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Metal Matrix Composites

Mechanics of Composites (ME 4129)

Content

Introduction

Characteristics & Advantages

Classification

Stress-Strain Curve

Manufacturing Techniques

Applications

Definition A metal matrix composite (MMC) is composite

material having at least two constituent as metal necessarily, however the other material may be a different metal or another material, such as a ceramic or organic compound.

A Hybrid composite is one where number of constituents materials are at least three.

An analogy of Metal matrix composite (MMC) can be drawn to cement.

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Characteristics

Better strength and low creep at higher temperature

Excellent Fatigue Resistance

Higher strength, stiffness to mass density ratio

Low coefficient of thermal expansion

Better wear resistance

2

Advantages Higher Electrical and Thermal Conductivities

Better radiation resistance

Higher temperature capability

Fire resistance

No outgassing

Fabricability of whisker and particulate-reinforced MMCs with conventional metalworking equipment.

Higher transverse stiffness and strength

3

Disadvantages

Complex fabrication methods for fiber-reinforced

systems (except for casting)

Relatively immature technology

Higher cost of some material systems

Limited service experience

4

Reinforcements for MMC

MMC reinforcements can be divided into five major categories:

Continuous fibers

Discontinuous fibers

Whiskers

Particulates

Wires

Note: With the exception of wires, which are metals, reinforcements generally are ceramics.

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Continuous fibers-Boron It includes boron, graphite (carbon), alumina, and silicon

carbide (SiC).

Boron fibers are made by chemical vapor deposition

(CVD) of this material on a tungsten core.

To retard reactions that can take place between boron and

metals at high temperature, fiber coatings of mat are used.

Carbon cores have also been used. These relatively thick

monofilaments are available in 4.0, 5.6, and 8.0-mil dia.

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Silicon carbide monofilaments are also made by a CVD process, using a tungsten or carbon core

A Japanese multifilament yarn, designated as SiC by its manufacturer, is also commercially available

The above material is made by pyrolysis of

organometallic precursor fibers

The Japanese multifilament yarn has its properties significantly different from monofilament SiC.

Continuous fibers- SiC Monofilaments

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Graphite fibers are made from two precursor

materials, polyacrilonitrile (PAN) and petroleum.

The Resesarch is under way for manufact. of coal-

based graphite fibre.

Graphite fibers with a wide range of strengths and

moduli are available.

Continuous fibers- Graphite

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The leading discontinuous fiber reinforcements are

alumina and alumina-silica.

The major whisker material is silicon carbide.

SiC and boron carbide, are obtained from the

commercial abrasives industry.

SiC particulates are also produced as a by-product of

the process used to make whiskers of this material.

Discontinuous fibers, Whisker, Particulates

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Popular MMC Configurations

Aluminium Matrix Based

Continuous fibers: boron, silicon carbide, alumina,

graphite

Discontinuous fibers: alumina, alumina-silica

Whiskers: silicon carbide

Particulates: silicon carbide, boron carbide

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Popular MMC Configurations

Magnesium Matrix Based

Continuous fibers: graphite, alumina

Whiskers: silicon carbide

Particulates: silicon carbide, boron carbide

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Popular MMC Configurations Titanium Matrix Based

Continuous fibers: silicon carbide, coated boron

Particulates: titanium carbide

Copper Matrix Based

Continuous fibers: graphite, silicon carbide

Wires: niobium-titanium, niobium-tin

Particulates: Sic, boron carbide, titanium carbide.

Superalloy matrices Based

Wires: tungsten

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Disadvantages

Higher cost of some material systems

Relatively immature technology

Complex fabrication methods for fiber-reinforced

systems (except for casting)

Limited service experience

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Factors influencing MMC characteristics

Reinforcement properties, form, and geometric

arrangement

Reinforcement volume fraction

Matrix properties, including effects of porosity

Reinforcement-matrix interface properties

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Residual stresses arising from the thermal and

mechanical history of the composite

Possible degradation of the reinforcement resulting

from chemical reactions at high temperatures

Mechanical damage from processing, impact, etc.

