When metal alloys are melted, the atoms lose their ordered structure and become amphorous, as seen above. Most metals alloys will snap back to their rigid crystal structures when cooled back down but bulk metallic alloys will retain the random amorphous structure even in the solid state. (Image courtesy of the Vlassak Group/Harvard SEAS.)
Enter bulk metallic glasses, also known as amorphous metals – alloys that lack the crystalline structure of most metallic solids. Like other glasses, metallic glasses soften and flow upon heating, making them well-suited to injection molding applications.
Until recently, however, bulk metallic glasses have been difficult to identify and expensive to create. These alloys are created from three or more different metals, and the only way to identify an amorphous alloy was to mix the alloy, cool it under the right conditions and then physically determine whether its structure is crystalline. In addition to this, most known metallic glasses include expensive elements, such as gold and palladium.
Fortunately, researchers at Harvard, Duke, and Yale can now predict which combinations of metals will form amorphous alloys prior to actually synthesizing them. This is thanks to careful examination of the combinations of metals’ crystalline properties.
When cooled, most alloys will crystallize, forming a single crystal structure throughout the material. Others, however, have a variety of crystal patterns which could potentially be formed. In amorphous metals, these potential patterns have similar formation energies, and compete to form simultaneously within the alloy.
Predicting the Formation of Bulk Metallic Glass
The research team identified the “critical size” that a crystalline area must reach in order to produce crystalline growth throughout the metal and predicted that simultaneous formations of many crystalline nuclei can prevent any one nucleus from reaching this critical size. This prevents the formation of any one crystal structure, and forces the alloy to remain amorphous in its solid state.
The team created and analyzed a database of potential crystal structures of alloys, then tested the predictions resulting from the analysis. The experiments found that the analysis was 73 percent accurate.
The research team has published their findings in the journal Nature Communications.
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