Tue . 18 Sep 2018

Amorphous metal

amorphous metal, amorphous metal transformer
An amorphous metal also known as metallic glass or glassy metal is a solid metallic material, usually an alloy, with a disordered atomic-scale structure Most metals are crystalline in their solid state, which means they have a highly ordered arrangement of atoms Amorphous metals are non-crystalline, and have a glass-like structure But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity There are several ways in which amorphous metals can be produced, including extremely rapid cooling, physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying12

In the past, small batches of amorphous metals have been produced through a variety of quick-cooling methods For instance, amorphous metal ribbons have been produced by sputtering molten metal onto a spinning metal disk melt spinning The rapid cooling, on the order of millions of degrees a second, is too fast for crystals to form and the material is "locked" in a glassy state More recently a number of alloys with critical cooling rates low enough to allow formation of amorphous structure in thick layers over 1 millimeter have been produced; these are known as bulk metallic glasses BMG More recently, batches of amorphous steel with three times the strength of conventional steel alloys have been produced

Contents

  • 1 History
  • 2 Properties
  • 3 Applications
  • 4 Modeling and theory
  • 5 See also
  • 6 References
  • 7 External links

Historyedit

The first reported metallic glass was an alloy Au75Si25 produced at Caltech by W Klement Jr, Willens and Duwez in 19603 This and other early glass-forming alloys had to be cooled extremely rapidly on the order of one megakelvin per second, 106 K/s to avoid crystallization An important consequence of this was that metallic glasses could only be produced in a limited number of forms typically ribbons, foils, or wires in which one dimension was small so that heat could be extracted quickly enough to achieve the necessary cooling rate As a result, metallic glass specimens with a few exceptions were limited to thicknesses of less than one hundred micrometers

In 1969, an alloy of 775% palladium, 6% copper, and 165% silicon was found to have critical cooling rate between 100 and 1000 K/s

In 1976, H Liebermann and C Graham developed a new method of manufacturing thin ribbons of amorphous metal on a supercooled fast-spinning wheel4 This was an alloy of iron, nickel, phosphorus and boron The material, known as Metglas, was commercialized in the early 1980s and is used for low-loss power distribution transformers Amorphous metal transformer Metglas-2605 is composed of 80% iron and 20% boron, has Curie temperature of 373 °C and a room temperature saturation magnetization of 156 teslas5

In the early 1980s, glassy ingots with 5 mm diameter were produced from the alloy of 55% palladium, 225% lead, and 225% antimony, by surface etching followed with heating-cooling cycles Using boron oxide flux, the achievable thickness was increased to a centimeterclarification needed

Research in Tohoku University6 and Caltech yielded multicomponent alloys based on lanthanum, magnesium, zirconium, palladium, iron, copper, and titanium, with critical cooling rate between 1 K/s to 100 K/s, comparable to oxide glassesclarification needed

In 1988, alloys of lanthanum, aluminium, and copper ore were found to be highly glass-forming Al-based metallic glasses containing Scandium exhibited a record-type tensile mechanical strength of about 1500 MPa7

In the 1990s new alloys were developed that form glasses at cooling rates as low as one kelvin per second These cooling rates can be achieved by simple casting into metallic molds These "bulk" amorphous alloys can be cast into parts of up to several centimeters in thickness the maximum thickness depending on the alloy while retaining an amorphous structure The best glass-forming alloys are based on zirconium and palladium, but alloys based on iron, titanium, copper, magnesium, and other metals are also known Many amorphous alloys are formed by exploiting a phenomenon called the "confusion" effect Such alloys contain so many different elements often four or more that upon cooling at sufficiently fast rates, the constituent atoms simply cannot coordinate themselves into the equilibrium crystalline state before their mobility is stopped In this way, the random disordered state of the atoms is "locked in"

In 1992, the commercial amorphous alloy, Vitreloy 1 412% Zr, 138% Ti, 125% Cu, 10% Ni, and 225% Be, was developed at Caltech, as a part of Department of Energy and NASA research of new aerospace materials More variants followedcitation needed

In 2004, bulk amorphous steel actually rather cast iron owing to high C content was successfully produced by two groups: one at Oak Ridge National Laboratory, who refers to their product as "glassy steel", and the other at the University of Virginia, calling theirs "DARVA-Glass 101"89 The product is non-magnetic at room temperature and significantly stronger than conventional steel, though a long research and development process remains before the introduction of the material into public or military use1011

Propertiesedit

Amorphous metal is usually an alloy rather than a pure metal The alloys contain atoms of significantly different sizes, leading to low free volume and therefore up to orders of magnitude higher viscosity than other metals and alloys in molten state The viscosity prevents the atoms moving enough to form an ordered lattice The material structure also results in low shrinkage during cooling, and resistance to plastic deformation The absence of grain boundaries, the weak spots of crystalline materials, leads to better resistance to wearcitation needed and corrosion Amorphous metals, while technically glasses, are also much tougher and less brittle than oxide glasses and ceramics