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Particulate-reinforced MMCs, like monolithic metals, tend to be isotropic.

The presence of brittle reinforcements and perhaps of metal oxides, however, tends to reduce their ductility and fracture toughness.

Continuing development may reduce some of these deficiencies.

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The properties of materials reinforced with whiskers

depend strongly on their orientation.

Randomly oriented whiskers produce an isotropic

material.

Processes such as extrusion can orient whiskers,

however, resulting in anisotropic properties.

Whiskers also reduce ductility and fracture toughness.

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Stress-Strain Curve

Stage I : Both Matrix

and Fiber remain elastic

Stage II : Matrix

deforms plastically and

Fiber remain elastic

Stage III : Both Matrix

and Fibre deforms

plastically

Source: Taya, M. (1991) “Mat. Trasc” 32, 1-19

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Manufacturing Techniques

Powder Metallurgy

Liquid metallurgy

Secondary Processing

Special Fabrication

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Powder Metallurgy Def. 1:

It is the process by which fine powder are blended pressed to desired shape (compacted), and then heated (sintered) in a controlled atmosphere to bond contacting surface of particles and establish desire properties.

Def. 2:

It may be defined as material processing technique used to consolidate particulate matter i.e. powder both metal and non-metal

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Powder production:

Powder Metallurgy Process

Atomization: Stainless steel, nickel alloy and titanium alloy

powder can be produced by this method

Chemical Reduction: Powders like iron, copper, tungsten and

molybdenum can be produced by this method

Electrolytic Deposition: Powders like iron, copper and silver

can be produced by this method

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Blending : It is the method in where powders of the

equal minimal composition but having various

particle sizes and shapes are combined.

Compaction: It is the process of compacting metal

powder in a die through the application of high

pressures.

Sintering:


It is a heat treatment applied to a powder compact in order to impart

strength and integrity.

It is a heat treatment applied to a powder compact in order to impart

strength and integrity. 22


Source: Tripathy et al. (2018), Int. J. Engg.& Tech., 7, 1-5 23

Powder Metallurgy: Advantages A variety of metal or non metal powders can be used.

Refractory materials are easily processed

Economical for mass production

Very good material utilization

Minimization or elimination of Machining

24

Powder Metallurgy: Limitations

Initial Investment cost high

Limited part size and complexity

High cost of powder material

High cost of tooling

Health hazard to the operator due to very fine powder

25

Liquid Metallurgy

It involves incorporation of dispersed phase into a

molten matrix metal, followed by its Solidification.

A good interfacial bonding (wetting) between the dispersed

phase and the liquid matrix should be obtained.

Wetting improvement may be achieved by coating the

dispersed phase particles (fibers).

Proper coating prevents chemical interaction between the

dispersed phase and the matrix. 26

Liquid Met.: Processing Techniques

Stir Casting

Infiltration

Gas Pressure Infiltration

Squeeze casting Infiltration

Pressure Die Infiltration

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Stir Casting : It is a liquid state method of composite materials

fabrication, in which a dispersed phase is mixed

with a molten matrix metal by means of

mechanical stirring.

It is the simplest and the most cost effective

method of liquid state fabrication.

Characteristics: Content of dispersed phase is limited

Distribution of dispersed phase throughout the

matrix is not perfectly homogeneous

Distribution of dispersed phase may be improved

if the matrix is in semi-solid condition. 28


Infiltration : It is a liquid state method of composite materials

fabrication, in which dispersed phase is soaked in

a molten matrix metal, which fills the space

between the dispersed phase inclusions.

The motive force of an infiltration process may

be either capillary force of the dispersed phase or

an external pressure

It is one of methods of preparation of tungsten-

copper composites.

29


Steps in Infiltration :

Tungsten Powder preparation with average particle

size of about 1-5 μm.

Mixing the tungsten powder with a polymer binder.

Compacting the powder by a molding method.

