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 boundaries, the weak spots of crystalline materials, leads to better resistance to wear and corrosion. Amorphous metals, while technically glasses, are also much tougher and less brittle than oxide glasses and ceramics. Amorphous metals can be grouped in two categories, as either non-ferromagnetic, if they are composed of Ln, Mg, Zr, Ti, Pd, Ca, Cu, Pt and Au, or ferromagnetic alloys, if they are composed of Fe, Co, and Ni.
Thermal conductivity of amorphous materials is lower than that of crystalline metal. 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 prolonging the time the molten metal stays in supercooled state.
As temperatures change, the electrical resistivity of amorphous metals behaves very different than that of regular metals. While the resistivity in regular metals generally increases with temperature, following the Matthiessens rule, the resistivity in a large number of amorphous metals is found to decrease with increasing temperature. This is effect can be observed in amorphous metals of high resistivities between 150 and 300 microohm-centimeters. In these metals, the scattering events causing the resistivity of the metal can no longer be considered statistically independent, thus explaining the breakdown of the Matthiessens rule. The fact that the thermal change of the resistivity in amorphous metals can be negative over a large range of temperatures and correlated to their absolute resistivity values was first observed by Mooij in 1973, hence coining the term "Mooij-rule".
The alloys of boron, silicon, phosphorus, and other glass formers with magnetic metals (iron, cobalt, nickel) have high magnetic susceptibility, with low coercivity and high electrical resistance. Usually the electrical conductivity of a metallic glass is of the same low order of magnitude as of a molten metal just above the melting point. The high resistance leads to low losses by eddy currents when subjected to alternating magnetic fields, a property useful for e.g. transformer magnetic cores. Their low coercivity also contributes to low loss.
The superconductivity of amorphous metal thin films was discovered experimentally in the early 1950s by Buckel and Hilsch.
For certain metallic elements the superconducting critical temperature T can be higher in the amorphous state (e.g. upon alloying) than in the crystalline state, and in several cases T increases upon increasing the structural disorder. This behavior can be understood and rationalized by considering the effect of structural disorder on the electron-phonon coupling.
Amorphous metals have higher tensile yield strengths and higher elastic strain limits than polycrystalline metal alloys, but their ductilities and fatigue strengths are lower. 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, 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 composites 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.