Engineers have produced a new nickel, copper and titanium “memory” alloy that that springs back into shape even after it is bent more than 10 million times.
The journal Science reported that the new shape memory alloy shatters previous records for bending and is so resilient it could be useful in artificial heart valves, aircraft components or a new generation of solid-state refrigerators.
shape memory alloys (SMAs) are already used in surgical operations and other applications. A stent, for example, might be squashed into a small space and then spring into its designed shape to prop open a blood vessel.
When SMAs are bent or otherwise structurally deformed, the stress (in the form of heat or electrical current) causes the SMA to spring back to its original design.
Yet, as a technology, the alloys have never entirely fulfilled their promise and entered the world of “high-cycle fatigue” applications.
“Usually shape memory alloys – like in minimally invasive surgery – they regain their shape once, or a few times, but not multiple times,” said Prof. Manfred Wuttig who developed the new alloy at the University of Kiel along, in Germany, along with colleagues from the University of Maryland. He is one of the paper’s senior authors and told the BBC. “This is highly unusual. It’s kind of a leap forward.”
The nickel, titanium and copper atoms are arranged in such a way that they can switch between two different configurations. This “phase transition” is what allows the alloy to snap back into shape after it has been bent. It can be triggered by heat, the metal can stay in a bent position when cold, or, in a different form of the alloy, it can happen as soon as tension is released.
The researchers’ paper in Science describes how, by embedding tiny impurity particles made from titanium-copper, SMAs can withstand deformation and re-formation up to 10 million times. This could open up SMAs for use in such high-cycle applications as refrigerator compressors and aircraft parts as well as more delicate surgical uses.