New shape-shifting metals discovered
Date published: 07th October 2013
Currently, martensite metals are made of an alloyed mixture of nickel and titanium.
They have the remarkable ability to "remember" their shape and even after being bent will return to their original form. For this, they are called "shape memory" metals.
They have been used in spectacle frames and brassiere wires, but also in surgery as frameworks for shaping healing bones, and as "stents" for holding heart arteries open.
Martensite metals change shape when heated or cooled through a
certain temperature, when the atoms that make up their structure
rearrange themselves in a sudden transformation.
Some call this a "military transformation" because the rows of atoms that make up the metal crystal click into their new shape in an orderly manner.
The transformation means that martensite can be used in smart mechanisms that respond to temperature change.
Examples include automatic windows-openers in glasshouses, a means for automatically guiding solar panels to point at the Sun on the Hubble Space Telescope, and, very recently, in the Boeing 787 Dreamliner to morph the trailing edge of the engine cowling, making it quieter when it runs hot on take-off.
The pitfall of current martensites is that after repeated shape changes, they build up stresses inside that degrade them and eventually break them apart. The new alloy, made of a mixture of zinc, gold and copper, changes back and forth almost indefinitely with little internal damage, opening up a new range of applications for these types of "active materials".
The aim is now to apply the lessons learned from the new metal to make a family of ceramic solids that can also be shape-switched back and forth.
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