Thursday, May 17, 2012

Metals that can be molded like plastics


The original article is very good at describing the situation and solution to making metals that are less like hard, orderly crystals and more like grainy, moldable, "amorphous" materials like glass and plastic. The method involves cooling the metal quickly enough so that its molecules don't have enough time to settle down in an orderly configuration and must "freeze" where they are. However, this is practically impossible with pure metals since they have all the same atoms and are extremely orderly to begin with. You can't remove heat fast enough. So alloys are made where the mixture of atoms has a distribution of sizes that do not settle easily.

The first alloy was created in the lab in 1960, from three atoms of silver for each atom of silicon. However, "elaborate means were required to cool the samples fast enough, and they had to be small and thin—wires, ribbons, or foils less than 100 micrometers thick."

In the 1990s, researchers at CalTech made a better alloy with a lower "critical cooling rate."

The first commercial amorphous metal alloy was brought to market in 2003 by CalTech spin-off Liquidmetal Technologies. Called Vitreloy 1, it’s about 40% zirconium, 20% berylium, and 10% each of titanium, copper, and nickel.
Vitreloy 1 and its successors have a number of exceptional properties. They are strong, hard, and (unlike crystalline metals) they do not shrink appreciably on freezing, and thus can be injection-molded, blow-molded, and otherwise formed using the same economical processes as plastics. Designing tooling for amorphous metals requires paying attention to the critical cooling rate of the material; if some volume of the part cools too slowly, the alloy there will crystallize, shrink, and spoil it.
Again, read the original article, it has the best information there.

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