastic, matrix plastic; (III) fiber plastic, matrix plastic; (IV) fiber fractured.

When the metal-matrix composite with continuous uniaxially aligned fibers is stressedparallel to the fibers, four stages of stress-strain behavior is observed. In first stage,both the fiber and the matrix deforms elastically.

The elastic modulus has been found to be

EC = EFVF + EMVM

where V stands for volume fraction of the matrix M and the fiber F.

The second stage comprises the region in which the fiber is extending elastically andthe matrix is extending plastically. Since the fiber is usually in high volume fractionand has a considerably higher elastic modulus than the matrix, E2 is nearly equal toE1. The modulus of the composite would be the addition of the slopes on the stress-strain curve of the two phases t imes their volume fractions:

E11 = EFVF + (dsM /deM)

where dsM /deM is the effective strain-hardening coefficient of the matrix phase, which

is normally much less then the modulus of the fiber and can be neglected. Therefore,the modulus of the elastic-plastic portion of the stress-strain curve frequently can begiven as

E11 = EFVF The third stage is observed when both fiber and matrix can undergo plast ic

deformation and includes normal plastic extension of the two phases. Thisdeformation mode may deviate from the performance of the constituents alone with

respect to necking or other inhomogeneous plastic flow.

Forth stage in the stress-strain performance of the composite includes the fracturingof the high strength fibers. During this stage, the matrix transfers load from brokenfiber ends to unbroken segments and flows around the opening pores or cracks.Fracture of the composite normally terminates the forth stage.

The transverse or the shear properties of fiber-reinforced composite materials areconsiderably more influenced by the matrix behavior than the longitudinal propertiesare.

1.3 TYPES OF REINFORCEMENTS FOR METAL-MATRIXCOMPOSITES

Filamentary reinforcement has been found to make possible the most effectivereinforcement of metal matrix systems. These filaments used with three classes of





eng neer ng me a s: ow empera ure a oys suc as a um num a oys; n erme a etemperature alloys such as titanium and high temperature alloys such as nickel-basedsuperalloys or columbium alloys. Although the requirements of reinforcements changeas the matrix alloy is changed; there are some common properties such as:

High strength: necessary for composite strength and simplifies fabrication andhandling

High modulus: avoid extensive plastic matrix flowEase of fabrication and costChemical stabilitySize and shape of the fi lament: the larger diameter, circular for metal-matrix

composites for solid-state fabricationReproducibility or consistency of propertiesResistance to damage or abrasion

Rocket wire (steel), molybdenum and tungsten: high strength, ductility, excellenthigh temperature creep, but low modulus -to-density ratiosBeryllium: excellent modulus-to-density ratio, but high costE-glass and S-glass: excellent strength-to-density ratio, low cost, but low modulusand high chemical reactivityAluminum-oxide: single crystal, very high strength, but sensitive to abrasion andexpensiveSapphire: high temperature reinforcementBoron: excellent modulus-to-density and strength-to-density ratios, chemicalcompatibility with sol id aluminum and liquid magnesium, large diameter, reproducibleproperties and a competitive priceSilicon-carbide and boron-carbide: creep resistant but sensitive to abrasionGraphite: excellent modulus-to-density, strength-to-density ratios but chemicalreactive

1.4 MANUFACTURING TECHNIQUES OF METAL-MATRIXCOMPOSITES

These methods can be divided into 4 broad senses:

1. powder processes2. deposition processes3. liquid processes

4. solid state processes

Problems vary with the particular matrix-fiber combination being considered but atleast these three must always be kept in mind:

1. Reaction between fibers and matrix at elevated temperatures, either as thecomposite is being prepared or under service conditions

2. Obtaining sufficient bonding between the matrix and the fibers3. Alignment of fibers within the matrix

Powder Metallurgy: The powder metallurgy technique usually employs whiskers orcut fibers of the reinforcing materials. These are nixed with the matrix powder andthen pressed to consolidate the matrix. This may or may not be followed by sinteringto improve matrix density. A major problem when using powder metallurgy is theelimination of porosity. There is also difficulty in obtaining alignment of the

reinforcing material.





