1. Metallic Glasses

2. CRYSTAL Regular atomic arrangements. Slip planes for
Plastic deformation.
Metals and alloys are
naturally crystalline.
Have high strength
and low hardness.

3. GLASS No periodic arrangement. Density same as crystal.
Have high hardness.
Plastic flow is difficult.

4. CRYSTAL GLASS METALLIC GLASS High strength High hardness Low hardness
Quasi brittle fracture (at room temperature)

5. METALLIC GLASSES (AMORPHOUS METAL)
An Amorphous metal is a metallic material with a disordered atomic scale structure.
Formed by rapid cooling of metallic liquids.
Have disordered structure just like glass and composed of metallic atoms.
Much harder than any glass and twice as strong as an alloy like stainless steel.

6. HOW TO MAKE A GLASS
A glass is formed by avoiding crystallization on cooling.
To avoid crystallization rapid cooling is done directly from
liquid state.
The density of glass depends upon the cooling rate.
Pure metals does not form glasses their structure crystallizes on
cooling the liquid when cooling is done at a slow rate.

7. History
In 1957 Pol Duweg produced first metallic glass alloy (Au80Si20) at
Caltech, these alloys had to be cooled rapidly(106 Ks-1) to avoid crystallization.
In 1976 H. Liebermann and C. Graham manufactured Metglas which is an
alloy of iron , nickel, phosphorous and boron.
The research in Tohoku University and Caltech yielded multicomponent
alloys based on lanthanum, magnesium, zirconium, palladium, iron, copper and
titanium with cooling rate between 1Ks-1 – 100Ks-1
Many amorphous alloys are formed by exploiting a phenomenon called the “Confusion Effect”

8. CONFUSION EFFECT WHAT IS THIS
We know that the metallic glass is an alloy of different elements (often a dozen or more) that upon cooling at faster rates the constituent atoms does not coordinate themselves into equilibrium crystalline state before
there mobility is stopped and in this manner the random disordered
state of the atoms is “locked in”.

9. Methods The various methods to produce amorphous alloys are:
Physical vapour deposition
Melt spinning
Suction casting
Solid state reaction

10. Physical vapour deposition
Source material gets heated up in the tube furnace and forms vapours.
The vapours are carried by the carrying gas and are made to get
deposited on the substrate.
The vapours get deposited on the substrate in the form of a disordered
atomic scale structure.
Hence the name given as physical vapour deposition and the vapours
deposited on the substrate will solidify to form the glassy structure.

11. Single roller melt spinning
In this process, the alloy is melted (typically in a quartz tube) by induction heating.
Then it is forced out through a narrow nozzle onto the edge of a rapidly rotating chill wheel(usually made up of copper)

12. Single roller melt spinning (cont..)
At least one dimension must be very small, so that heat can be extracted quickly enough to achieve the necessary cooling rate.
As a result, the early glass-forming alloys could only be produced as thin ribbons (typically around 50 μm thick), wires, foils, or powders.

13. Suction Casting
An ingot in the upper chamber under an inert atmosphere is melted with an electric arc (much like in arc welding) and then sucked into a mold when the lower chamber is opened to vacuum.
One of the potentially useful properties of metallic glasses is that they do not melt abruptly at a fixed temperature.

14. Suction casting (cont..)
Instead, like ordinary oxide glasses, they gradually soften and flow over a range of temperatures.
By careful control of temperature, the viscosity of the softened glass can be precisely controlled.
This ability can be used to form metallic glasses into complex shapes

15. Properties Alloys rather than metals. Low free volume.
High viscosity, low shrinkage and resistance to plastic deformation.
Better resistance to wear and corrosion due to absence of grain boundaries.
Thermal conductivity lower than crystals.
They are not ductile in room temperature and tends to fail suddenly when loaded in tension ( quassi brittle fracture )
Therefore, they are bombarded with high energy ions in order to make them ductile in nature.

16. Amorphous metallic alloys combine higher strength than crystalline
metal alloys with the elasticity of polymers

17. VITRELOY Vitreloy was the first commercial amorphous alloy in 1992.
Developed at Caltech as a part of Department of Energy and NASA research of new aerospace materials.
Tensile strength that is almost twice that of high grade titanium.

18. Applications
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 on substances via high velocity oxygen fuel technique as protective coatings.
Used in injection moulding since they melt and soften over a range of temperature.
They are used in producing various complex shapes.

19. Equipments

20. Why metallic glasses is used as one of the component in
Sports equipment
Consider an experiment
where in you have two
cylindrical tubes.
One is covered with a metal
at the bottom and the other
with a metallic glass.
A ball bearing is made to
fall on both the metal
and glass surface.

21. Conclusions from the experiment
From the experiment we can conclude that
The energy transmitted by the ball bearing to the titanium metal is more
which is the reason why it bounces to a small altitude and comes to rest.
The energy transmitted by the ball bearing to the liquid metal alloy is less
so as a result it keeps on bouncing at a fixed height for a longer period
of time.
This is the reason why golf sticks and other sports equipments are made
with metallic glass material so that the energy transferred from the ball
to the stick is less which enables the ball to travel greater distances.

22. Observations from the experiments
The ball bearing when it falls on
the titanium metal, we observe
that the ball will come to rest
after a span of around 3-4 seconds.
But when the ball falls on the liquid
metal alloy we observe that the ball
keeps on bouncing at a constant
height for certain period of time say
about 8-10 seconds.

23. 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 done.
Common oxide glasses are quite resistance to crystallization so they can be formed even if the liquid is cooled very slowly.
The earliest metallic glasses (discovered at Caltech in 1950) required rapid cooling around 1 million degrees celsius per second to avoid crystallization.

24. Processing of Metallic Glasses (cont..)

25. Bombardment of high energy ions
The kinetic energy of high energy ions will make the atomic structure
present in the glass to reorient themselves in such a manner that
they become ductile in nature.

26. References
[1] htm
[2] M. Telford, Materials Today, March 2004, 36-43
[3]
[4] tml
[5]
[6]
[7]
[8] W.H. Wang, C. Doug, C.H. SHek, Materials Science and Engineering, R44 (2004), 45-89