Rapid Quenching of Metallic Glasses
The first metallic glass was discovered by Pol Duwez in 1960 by taking a small molten droplet of a gold-silicon alloy, and rapidly quenching it between two copper platens (affectionately known as splat quenching). The rapid rate of cooling (on the order of 10<sup>6</sup> °C/sec) prevented the atoms from being able to move into an ordered state. This technique was eventually modified into a continuous process known as melt spinning, where a large copper wheel is rapidly rotated, and a thin stream of molten metal is sprayed onto it. The high specific heat and conductivity of the copper wheel rapidly moves heat out of the metal. Ribbons tens of microns thick, inches wide, and miles long can be generated through this technique. Metglas® is the trade name of a series of melt-spun alloys sold by Hitachi Metals. Currently, they are the largest producer of metallic glass, most of which is iron-based alloys for transformer cores.
A processing schematic for Metglas® production. Image Courtesy Metglas Inc.
Deposition of Metallic Glasses
Metallic glasses can also be produced as thin films through sputtering. In this method, atoms are slowly deposited onto a cooled substrate. By keeping the sample cold, kinetics are kept slow, and crystallization can be prevented in a greater number of alloys than melt spinning or splat quenching. The downside is only very thin films can be produced. These parts will not be structural, but they can still be used for more the functional aspects of metallic glass, such as corrosion resistance.
Metallic glasses can also be prepared through electrodeposition. The most well known alloy is amorphous nickel-phosphorus, and it, too, has been used for its anti-corrosion properties.