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An amorphous metal (also known 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 alloying.〔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.〕 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) had been produced; these are known as bulk metallic glasses (BMG). Liquidmetal sells a number of titanium-based BMGs, developed in studies originally performed at Caltech. More recently, batches of amorphous steel have been produced that demonstrate strengths much greater than conventional steel alloys. ==History== The first reported metallic glass was an alloy (Au75Si25) produced at Caltech by W. Klement (Jr.), Willens and Duwez in 1960. 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 77.5% palladium, 6% copper, and 16.5% silicon was found to have critical cooling rate between 100 to 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 wheel. 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 and a room temperature saturation magnetization of 1.56 teslas. In the early 1980s, glassy ingots with 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, the achievable thickness was increased to a centimeter. 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. Al-based metallic glasses containing Scandium exhibited a record-type tensile mechanical strength of about 1500 MPa. 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 (41.2% Zr, 13.8% Ti, 12.5% Cu, 10% Ni, and 22.5% Be), was developed at Caltech, as a part of Department of Energy and NASA research of new aerospace materials. More variants followed. In 2004, two groups succeeded in producing bulk amorphous steel (actually rather cast iron owing to high C content), one at Oak Ridge National Laboratory, the other at University of Virginia. The Oak Ridge group refers to their product as "glassy steel," while the University of Virginia group referred to theirs as "DARVA-Glass 101".〔U.Va. News Service, ("University Of Virginia Scientists Discover Amorphous Steel Material is three times stronger than conventional steel and non-magnetic" ), ''U.Va. News Services'', 7/2/2004〕〔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〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Amorphous metal」の詳細全文を読む スポンサード リンク
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