Fig. 1.3. Flowsheet for production of Composite of Titanium Reinforced w ith Molybdenum Fibers





Fig. 1.4. Microstructure of 15 Volume Percent Alumina in Beryllium (400X) )Courtesy of Aerospace Corp.)

Pneumatic Impaction: Pneumatic impaction can be considered as a variation of powder metallurgy since a powdered matrix is employed. The mixture of powder andreinforcing 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 andliquid process and also involves hot pressing. A layer of fibers is laid up on a rotatingmandrel, 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 thenumber of layers is attained.

Vapor Deposition: Vapor deposition is a process where the reinforcement, particularlywhiskers are coated by the matrix material from the deposition of its compounds.Extrusion process is finally employed for orienting the whiskers parallel to theextrusion axis.





Fig. 1.5. Heavy Vapor-plated SiC Whiskers, 1 to 5m, Bottom Surface of Mat (50X) (Courtesy of Melpar Inc.)

Electroforming: This process is especially used to prepare composites of boron inaluminum matrix. A continuous boron filament is on a mandrel is immersed in asolution. 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. Thecomposites were formed under vacuum by casting the matrix around the coatedfilaments.

Fig. 1.6. Cross -section of Boron Filament-Aluminum Matrix Samples Made by Liquid Infiltration (35X) (Courtesy of AVCO Corp.)

Fusion casting: There are two approaches of making a composite, which can beconsidered as a casting. In first method, a continuous reinforcing filament is fedthrough a pot of molten metal.





Fig. 1.7. Furnace for Application of Aluminum Coating to Steel Wire

The other way is the introduction of molten metal into, around and through mats orbundles of fibers or whiskers.

Fig. 1.8. Silicon Carbide Whiskers in M-45 Aluminum Alloy (150X)

Unidirectional Solidification of Eutectic Alloy: Another method of composite formation

is growth from a melt at certain temperatures and for some time ranges.

Fig. 1.9. Transverse Microstructure of Al3Ni-Al as a

function o f Solidification Rate (after George, Ford and

Fig. 1.10. Transverse Microstructure of Al3Ni-Al as a

function o f Solidification Rate (after George, Ford and





Sa n Sa n

Co-extrusion: Co-extrusion is a method that has been employed for the incorporationof continuous wires or fi laments to matrix. Since the matrix is worked by extrusion, itwill contribute appreciable strength to the composite.

Fig. 1.11. Design of Extrusion Tooling for Producing Composite Wire





Fig. 1.12. Extruded Aluminum-Steel Wire

Rolling: Hot or cold rolling can be employed to consolidate coated continuous fibers orto introduce continuous fibers or wires in matrix metal strips.

Fig. 1.13. Steel Wires Rolled into Aluminum Strip (100X)

Diffusion Bonding: In this method, alternate layers of matrix foil and properly spacedand oriented reinforcing fibers are laid down until the necessary amount of materialfor the desired final thickness is assembled. Then, by a combination of heat, pressureand time in a vacuum, the matrix is caused to flow around the fibers and bond to thenext layer of matrix and at the same t ime grip the reinforcing fiber very tightly.

Fig. 1.14. Boron-Aluminum Compos ite, 44 Volume Percent Boron Fiber, 0.004 Diameter (100X)

Contents:

1. Metal Matrix Composites 1.1 General Properties 1.2 Types Of Metal Matrix Composites

1.2.1 Particle-Reinforced Composites1.2.2 Laminated Composites1.2.3 Fiber-Reinforced Composites

1.3 Types Of Reinforcements For Metal-Matrix Composites 1.4 Manufacturing Techniques Of Metal-Matrix Composites

2. Ceramic Matrix Composite Materials

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2.2 Ceramic Matrix Composites 2.3 Applications Of Ceramic Matrix Composites 2.4 Processing Of Ceramic Matrix Composites

2.4.1 Processing Of Traditional Ceramics And Particulate Composites2.4.2 Processing Of Whisker And Short Fiber Reinforced Composites2.4.3 Processing Of Long Fiber Composites

Casting Equipmentwww.UltraflexPower.com

Induction Casting Machines. Pressure and Centrifugal Casting

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a literature survey study on metal and ceramic matrix composites_metal matrix composites

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