www.machinedesign.com Open in urlscan Pro
2606:4700::6812:1c4e  Public Scan

Form analysis
0 forms found in the DOM

Text Content

ResourcesMembersDirectoryWebinarsWISECAD ModelsAdvertise

 * 
 * Login
 * Join
 * Search

3D Printing & CADAUTOMATION & IIOTRoboticsMotion SystemsMaterialsVideoData
Sheets
Topics
Industry Markets3D Printing & CADAutomation & IIoTFastening &
JoiningMaterialsMechanical & Motion Systems Medical DesignRobotics
Resources
Machine Design ResourcesWISE (Workers in Science & Engineering)Company
DirectorySearch Data SheetsContributeDigital Edition ArchivesCSIA Exchange
Members
ContentBenefitsSubscribe
Advertise

https://www.facebook.com/MachineDesignMagazine/

https://www.linkedin.com/company/10998894

https://twitter.com/MachineDesign

https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg


    
 1. Materials
    


METAL-MATRIX COMPOSITES

Nov. 15, 2002

Metal-matrix composites are either in use or prototyping for the Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs,
and a variety of other applications.
 * 
 * 
   
 * 
 * 
 * 
 * 
   
   

Metal-matrix composites are either in use or prototyping for the Space Shuttle,
commercial airliners, electronic substrates, bicycles, automobiles, golf clubs,
and a variety of other applications. While the vast majority are aluminum matrix
composites, a growing number of applications require the matrix properties of
superalloys, titanium, copper, magnesium, or iron.

Like all composites, aluminum-matrix composites are not a single material but a
family of materials whose stiffness, strength, density, and thermal and
electrical properties can be tailored. The matrix alloy, the reinforcement
material, the volume and shape of the reinforcement, the location of the
reinforcement, and the fabrication method can all be varied to achieve required
properties. Regardless of the variations, however, aluminum composites offer the
advantage of low cost over most other MMCs. In addition, they offer excellent
thermal conductivity, high shear strength, excellent abrasion resistance,
high-temperature operation, nonflammability, minimal attack by fuels and
solvents, and the ability to be formed and treated on conventional equipment.

Aluminum MMCs are produced by casting, powder metallurgy, in situ development of
reinforcements, and foil-and-fiber pressing techniques. Consistently
high-quality products are now available in large quantities, with major
producers scaling up production and reducing prices. They are applied in brake
rotors, pistons, and other automotive components, as well as golf clubs,
bicycles, machinery components, electronic substrates, extruded angles and
channels, and a wide variety of other structural and electronic applications.



Superalloy composites reinforced with tungsten alloy fibers are being developed
for components in jet turbine engines that operate temperatures above 1,830 °F.

Graphite/copper composites have tailorable properties, are useful to high
temperatures in air, and provide excellent mechanical characteristics, as well
as high electrical and thermal conductivity. They offer easier processing as
compared with titanium, and lower density compared with steel. Ductile
superconductors have been fabricated with a matrix of copper and superconducting
filaments of niobium-titanium. Copper reinforced with tungsten particles or
aluminum oxide particles is used in heat sinks and electronic packaging.

Titanium reinforced with silicon carbide fibers is under development as skin
material for the National Aerospace Plane. Stainless steels, tool steels, and
Inconel are among the matrix materials reinforced with titanium carbide
particles and fabricated into draw-rings and other high-temperature,
corrosion-resistant components.




Compared to monolithic metals, MMCs have:

 * Higher strength-to-density ratios
 * Higher stiffness-to-density ratios
 * Better fatigue resistance
 * Better elevated temperature properties
   * -- Higher strength
   * -- Lower creep rate
 * Lower coefficients of thermal expansion
 * Better wear resistance

The advantages of MMCs over polymer matrix composites are:

 * Higher temperature capability
 * Fire resistance
 * Higher transverse stiffness and strength
 * No moisture absorption
 * Higher electrical and thermal conductivities
 * Better radiation resistance
 * No outgassing
 * Fabricability of whisker and particulate-reinforced MMCs with conventional
   metalworking equipment.

