Researchers Create New 'Memory' Metals That Could Improve Safety

Some metal alloys will "remember" a shape when you heat them to the same temperature they were originally shaped at. So a straight wire made from one of these "shape memory alloys" might change back into a spring when heated, or vice versa. But the alloys that exist today change shape at low temperatures. Materials scientists at Sandia National Laboratory have developed new alloys that don't change shape until they reach hundreds of degrees, opening the door to thousands of new applications.

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If you've every straightened out a wire coat hanger, you know that once it's unbent, it doesn't bend back up on its own. But certain mixtures of metals remember their original shape and will re-bend themselves under the right conditions. Scientists at a Department of Energy National Laboratory have developed a new class of these materials with some remarkable properties.

NPR's Joe Palca is always looking around for interesting inventions, as part of a project we're calling Joe's Big Idea, he found this one in New Mexico.

JOE PALCA, BYLINE: The metal mixtures that have this memory property are called shape memory alloys. Here's how they work. Let's say you have a wire made out of one these alloys to set its memory you heat the wire up and give it to the shape you want. Let's say you just want a simple, straight wire. When it cools down you twist the wire, coil it, fold it - whatever. And then...

DON SUSAN: When it heats back up, it remembers the high temperature shape that you set in it originally.

PALCA: Don Susan is a material scientist at the Sandia National Laboratory in Albuquerque. He's set up a little demo for me at this lab bench. There's some wires and a glass beaker with boiling water.

SUSAN: Here's a shape memory allow wire that the remembered shape is straight. And we can make it into whatever we want.

PALCA: Don Susan starts bending the wire.

SUSAN: Coil it up.

PALCA: Then he holds the coiled up wire over boiling water...

SUSAN: It happens pretty fast.

PALCA: ..and dips the wire in. I don't know if you can hear that, but that clink is the wire smacking against the side of the beaker as it returns to its straight shape. Don Susan says the shape change occurs with considerable force, force you can use to flip a switch or pull a pin.

These shape memory alloys are used today in medical devices, plumbing fixtures, even household appliances. The materials they're developing in New Mexico are different.

SUSAN: The new alloys that we're working on, they transform at higher temperatures.

PALCA: Commercially available memory alloys are made of nickel and titanium. They transform shape at room temperatures or body temperature, by adding one of three other metals...

SUSAN: Platinum, palladium or hafnium.

PALCA: ...Don Susan and his colleagues are raising the shape changing temperature considerably - hundreds of degrees. And what does he plan to do with these high temperature shape memory alloys?

SUSAN: We like the idea of using these alloys in safety devices, fail-safe devices.

PALCA: Here's how that would work. Let's say you want to make sure that a bomb on a fighter jet won't go off accidentally. You could make a shape that would let the bomb function under normal circumstances. But if the plane caught fire, the shape would change all on its own - maybe pulling out a pin or breaking an electrical connection.

SUSAN: Because these alloys will do their function in the fire perform and saving function. And so we like that.

PALCA: What's not to like?

Don Susan says fail-safe weapons are just the start. He sees thousand of potential uses for these high temperature shape memory alloys.

Joe Palca, NPR News.

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