It is the green compact at 2200-2400F

Placing the sintered part on a copper plate in the sintering

fur. 30


Gas Pressure Infiltration

In this method a pressurized gas for applying pressure on the

molten metal and forcing it to penetrate into a preformed

dispersed phase.

Gas Pressure Infiltration method is used for manufacturing

large composite parts.

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Squeeze Casting Infiltration

It uses a movable mold part (ram) for applying pressure on the

molten metal and forcing it to penetrate into a performed

dispersed phase, placed into the lower fixed mold part.

Steps in Squeeze Casting

Dispersed phase is placed into the lower fixed mold half.

A molten metal in a predetermined amount is poured into the

lower mold half.

The upper movable mold half (ram) moves downwards and

forces the liquid metal to infiltrate the preform.

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Steps in Squeeze Casting

The infiltrated material solidifies under the pressure.

The part is removed from the mold by means of the ejector pin.

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Liquid Met.: Processing Techniques Pressure Die Infiltration

It is a forced infiltration method of liquid phase fabrication of

Metal Matrix Composites, using a Die casting technology.

Dispersed phase is placed into a die (mold) which is then filled

with a molten metal entering the die through a sprue and

penetrating into liquid under the pressure of a movable piston

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Special Fabrication Technique

It is a process, in which dispersed phase is formed in

the matrix as a result of precipitation from the melt during its

cooling and Solidification.

Different types of Metal Matrix Composites may be prepared

by in situ fabrication method:

Particulate in situ MMC: Particulate composite reinforced by in situ

synthesized dispersed phase in form of particles

Short-fiber reinforced in

situ MMC:

It is reinforced by in situ synthesized dispersed

phase in form of short fibers or whiskers

Long-fiber reinforced in

situ MMC:

It is reinforced by in situ synthesized dispersed

phase in form of continuous fibers.

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Special Fabrication Technique : In situ MMC

Unidirectional solidification of a eutectic

alloy results in formation of eutectic

structure, in which one of the components

has a form of long continuous filaments.

Crucible with an eutectic alloy moves

downwards This movement results in

remelting followed by resolidification of the

alloy under controlled cooling conditions.

Value of heat transfer through the crucible

bottom together with the crucible speed (v)

and the power of the heating elements

determine particular temperature gradient.

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Advantages of In situ MMC Here particles and fibers are smaller than those in materials with

separate fabrication of dispersed phase. Fine particles provide

better strengthening effect.

In situ fabrication provides more homogeneous distribution of

the dispersed phase particles

Bonding between the particles of in situ formed dispersed

phase and the matrix is better than in ex-situ MMCs

Equipment and technologies for in situ fabrication of MMCs

are less expensive.

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Disadvantages of In situ MMC Choice of the dispersed phases is limited by thermodynamic

ability of their precipitation in particular matrix;

The size of dispersed phase particles is determined by

solidification conditions.

Not a conventional method and mass production may be slower

Experience operator is required to handle intricate shapes

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Application of MMC

Manufacturing of High performance tungsten

carbide cutting tools.

Some tank armors may be made from metal matrix

composites.

Some automotive disc brakes are manufactured using

MMCs.

The MMC driveshaft is made of an aluminum matrix

reinforced with boron carbide. 39

Application of MMC

Honda has used aluminum metal matrix composite

cylinder liners in some of their engines

Toyota has since used metal matrix composites in

the Yamaha-designed 2ZZ-GE engine

The F-16 Fighting Falcon uses monofilament silicon

carbide fibers in a titanium matrix for a structural

component of the jet's landing gear.

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Application of MMC

Specialized Bicycles has used aluminum MMC

compounds for its top of the range bicycle frames for

several years.

Some equipment in particle accelerators such as Radio

Frequency Quadrupoles (RFQs) or electron targets use

copper MMC compounds.

Copper-silver alloy matrix containing 55% by

volume diamond particles, known as Dymalloy, is used

as a substrate for high-power.

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Future Application

Nanotechnology

Aerospace Application

Bearing up under pressure

Piston, Cylinders and Brakes

Self Healing Material

42

Thank You

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