Some of the disadvantages of MMCs compared to monolithic metals and polymer
matrix composites are:

 * Higher cost of some material systems
 * Relatively immature technology
 * Complex fabrication methods for fiber-reinforced systems (except for casting)
 * Limited service experience

Numerous combinations of matrices and reinforcements have been tried since work
on MMC began in the late 1950s. However, MMC technology is still in the early
stages of development, and other important systems undoubtedly will emerge.

Reinforcements: MMC reinforcements can be divided into five major categories:
continuous fibers, discontinuous fibers, whiskers, particulates, and wires. With
the exception of wires, which are metals, reinforcements generally are ceramics.



Key continuous fibers include boron, graphite (carbon), alumina, and silicon
carbide. Boron fibers are made by chemical vapor deposition (CVD) of this
material on a tungsten core. Carbon cores have also been used. These relatively
thick monofilaments are available in 4.0, 5.6, and 8.0-mil diameters. To retard
reactions that can take place between boron and metals at high temperature,
fiber coatings of materials such as silicon carbide or boron carbide are
sometimes used.

Silicon carbide monofilaments are also made by a CVD process, using a tungsten
or carbon core. A Japanese multifilament yarn, designated as silicon carbide by
its manufacturer, is also commercially available. This material, however, made
by pyrolysis of organometallic precursor fibers, is far from pure silicon
carbide and its properties differ significantly from those of monofilament
silicon carbide.

Continuous alumina fibers are available from several suppliers. Chemical
compositions and properties of the various fibers are significantly different.
Graphite fibers are made from two precursor materials, polyacrilonitrile (PAN)
and petroleum pitch. Efforts to make graphite fibers from coal-based pitch are
under way. Graphite fibers with a wide range of strengths and moduli are
available.

The leading discontinuous fiber reinforcements at this time are alumina and
alumina-silica. Both originally were developed as insulating materials. The
major whisker material is silicon carbide. The leading U.S. commercial product
is made by pyrolysis of rice hulls. Silicon carbide and boron carbide, the key
particulate reinforcements, are obtained from the commercial abrasives industry.
Silicon carbide particulates are also produced as a by-product of the process
used to make whiskers of this material.



A number of metal wires including tungsten, beryllium, titanium, and molybdenum
have been used to reinforce metal matrices. Currently, the most important wire
reinforcements are tungsten wire in superalloys and superconducting materials
incorporating niobium-titanium and niobium-tin in a copper matrix. The
reinforcements cited above are the most important at this time. Many others have
been tried over the last few decades, and still others undoubtedly will be
developed in the future.

Matrix materials and key composites: Numerous metals have been used as matrices.
The most important have been aluminum, titanium, magnesium, and copper alloys
and superalloys.

The most important MMC systems are:


 * Aluminum matrix
   * Continuous fibers: boron, silicon carbide, alumina, graphite
   * Discontinuous fibers: alumina, alumina-silica
   * Whiskers: silicon carbide
   * Particulates: silicon carbide, boron carbide
 * Magnesium matrix
   * Continuous fibers: graphite, alumina
   * Whiskers: silicon carbide
   * Particulates: silicon carbide, boron carbide
 * Titanium matrix
   * Continuous fibers: silicon carbide, coated boron
   * Particulates: titanium carbide
 * Copper matrix
   * Continuous fibers: graphite, silicon carbide
   * Wires: niobium-titanium, niobium-tin
   * Particulates: silicon carbide, boron carbide, titanium carbide.
 * Superalloy matrices
   * Wires: tungsten

Characteristics and design considerations: The superior mechanical properties of
MMCs drive their use. An important characteristic of MMCs, however, and one they
share with other composites, is that by appropriate selection of matrix
materials, reinforcements, and layer orientations, it is possible to tailor the
properties of a component to meet the needs of a specific design.