Thermal conductivity of amorphous materials is lower than that of crystalline metal As formation of amorphous structure relies on fast cooling, this limits the maximum achievable thickness of amorphous structures

To achieve formation of amorphous structure even during slower cooling, the alloy has to be made of three or more components, leading to complex crystal units with higher potential energy and lower chance of formation The atomic radius of the components has to be significantly different over 12%, to achieve high packing density and low free volume The combination of components should have negative heat of mixing, inhibiting crystal nucleation and prolonging the time the molten metal stays in supercooled state

The alloys of boron, silicon, phosphorus, and other glass formers with magnetic metals iron, cobalt, nickel have high magnetic susceptibility, with low coercivity and high electrical resistance Usually the conductivity of a metallic glass is of the same low order of magnitude as of a molten metal just above the melting point The high resistance leads to low losses by eddy currents when subjected to alternating magnetic fields, a property useful for eg transformer magnetic cores Their low coercivity also contributes to low loss

Amorphous metals have higher tensile yield strengths and higher elastic strain limits than polycrystalline metal alloys, but their ductilities and fatigue strengths are lower12 Amorphous alloys have a variety of potentially useful properties In particular, they tend to be stronger than crystalline alloys of similar chemical composition, and they can sustain larger reversible "elastic" deformations than crystalline alloys Amorphous metals derive their strength directly from their non-crystalline structure, which does not have any of the defects such as dislocations that limit the strength of crystalline alloys One modern amorphous metal, known as Vitreloy, has a tensile strength that is almost twice that of high-grade titanium However, metallic glasses at room temperature are not ductile and tend to fail suddenly when loaded in tension, which limits the material applicability in reliability-critical applications, as the impending failure is not evident Therefore, there is considerable interest in producing metal matrix composites consisting of a metallic glass matrix containing dendritic particles or fibers of a ductile crystalline metal

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 equipmentcitation needed

Thin films of amorphous metals can be deposited via high velocity oxygen fuel technique as protective coatings

Applicationsedit

Currently the most important application is due to the special magnetic properties of some ferromagnetic metallic glasses The low magnetization loss is used in high efficiency transformers amorphous metal transformer at line frequency and some higher frequency transformers Amorphous steel is a very brittle material which makes it difficult to punch into motor laminations13 Also electronic article surveillance such as theft control passive ID tags, often uses metallic glasses because of these magnetic properties

Amorphous metals exhibit unique softening behavior above their glass transition and this softening has been increasingly explored for thermoplastic forming of metallic glasses14 Such low softening temperature allows for developing simple methods for making composites of nanoparticles eg carbon nanotubes and BMGs It has been shown that metallic glasses can be patterned on extremely small length scales ranging from 10 nm to several millimeters15 This may solve the problems of nanoimprint lithography where expensive nano-molds made of silicon break easily Nano-molds made from metallic glasses are easy to fabricate and more durable than silicon molds The superior electronic, thermal and mechanical properties of BMGs compared to polymers make them a good option for developing nanocomposites for electronic application such as field electron emission devices16

Ti40Cu36Pd14Zr10 is believed to be noncarcinogenic, is about three times stronger than titanium, and its elastic modulus nearly matches bones It has a high wear resistance and does not produce abrasion powder The alloy does not undergo shrinkage on solidification A surface structure can be generated that is biologically attachable by surface modification using laser pulses, allowing better joining with bone17

Mg60Zn35Ca5, rapidly cooled to achieve amorphous structure, is being investigated, at Lehigh University, as a biomaterial for implantation into bones as screws, pins, or plates, to fix fractures Unlike traditional steel or titanium, this material dissolves in organisms at a rate of roughly 1 millimeter per month and is replaced with bone tissue This speed can be adjusted by varying the content of zinc18

Modeling and theoryedit

Bulk metallic glasses BMGs have now been modeled using atomic scale simulations within the density functional theory framework in a similar manner to high entropy alloys1920 This has allowed predictions to be made about their behavior, stability and many more properties As such, new BMG systems can be tested, and tailored systems; fit for a specific purpose eg bone replacement or aero-engine component without as much empirical searching of the phase space and experimental trial and error

See alsoedit

  • Bioabsorbable metallic glass
  • Glass-ceramic-to-metal seals
  • Liquidmetal
  • Materials science
  • Structure of liquids and glasses
  • Amorphous brazing foil

