What Is Bulk Metallic Glass?
December 3, 2007
Bulk metallic glass, a.k.a. amorphous metal, appears to have a very bright future. Being twice as strong as titanium, tougher and more elastic than ceramics, and having excellent wear and corrosion resistance makes them attractive for a variety of applications. It can even be cast in a mold to near net shapes.
Conventional Metals
In an ordinary metal the atoms of the metal arrange themselves into a repeating pattern of crystals or grains with different sizes and shapes upon cooling from the liquid state. Because metals typically do not solidify into single crystals, they have inherent weaknesses.
The boundaries between the grains are weak spots and under high enough stress and temperature the grains will slide past each other resulting in metal deformation. In addition, extra atoms are often present in grains causing planes of distortion called dislocations. Dislocations easily move through metal that is under stress, again causing deformation. Grain boundaries and dislocations greatly lower a metals strength compared to its theoretical maximum.
Casting of conventional metals also requires more manufacturing steps than bulk metallic glass. Conventional metals shrink significantly as they cool in the mold from liquid to solid form and often develop surface roughness. Secondary steps are usually required to get at the final product, such as grinding and polishing.
Bulk Metallic Glass
The structure of metallic glass is very different from that of conventional metals. Rather than arranging themselves into repeating patterns of grains, the atoms of metallic glasses are “frozen” in a random, disordered structure, similar to regular window glass. It even has a smooth surface like glass. So smooth, in fact, that paint does not adhere well to metallic glass. It is this amorphous structure, lacking in grain defects, that gives metallic glasses their strength, toughness, hardness, elasticity and corrosion and wear resistance.
First discovered by Pol Duwez in 1960 at Caltech, the technique to create metallic glasses required undercooling a molten metal uniformly and rapidly. Rapidly as in 1,000,000
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