Abstract

Metallic glasses do not occur naturally but are produced by various techniques, the oldest of which is by cooling molten metals so rapidly that the atoms do not get to form regular crystalline structures. The atoms are frozen in random or nonrepeating atomic patterns similar to those found in organic glasses. By metallic it is meant that the amorphous material is composed primarily, but not necessarily exclusively, of metallic elements that exhibit the properties of metals, such as electrical or magnetic behavior.

Primarily through modification of the chemistries, glasses have been produced that can truly be considered bulk, even exceeding 1 cm in all dimensions. Besides rapid solidification into thin ribbons or flakes, there exists a wide range of techniques to produce metallic glass. Methods available include chemical means, mechanical alloying, vaporization, and solid-state reactions.

Interest is maintained in these materials because of the combination of mechanical, corrosion, electric, and magnetic properties. However, it is their ferro-magnetic properties that lead to the principal application of glassy metals. The soft magnetic properties and remarkably low coercivity offer tremendous opportunities for this application.

A limitation of metallic glass is that it exists in metastable form, which means that it tends to crystallize if heated with sufficient thermal energy to allow the kinetics of crystallization, ie, both nucleation and growth, to occur.

To form an amorphous, ie, glassy metal alloy from the liquid stat means that the crystallization step must be avoided during solidification. Traditionally, production of metallic glasses requires rapid heat removal from the material which normally involves a combination of a cooling process that has a high heat-transfer coefficient at the interface of the liquid and quenching medium, and a thin cross section in at least one-dimension. Processes not dependent on rapid solidification include plastic deformation, mechanical alloying, and diffusional transformations.

Along with magnetic and mechanical behavior, high corrosion resistance is one of the most desirable properties of metallic glasses.

The magnetic properties of glassy metals provide the only commercial use in bulk quantities.