metalic glasses,comparision with crystaline alloys,properties,applications are in brief

1. Subject : Advanced
Material
Topic:Metallic glasses,
Comparison with crystalline
alloys, properties &
applications
1

2. AMORPHOUS METAL
An amorphous metal is a metallic material
with a disordered atomic-scale structure. In
contrast to most metals, which are
crystalline and therefore have a highly
ordered arrangement of atoms, amorphous
alloys are non-crystalline.
amorphous
crystalline
Materials in which such a disordered
structure is produced directly from the
liquid state during cooling are called
"glasses", and so amorphous metals are
commonly referred to as "metallic glasses"
or "glassy metals".

3. 3
1. Conventional metallic glass
• Glass is a uniform amorphous solid material, usually produced
when the viscous molten material cools very rapidly to below its
glass transition temperature, without sufficient time for a regular
crystal lattice to form. The term glass transition refers to the
enormous slowing down in the dynamics of some liquids when
their temperature is lower.
• Amorphous materials are often prepared by rapidly cooling molten
material.
• The cooling reduces the mobility of the material's molecules before
they can pack into a more thermodynamically favorable crystalline
state. Amorphous materials can also be produced by additives
which interfere with the ability of the primary constituent to
crystallize.
• For example addition of soda to silicon dioxide results in window
glass.

4. 4
Figure 1: The atomic structure of
conventional metal.
Figure 2: An amorphous atomic structure.
• The atomic structure is the most striking
characteristic of the liquid metal alloys as
it fundamentally differentiates liquid
metal alloys from ordinary metals.
• Liquid metal alloys possess an amorphous
atomic structure, which is truly unique
(Figure 1 and Figure 2).

5. 5
Figure 3: Typical strengths and elastic limit for
various materials.

6. PROCESSING OF METALLIC GLASSES
Virtually any liquid can be turned into a glass if it is cooled quickly enough
to avoid crystallization. The question is, how fast does the cooling need to
be?
Common oxide glasses (such as ordinary window glass) are quite resistant
to crystallization, so they can be formed even if the liquid is cooled very
slowly. For instance, the mirror for the 200" telescope at the Palomar
Observatory weighed 20 tons and was cooled over a period of eight
months, but did not crystallize.
Many polymer liquids can also be turned into glasses; in fact, many
polymers cannot be crystallized at all.
For both oxides and polymers, the key to glass formation is that the liquid
structure cannot be rearranged to the more ordered crystalline structure in
the time available.

7. PROCESSING OF METALLIC GLASSES

8. PROPERTIES
Perhaps the most useful property of bulk amorphous alloys is that they are
true glasses, which means that they soften and flow upon heating. This
allows for easy processing, such as by injection molding, in much the same
way as polymers.
As a result, amorphous alloys have been commercialized for use in sports
equipment, medical devices, and as cases for electronic equipment.
Thin films of amorphous metals can be deposited via high velocity oxygen
fuel technique as protective coatings.

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Comparison of properties of metals, glasses
and metallic glasses
Properties Traditional metal Traditional glass Metallic glass
Structure Crystalline Amorphous Amorphous
Bonding Metallic Covalent Metallic
Yield stress Non-ideal Almost ideal Almost ideal
Workability Good, ductile Poor, brittle Good, ductile
Hardness Low to high Very high Very high
Thermal
conductivity
Very good Poor Very good
Resistance Very low High High
Corrosion
Oxidation
resistance
/ Poor to good Very good Very good

10. 10
Applications
• In making stiff knifes for cutting various articles
• Tape-recorder/video cassette recorder heads
• Sports equipment: BMG are used in making of the golf club head (high
strength and toughness)
• Transformer core materials (low losses by eddy currents)
• As biomaterials for example, in artificial joints, bone plates, artificial
tooth roots, sensors of pace maker etc;
• As protective coatings: Thin films of amorphous metals can be deposited
via high velocity oxygen fuel technique.
• As cases for electronic equipment.

11. Reference by:
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[1]http://www.sciencedaily.com/releases/1998/03/980331074950.
htm
[2] M. Telford, Materials Today, March 2004, 36-43
[3] http://www.its.caltech.edu/~vitreloy/development.htm
[4]http://www.nanonet.go.jp/english/mailmag/2004/014a.html
[5] http://en.wikipedia.org/wiki/Metallic_Glass#Properties
[6] http://science.nasa.gov/ssl/msad/dtf/under1.htm
[7] http://www.liquidmetal.com/technology/
[8] W.H. Wang, C. Doug, C.H. SHek, Materials Science and
Engineering, R44 (2004), 45-89

12. THANK YOU
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