Amorphous metal 347027 225711367 2008-07-15T01:00:12Z User A1 2062655 Reverted 1 edit by [[Special:Contributions/80.168.88.50|80.168.88.50]]; If i recall metglas is a specific metallic glass alloy, kinda like Vitreloy.. ([[WP:TW|TW]]) [[Image:Bulk Metallic Glass Sample.jpg|thumb|Sample of amorphous metal in the lab]] An '''amorphous metal''' is a [[metal]]lic material with a disordered atomic-scale structure. In contrast to most metals, which are [[crystal]]line and therefore have a highly ordered arrangement of [[atom]]s, [[amorphous solid|amorphous]] alloys are non-crystalline. Materials in which such a disordered structure is produced directly from the liquid state during cooling are called "[[glass]]es", and so amorphous metals are commonly referred to as "'''metallic glasses'''" or "'''glassy metals'''". However, there are several other ways in which amorphous metals can be produced, including [[physical vapor deposition]], [[solid-state reaction]], [[ion irradiation]], [[melt spinning]], and [[mechanical alloying]]<!-- is this kind of "mechanical alloying" really the same as "pattern welding" ? -- Isn't. Pattern welding is layering of metals, mechanical alloying works on smaller scale and is more similar to sintering. -->. Amorphous metals produced by these techniques are, strictly speaking, not glasses; however, [[materials science|materials scientists]] commonly consider amorphous alloys to be a single class of materials, regardless of how they are prepared. In the past, small batches of amorphous metals have been produced through a variety of quick-cooling methods. For instance, amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. 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) had been produced, these are known as '''bulk metallic glasses''' ('''BMG'''). [[Liquidmetal]] sells a number of titanium-based BMGs, developed in studies originally carried out at [[Caltech]]. More recently, batches of amorphous steel have been produced that demonstrate strengths much greater than conventional steel alloys. == History == The first metallic glass was an [[alloy]] (Au80Si20) produced at [[Caltech]] by [[Pol Duwez]] in 1957. This and other early glass-forming alloys had to be cooled extremely rapidly (on the order of one [[mega]][[kelvin]] per second, 10<sup>6</sup>&nbsp;K·s<sup>-1</sup>) 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 [[micrometres]]. In 1969, an alloy of 77.5% [[palladium]], 6% copper, and 16.5% silicon was found to have critical cooling rate between 100 K/s to 1000 K/s. In 1976, H. Liebermann and C. Graham developed a new method of manufacturing thin ribbons of amorphous metal on a [[melt spinning|supercooled fast-spinning wheel]].<ref>Libermann H. and Graham C., Production Of Amorphous Alloy Ribbons And Effects Of Apparatus Parameters On Ribbon Dimensions, IEEE Transactions on Magnetics, Vol Mag-12, No 6, 1976</ref> This was an alloy of [[iron]], [[nickel]], [[phosphorus]] and [[boron]]. The material, known as '''[[Metglas]]''', was commercialized in early 1980s and used for low-loss power distribution transformers ([[Amorphous metal transformer]]). Metglas-2605 is composed of 80% iron and 20% boron, has [[Curie temperature]] of {{nowrap|373 °C}} and a room temperature saturation magnetization of 125.7 [[millitesla]]s. In the early 1980s, glassy ingots with {{nowrap|5 mm}} diameter were produced from the alloy of 55% palladium, 22.5% lead, and 22.5% antimony, by surface etching followed with heating-cooling cycles. Using [[boron oxide]] [[flux (metallurgy)|flux]], the achievable thickness was increased to a centimeter. The research in [[Tohoku University]] 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 glasses. In 1988, alloys of lanthanum, aluminium, and copper ore were found to be highly glass-forming. In the 1990s, however, 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 a dozen 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 first commercial amorphous alloy, [[Vitreloy]] 1 (41.2% Zr, 13.8% Ti, 12.5% Cu, 10% Ni, and 22.5% Be), was developed at Caltech, as a part of [[United States Department of Energy|Department of Energy]] and [[NASA]] research of new aerospace materials. More variants followed. In 2004, two groups succeeded in producing bulk amorphous steel, one at [[Oak Ridge National Laboratory]], the other at [[University of Virginia]]. The Oak Ridge group refers to their product as "glassy steel". 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 use.<ref>{{cite journal |title=Glassy Steel |journal=ORNL Review |year=2005 |volume=38 |issue=1 |url=http://www.ornl.gov/info/ornlreview/v38_1_05/article17.shtml}}</ref><ref>{{cite journal |author=V. Ponnambalam, S. Joseph Poon and Gary J. Shiflet |title=Fe-based bulk metallic glasses with diameter thickness larger than one centimeter |journal=Journal of Materials Research |year=2004 |volume=19 |issue=5 |url=http://lucy.mrs.org/publications/jmr/jmra/2004/may/0176.html |pages=1320 |doi=10.1557/JMR.2004.0176}}</ref> == Properties == 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 boundary|grain boundaries]], the weak spots of crystalline materials, leads to better resistance to [[wear]] and [[corrosion]]. Amorphous metals, while technically glasses, are also much [[toughness|tougher]] and less brittle than oxide glasses and ceramics. Thermal conductivity of amorphous materials is lower than of crystals. 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 prolongs 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]]) are magnetic, with low [[coercivity]] and high [[electrical resistance]]. The high resistance leads to low losses by [[eddy current]]s when subjected to alternating magnetic fields, a property useful for eg. [[transformer]] [[magnetic core]]s. 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 (mechanics)|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 composite]] materials 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 equipment. Thin films of amorphous metals can be deposited via [[high velocity oxygen fuel]] technique as protective coatings. == References == {{reflist}} == External links == * [http://www.newscientist.com/channel/mech-tech/mg18624931.000 "Metallic glass: a drop of the hard stuff"] at [[New Scientist]] * [http://focus.aps.org/story/v15/st20 ''Glass-Like Metal Performs Better Under Stress''] Physical Review Focus, [[June 9]], [[2005]] * [https://jshare.johnshopkins.edu/thufnag1/Public_html/metallicglass.html "Overview of metallic glasses"] * [http://www.cmu.edu/PR/releases04/040902_glass.html ''New Computational Method Developed By Carnegie Mellon University Physicist Could Speed Design and Testing of Metallic Glass''] (2004) (the [http://alloy.phys.cmu.edu/ alloy database] developed by Marek Mihalkovic, Michael Widom, and others) * [http://www.materialstoday.com/pdfs_7_3/telford.pdf Materialstoday.com: Bulk metallic glass] * New tungsten-tantalum-copper amorphous alloy developed at the Korea Advanced Institute of Science and Technology [http://english.chosun.com/w21data/html/news/200505/200505060005.html] * [http://www.vacuumschmelze.de/dynamic/en/home/researchampinnovation/materialsdesign/nanocrystallinesoftmagneticmaterials.php Nanocrystalline Soft Magnetic Materials] == See also == * [[Glass-ceramic-to-metal seals]] * [[materials science]] [[Category:Metallurgy]] [[Category:Alloys]] [[Category:Amorphous solids]] [[de:Metallisches Glas]] [[fr:Alliage métallique amorphe]] [[ja:アモルファス金属]] [[zh:非晶态金属]]