Amorphous metal

An amorphous metal (also known as metallic glass or glassy metal) is a solid metallic material, usually an alloy, with 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.Previously, small batches of amorphous metals had been produced through a variety of quick-cooling method, such as amorphous metal ribbons which had been produced by sputtering molten metal onto a spinning metal disk (melt spinning). The rapid cooling (on the order of millions of degrees Celsius a second) is too fast for crystals to form and the material is 'locked' in a glassy state. Currently, 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. An amorphous metal (also known as metallic glass or glassy metal) is a solid metallic material, usually an alloy, with 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.Previously, small batches of amorphous metals had been produced through a variety of quick-cooling method, such as amorphous metal ribbons which had been produced by sputtering molten metal onto a spinning metal disk (melt spinning). The rapid cooling (on the order of millions of degrees Celsius a second) is too fast for crystals to form and the material is 'locked' in a glassy state. Currently, 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. 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 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 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 373 °C and a room temperature saturation magnetization of 1.56 teslas. In the early 1980s, glassy ingots with 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, 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 1982, a study on amorphous metal structural relaxation indicated a relationship between the specific heat and temperature of (Fe0.5Ni0.5)83P17. As the material was heated up, the properties developed a negative relationship starting at 375 K, which was due to the change in relaxed amorphous states. When the material was annealed for periods from 1 to 48 hours , the properties developed a positive relationship starting at 475 K for all annealing periods, since the annealing induced structure disappears at that temperature. In this study, amorphous alloys demonstrated glass transition and a super cooled liquid region. Between 1988 and 1992, more studies found more glass-type alloys with glass transition and a super cooled liquid region. From those studies, bulk glass alloys were made of La, Mg, and Zr, and these alloys demonstrated plasticity even when their ribbon thickness was increased from 20 μm to 50 μm. The plasticity was a stark difference to past amorphous metals that became brittle at those thicknesses. 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. Before new techniques were found in 1990, bulk amorphous alloys of several millimeters in thickness were rare, except for a few exceptions, Pd-based amorphous alloys had been formed into rods with a 2 mm diameter by quenching, and spheres with a 10 mm diameter were formed by repetition flux melting with B2O3 and quenching.