Originally Published MPMN March 2003

SPECIAL

Amorphous metal combines high strength with ease of processing

Imagine a metal alloy whose strength exceeds that of steel and titanium, but that can be processed like a plastic. Sound far-fetched? Not to the people at Liquidmetal Technologies (Tampa, FL; www.liquidmetal.com). A zirconium-based alloy marketed by the company exhibits 2.5 times the strength of some titanium alloys and twice the strength-to-weight ratio of some aluminums. In addition to these exceptional characteristics, the alloy can be cast into net-shaped forms that significantly reduce the need for secondary finishing processes.

The secret to this innovation lies in the alloy's amorphous structure that eliminates the inherently weak spots found at molecular grain boundaries. "All metals have an amorphous structure in their liquid state," says vice president of medical products Barry Canon. "But our alloy retains this characteristic in its solid state, essentially making it like a metallic glass." Other physical benefits that result from this amorphous structure include a 2% elasticity and twice as much hardness as some stainless steels.

The lack of phase transformation during solidification also holds benefits for processing. With a lower melting point than its constituent parts, the Liquidmetal alloy can be cast into net-shaped parts without voids or defects, reducing the need for costly finishing and machining operations. Because it does not crystallize, the surface finish of parts made from the alloy is smoother and more consistent than that of die castings.

Combine all of these characteristics with biocompatibility and resistance to corrosion and wear, and it is easy to see why some companies are seeing applications for the alloy in the medical field. Surgical Specialties Corp. (Reading, PA; www.surgicalspecialties. com), for instance, began producing ophthalmic scalpel blades using Liquidmetal technology in the third quarter of 2002. Another company, Depuy Orthopedics Inc. (Warsaw, IN; www.depuy.com), recently began using the alloy to produce knee-replacement devices. Other possible product applications include pacemaker casings and medical instruments.

Norbert Sparrow, Susan Wallace, and Zachary Turke

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