Metallic Glasses in Cell Phones

Angelika Franz

Outline

• what is a metallic glass

• structure

• properties

• processing

• cell phone cases

• cell phone hinges

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)

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

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

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

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

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

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

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

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

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

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

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