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 centimeters Zr-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 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

Processing I formed by quenching at rates of 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 ml html htm B. Van Aken, P. de Hey, and J. Sietsma: Structural relaxation and plastic flow in amorphous La 50 Al 25 Ni 25. Mater. Sci. Eng. A 278, 247 (2000).