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Thursday, June 23, 2011

Advances in metallic glass manufacture

Glass is created by cooling a material to its solid state without allowing it to crystallize, but instead while maintaining a liquid-like flow of atoms. In contrast, the atoms in metals have a neatly arranged crystalline structure. Metallic-glass alloys are non-crystalline solids that contain metallic elements such as zirconium, titanium, copper, or nickel. Such alloys are strong and light, compared to other materials. Unfortunately, they have been difficult to manufacture.
If you’ve ever watched a glass-blower, you know that the artist usually has several minutes to shape the glass before it solidifies. Not so with metallic-glasses which will begin to crystallize almost immediately. The trick then, is to melt the metallic glass (which requires temperatures above 500 degrees Celsius), achieve the desired shape, and then refreeze the glass before it has a chance to crystallize.
William Johnson and his colleagues from Caltech have devised a new strategy for processing metallic-glass. They used Joule heating (also called ohmic heating or resistive heating) to rapidly heat a rod of metallic-glass via an electric current. The entire process takes only milliseconds, ensuring uniform heating and non-crystalline cooling.
A metallic-glass rod before heating and molding (left); a molded metallic-glass part (middle); the final product with its excess material trimmed off (right).
Credit: Marios D. Demetriou.
Meanwhile, Jan Schroers team from University has found a way to blow mold metallic glasses. They’ve been able to create all sorts of complex shapes.

Jan Schroers and his team have developed novel metal alloys that can be blow molded into virtually any shape.
Credit: Image courtesy of Yale University.

In all, the metallic-glass field is looking more and more promising.