For example, within broad limits, it is possible to specify strength and
stiffness in one direction, coefficient of expansion in another, and so forth.
This is rarely possible with monolithic materials.



Monolithic metals tend to be isotropic, that is, to have the same properties in
all directions. Some processes such as rolling, however, can impart anisotropy,
so that properties vary with direction. The stress-strain behavior of monolithic
metals is typically elastic-plastic. Most structural metals have considerable
ductility and fracture toughness.

The wide variety of MMCs have properties that differ dramatically. Factors
influencing their characteristics include:


 * Reinforcement properties, form, and geometric arrangement
 * Reinforcement volume fraction
 * Matrix properties, including effects of porosity
 * Reinforcement-matrix interface properties
 * Residual stresses arising from the thermal and mechanical history of the
   composite
 * Possible degradation of the reinforcement resulting from chemical reactions
   at high temperatures, and mechanical damage from processing, impact, etc.

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.

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.

MMCs reinforced with aligned fibers have anisotropic properties. They are
stronger and stiffer in the direction of the fibers than perpendicular to them.
The transverse strength and stiffness of unidirectional MMCs (materials having
all fibers oriented parallel to one axis), however, are frequently great enough
for use in components such as stiffeners and struts. This is one of the major
advantages of MMCs over PMCs, which can rarely be used without transverse
reinforcement.



Because the modulus and strength of metal matrices are significant with respect
to those of most reinforcing fibers, their contribution to composite behavior is
important. The stress-strain curves of MMCs often show significant nonlinearity
resulting from yielding of the matrix.

Another factor that has a significant effect on the behavior of fiber-reinforced
metals is the frequently large difference in coefficient of expansion between
the two constituents. This can cause large residual stresses in composites when
they are subjected to significant temperature changes. In fact, during cool down
from processing temperatures, matrix thermal stresses are often severe enough to
cause yielding. Large residual stresses can also be produced by mechanical
loading.

Although fibrous MMCs may have stress-strain curves displaying some
nonlinearity, they are essentially brittle materials, as are PMCs. In the
absence of ductility to reduce stress concentrations, joint design becomes a
critical design consideration. Numerous methods of joining MMCs have been
developed, including metallurgical and polymeric bonding and mechanical
fasteners.

Fabrication methods: 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.
Primary fabrication methods are used to create the MMC from its constituents.
The resulting material may be in a form that is close to the desired final
configuration, or it may require considerable additional processing, called
secondary fabrication, such as forming, rolling, metallurgical bonding, and
machining. The processes used depend on the type of reinforcement and matrix.

A critical consideration is reactions that can occur between reinforcements and
matrices during primary and secondary processing at the high temperatures
required to melt and form metals. These impose limitations on the kinds of
constituents that can be combined by the various processes. Sometimes, barrier
coatings can be successfully applied to reinforcements, allowing them to be
combined with matrices that otherwise would be too reactive. For example, the
application of a coating such as boron carbide permits the use of boron fibers
to reinforce titanium. Potential reactions between matrices and reinforcements,
even coated ones, is also an important criterion in evaluating the temperatures
and corresponding lengths of time to which MMCs may be subjected in service.

Relatively large-diameter monofilament fibers, such as boron and silicon
carbide, have been incorporated into metal matrices by hot pressing a layer of
parallel fibers between foils to create a monolayer tape. In this operation, the
metal flows around the fibers and diffusion bonding occurs. The same procedure
can be used to produce diffusion-bonded laminates with layers of fibers oriented
in specified directions to meet stiffness and strength requirements for a
particular design. In some instances, laminates are produced by hot pressing
monolayer tapes in what can be considered a secondary operation.

Monolayer tapes are also produced by spraying metal plasmas on collimated
fibers, followed by hot pressing. Structural shapes can be fabricated by creep
and superplastic forming of laminates in a die. An alternate process is to place
fibers and unbonded foils in a die and hot press the assembly.



