University Scientists Discover
Professor Richard James and his team, including graduate student Vivek Dabade and post doctorate students Yintao Song and Xian Chen, have discovered a new shape-memory alloy made of zinc, gold and copper, which seamlessly switches between two different arrangements of atoms when prompted by a change in temperature.
The newly discovered alloy is the prototype of a family of smart metals with enhanced reversibility. The shortcoming of current martensite metals is that repeated shape changes builds up stresses inside that degrade them and eventually break them apart. To alleviate these stresses, Professor James and his team used computer modeling to find candidate alloys that would better satisfy the cofactor conditions. The result is a new crystal, made up of zinc, gold and copper that can go through 16,000 shape-shifting cycles with little internal damage, making it more robust than existing materials.
"Our aim is to make the transformations reversible so they can be applied in many situations," explains Richard James, Distinguished McKnight University Professor in the Department of Aerospace Engineering and Mechanics. "The prototype could be used in applications ranging from space vehicles to electronics to energy conversion devices."
During transformation, the alloy shows unusual microstructure, not previously seen in phase transformations. As explained by physicsworld.com, shape-memory alloys are reversible phase-change materials that can exist in two crystal-lattice structures: one that is more stable above a certain transition temperature and the other favored at lower temperatures. The ability of these crystals to respond to temperature changes and click into a new shape in an orderly manner enables their use in a variety of smart mechanisms.
"The theory for the material's ultra high reversibility and unusual microstructure can readily be adapted to other alloy systems," explains James. "Our result suggests a universal strategy for developing ultra-reliable martensitic materials particularly suited to medical, microelectronic and energy applications."
Yet the potential of these materials is greater still: of particular interest in James' group is a martensitic alloy for which one of the phases is strongly magnetic. As James explains, "These materials can be used in new ways to convert heat directly to electricity, without the need for a separate electrical generator.
Fine scale image of newly discovered shape-memory metal crystal: river-like patterns form and adjust as the metal changes shape.