Referencesedit

  1. ^ Some scientists only consider amorphous metals produced by rapid cooling from a liquid state to be glasses However, materials scientists commonly consider a glass to be any solid non-crystalline material, regardless of how it is produced
  2. ^ Ojovan, M I; Lee, W B E 2010 "Connectivity and glass transition in disordered oxide systems" Journal of Non-Crystalline Solids 356 44–49: 2534 Bibcode:2010JNCS3562534O doi:101016/jjnoncrysol201005012 
  3. ^ Klement, W; Willens, R H; Duwez, POL 1960 "Non-crystalline Structure in Solidified Gold-Silicon Alloys" Nature 187 4740: 869–870 Bibcode:1960Natur187869K doi:101038/187869b0 
  4. ^ Libermann H & Graham C 1976 "Production Of Amorphous Alloy Ribbons And Effects Of Apparatus Parameters On Ribbon Dimensions" IEEE Transactions on Magnetics 12 6: 921 Bibcode:1976ITM12921L doi:101109/TMAG19761059201 
  5. ^ Roya, R & Majumdara, AK 1981 "Thermomagnetic and transport properties of metglas 2605 SC and 2605" Journal of Magnetism and Magnetic Materials 25: 83–89 Bibcode:1981JMMM2583R doi:101016/0304-88538190150-5 
  6. ^ Inoue, A 2000 "Stabilization of metallic supercooled liquid and bulk amorphous alloys" Acta Materialia 48: 279–306 doi:101016/S1359-64549900300-6 
  7. ^ Inoue, A; Sobu, S; Louzguine, D V; Kimura, H; Sasamori, K 2011 "Ultrahigh strength Al-based amorphous alloys containing Sc" Journal of Materials Research 19 5: 1539 Bibcode:2004JMatR191539I doi:101557/JMR20040206 
  8. ^ UVa News Service, "University Of Virginia Scientists Discover Amorphous Steel Material is three times stronger than conventional steel and non-magnetic", UVa News Services, 7/2/2004
  9. ^ Google Patents listing for Patent WO 2006091875 A2, "Patent WO 2006091875 A2 - Amorphous steel composites with enhanced strengths, elastic properties and ductilities Also published as US20090025834, WO2006091875A3", Joseph S Poon, Gary J Shiflet, Univ Virginia, 8/31/2006
  10. ^ "Glassy Steel" ORNL Review 38 1 2005 
  11. ^ Ponnambalam, V; Poon, S J; Shiflet, G J 2011 "Fe-based bulk metallic glasses with diameter thickness larger than one centimeter" Journal of Materials Research 19 5: 1320 Bibcode:2004JMatR191320P doi:101557/JMR20040176 
  12. ^ Russell, Alan & Lee, Kok Loong 2005 Structure-Property Relations in Nonferrous Metals John Wiley & Sons p 92 ISBN 9780471708537 
  13. ^ Ning, S R; Gao, J; Wang, Y G 2010 "Review on Applications of Low Loss Amorphous Metals in Motors" Advanced Materials Research 129-131: 1366 doi:104028/wwwscientificnet/AMR129-1311366 
  14. ^ Saotome, Y; Iwazaki, H 2000 "Superplastic extrusion of microgear shaft of 10 μm in module" Microsystem Technologies 6 4: 126 doi:101007/s005420050180 
  15. ^ Kumar, G; Tang, H X; Schroers, J 2009 "Nanomoulding with amorphous metals" Nature 457 7231: 868–872 Bibcode:2009Natur457868K doi:101038/nature07718 PMID 19212407 
  16. ^ Hojati-Talemi, Pejman 2011 "High performance bulk metallic glass/carbon nanotube composite cathodes for electron field emission" Applied Physics Letters 99 19: 194104 Bibcode:2011ApPhL99s4104H doi:101063/13659898 
  17. ^ Maruyama, Masaaki June 11, 2009 "Japanese Universities Develop Ti-based Metallic Glass for Artificial Finger Joint" Tech-on 
  18. ^ "Fixing bones with dissolvable glass" Institute of Physics October 1, 2009 
  19. ^ King, DM; Middleburgh, SC; Liu, ACY; Tahini, HA; Lumpkin, GR; Cortie, M January 2014 "Formation and structure of V–Zr amorphous alloy thin films" Acta Materialia 83: 269–275 doi:101016/jactamat201410016 
  20. ^ Middleburgh, SC; Burr, PA; King, DM; Edwards, L; Lumpkin, GR; Grimes, RW November 2015 "Structural stability and fission product behaviour in U3Si" Journal of Nuclear Materials 466: 739–744 Bibcode:2015JNuM466739M doi:101016/jjnucmat201504052 

External linksedit

  • Liquidmetal Design Guide
  • "Metallic glass: a drop of the hard stuff" at New Scientist
  • Glass-Like Metal Performs Better Under Stress Physical Review Focus, June 9, 2005
  • "Overview of metallic glasses"
  • New Computational Method Developed By Carnegie Mellon University Physicist Could Speed Design and Testing of Metallic Glass 2004 the alloy database developed by Marek Mihalkovic, Michael Widom, and others
  • Materials Today: The case for bulk metallic glass
  • New tungsten-tantalum-copper amorphous alloy developed at the Korea Advanced Institute of Science and Technology 1
  • Amorphous Metals in Electric-Power Distribution Applications
  • Amorphous and Nanocrystalline Soft Magnets
  • glass transition temperatures of bulk metallic glasses

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