The boron/aluminum struts used on the space shuttle are fabricated from
monolayer foils wrapped around a mandrel and hot isostatically pressed to
diffusion bond the foil layers together and, at the same time, to diffusion bond
the composite laminate to titanium end fittings.

Composites can be made by infiltrating liquid metal into a fabric or prearranged
fibrous configuration called a preform. Frequently, ceramic or organic binder
materials are used to hold the fibers in position. The latter is burned off
before or during infiltration. Infiltration can be carried out under vacuum,
pressure, or both. Pressure infiltration, which promotes wetting of the fibers
by the matrix and reduces porosity, is often called squeeze casting.



Cast MMCs now consistently offer net or net-net shape, improved stiffness and
strength, and compatibility with conventional manufacturing techniques. They are
also consistently lower in cost than those produced by other methods, are
available from a wide range of fabricators, and offer dimensional stability in
both large and small parts.

For example, Duralcan has developed its "ice cream mixer" technology and process
controls to the point where it produces up to 25 million pounds per year of
aluminum composite billets. Investment casting has been modified at Cercast to
cast Duralcan billets into complex, net-shape parts. Pressure casting produces
net shapes with exceptional properties at Alcoa, while pressureless infiltration
is used at Lanxide Corp. to fabricate net-shape components.

At the current time, the most common method used to make graphite/aluminum and
graphite/magnesium composites is by infiltration. Graphite yarn is first passed
through a furnace to burn off any sizing that may have been applied. Next it
goes through a CVD process that applies a coating of titanium and boron which
promotes wetting by the matrix. Then it immediately passes through a bath or
fountain of molten metal, producing an infiltrated bundle of fibers known as a
"wire." Plates and other structural shapes are produced in a secondary operation
by placing the wires between foils and pressing them, as is done with
monofilaments. Recent development of "air stable" coatings permits use of other
infiltration processes, such as casting, eliminating the need for "wires" as an
intermediate step. Other approaches are under development.

A particularly important secondary fabrication method for titanium matrix
composites is superplastic forming/diffusion bonding (SPF/DB). To reduce
fabrication costs, continuous processes such as pultrusion and hot roll bonding
are being developed.

Three basic methods are being used to make whisker and particulate-reinforced
MMCs. Two use powdered metals; the other uses a liquid-metal approach, details
of which are proprietary.

The two powder-metal processes differ primarily in the way the constituents are
mixed. One uses a ball mill, the other employs a liquid to aid mixing, which is
subsequently removed. Mixtures are then hot pressed into billets.

Secondary processes are similar to those for monolithic metals, including
rolling, extrusion, spinning, forging, creep-forming, and machining. The latter
poses some difficulties because the reinforcements are very hard.




CONTINUE READING

Q&A: EXPLORING THE FUTURE OF MULTI-MATERIAL 3D PRINTING


5 COMMON MACHINING MISTAKES TO AVOID


SPONSORED RECOMMENDATIONS

SCHMERSAL PRODUCT DEMO: SLC BLE

Oct. 31, 2023

SAFETY LIGHT CURTAIN ALIGNMENT 101

Oct. 31, 2023

SCHMERSAL ON MACHINE SAFETY: MANUAL RESET

Oct. 31, 2023

PLEASE UPDATE YOUR BROWSER

Oct. 31, 2023

VOICE YOUR OPINION!


TO JOIN THE CONVERSATION, AND BECOME AN EXCLUSIVE MEMBER OF MACHINE DESIGN,
CREATE AN ACCOUNT TODAY!

Join today!
I already have an account


NEW

R&D SPOTLIGHT: INVENTING WEARABLE SENSORS THAT MONITOR URIC ACID IN SWEAT


FAQ: WHY SHOULD YOU INCORPORATE PUSH-IN TERMINALS IN YOUR NEXT DIN RAIL
APPLICATION?


