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Metallic Glasses in Cell Phones
Angelika Franz
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Outline
• what is a metallic glass
• structure
• properties
• processing
• cell phone cases
• cell phone hinges
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Metallic Glass I
• amorphous material: atoms “frozen” in non-crystalline form
• lack long-range atomic order
• first formed in 1957 by Duwez by rapid quenching gold-silicon alloy only very thin, small samples could
be produced (order or micrometers)
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Metallic Glass II
• 1990: found new alloys to form bulk metallic glasses typically used three or more
metallic elements
• cooling rates needed decreased
• could produce samples on order of centimetersZr-Ti-Cu-Ni-Al alloy
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Structure I
• first believed atoms were randomly packed together densly like hard spheres in a liquid solvent atoms randomly arranged with solute
atoms fitting into open cavities
• now believe short-range, even medium-range order exists in materials
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Structure II
• form nanoscale “superclusters” difference in size between alloyed elements make
solvent atoms cluster around solute atoms Kasper polyhedra: 7 to 15 atoms arranged around
central atom polyhedra shape depends on size of constituent atoms range of coordination numbers: different polyhedra
exist within same material
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Structure III
• was proposed that clusters conform to fcc lattice for closest-packing with strain factor to limit order to 1-1.5 nm
• actually found clusters pack into icosahedral structures usually 1.5 nm wide creates cavities into which extra solute atoms
can pack
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Properties I
• lack of crystallinity means lack of defects gives rise to interesting properties
• stronger and lighter than metals
• tough: resistant to fracture unlike ceramic glass is not brittle
• easily heated, softened and molded into shapes
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Properties II
• uncorrosive
• not transparent
• very high elastic strain limit makes material bouncy
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Processing I
• formed by quenching at rates of 1-100 degrees Celsius per second used to be 1 million degrees Celsius per
second
• prevent atoms from forming into crystalline structure, instead freeze into liquid-like structure
• limits size and shape of material produced
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Processing II
• near net-shape casting alloy is cast near to final shape
• injection molding metallic glass is heated until it softens and can
flow into the mold
• physical vapor deposition
• ion irradiation
• mechanical alloying
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Cell Phone Cases I
• alloy of zirconium, titanium, copper, nickel and beryllium
• produced using near net-shape casting
• smaller, thinner designs with greater protection of internal components
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Cell Phone Cases II
• sleek metallic surface
• scratch and corrosion resistant
• ~2.5 times strength of titanium alloy
• ~1.5 times hardness of stainless steel
• non-reactive
• thinner walls with greater strength
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Cell Phone Hinges
• deformation resistant high yield strength and elasticity
• more durable than conventional materials
• very resilient to impact and daily wear-and-tear
• reliable in repeated load-bearing conditions
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References
• http://www.liquidmetal.com/• http://www.jhu.edu/news/home06/jan06/glass.html• http://engr.oregonstate.edu/momentum/stories/liquid_metal.html• http://www.jhu.edu/matsci/people/faculty/hufnagel/
background.html• http://www.nature.com/nature/journal/v439/n7075/full/
439405a.html;jsessionid=396A417548AD57212FA5DAF138B540CA
• http://www.sciencedaily.com/releases/1998/03/980331074950.htm
• B. Van Aken, P. de Hey, and J. Sietsma: Structural relaxation and plastic flow in amorphous La50Al25Ni25. Mater. Sci. Eng. A 278, 247 (2000).
• http://www.sciwrite.caltech.edu/journal03/owensmichael.html