THE DIFFERENCE BETWEEN: BALL SCREW ACTUATORS AND BALL SCREW SPLINES


MOST READ

WHY IT’S TIME TO REPLACE HYDRAULIC AND PNEUMATIC ACTUATORS WITH ELECTRIC
CYLINDERS


HOW MUCH SHOULD A BOLTED JOINT BE TIGHTENED?


2023 IDEA AWARDS: SITIME IS THE BIG IDEA WINNER



SPONSORED

COMMUNICATION, PREDICTIVE MAINTENANCE, AND SAFETY.


KEYED SOLENOID LOCKING SAFETY SWITCHES


CAPACITIVE SENSORS



Loading Content


https://www.facebook.com/MachineDesignMagazine/

https://www.linkedin.com/company/10998894

https://twitter.com/MachineDesign

https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg

   
 * About Us
 * Contact Us
 * Advertise
 * Do Not Sell or Share
 * Privacy & Cookie Policy
 * Terms of Service
   

© 2023 Endeavor Business Media, LLC. All rights reserved.


This website uses cookies to enhance your browsing experience and serve
personalized content.Privacy Policy

Accept All



PRIVACY PREFERENCE CENTER

When you visit any website, it may store or retrieve information on your
browser, mostly in the form of cookies. This information might be about you,
your preferences or your device and is mostly used to make the site work as you
expect it to. The information does not usually directly identify you, but it can
give you a more personalized web experience. Because we respect your right to
privacy, you can choose not to allow some types of cookies. Click on the
different category headings to find out more and change our default settings.
However, blocking some types of cookies may impact your experience of the site
and the services we are able to offer.
More information
Allow All


MANAGE CONSENT PREFERENCES

STRICTLY NECESSARY COOKIES

Always Active

These cookies are necessary for the website to function and cannot be switched
off in our systems. They are usually only set in response to actions made by you
which amount to a request for services, such as setting your privacy
preferences, logging in or filling in forms. You can set your browser to block
or alert you about these cookies, but some parts of the site will not then work.
These cookies do not store any personally identifiable information.

STATISTICAL COOKIES

Always Active

These cookies allow us to count visits and traffic sources so we can measure and
improve the performance of our site. They help us to know which pages are the
most and least popular and see how visitors move around the site. These cookies
generate aggregate statistics that are not associated with an individualized
profile. If you do not allow these cookies we will not know when you have
visited our site, and will not be able to monitor and improve its performance.

FUNCTIONALITY COOKIES

Always Active

These cookies enable the website to provide enhanced functionality and
personalisation. By recognizing you when you return to our website, these
cookies allow us to record information about your visit to our website, such as
pages visited, links followed, and videos viewed so we can personalize our
content for you, remember your preferences (for example, your choice of topics,
language or region), and display advertising that is more relevant to your
interests. These cookies may enable visitor identification over time, but not
across non-Endeavor Business Media websites. They may be set by us or by third
party providers whose services we have added to our pages. If you do not allow
these cookies then some or all of these services may not function properly.

THIRD PARTY ADVERTISING COOKIES

Always Active

These cookies may be set through our site by third party advertisers. They may
be used by those companies to build a profile of your interests and show you
relevant advertisements on other sites. These cookies may enable visitor
identification across websites and over time. They are based on uniquely
identifying your browser and internet device. We do not control the third
party's use of those cookies, their duration, or their ability to share
information with other third parties. Please review each party's cookie
disclosure before consenting to this use category.

Back Button


PERFORMANCE COOKIES



Search Icon
Filter Icon

Clear
checkbox label label
Apply Cancel
Consent Leg.Interest
checkbox label label
checkbox label label
checkbox label label

Confirm My Choices


Most Popular

Supply Chain Resources

 * Smith & Associates Opens Sales Office in Bangalore
 * Electronics Distributors Outlook for 2021
 * To Buy or Not to Buy From Independent Distributors

Powered by: