Developing Beyond High Temperature Shape Memory Alloys

Have you encountered a shape-memory alloy?

Experiment with this: Untwist a finger-size spring. Hold a lighter at the bottom of the untwisted section and flick a flame. Notice how like magic the spring twirls back into its twisted shape and this is because the high temperature caused the alloy to remember its original shape.

Exploring Shape-Memory Alloys

This metal alloy property is being explored by researchers at “Sandia National Laboratories”. The project researchers are toying with the idea that these special alloys (shape-memory) could improve safety of weapons components at high temperature accidents such as fire. Don Susan, a materials scientist thinks that a thermal device made from high-temperature alloy (shape-memory) may be used to close or open a switch or lock a gear to prevent it from turning. There could be unlimited things you can do with this type of alloys.

New Alloy Compositions Developed

A project that aims to create more than just high temperature alloys, but high temperature shape-memory alloys, for weapons component is what Susan and the rest of the researchers are working on. So far they have developed new alloy compositions (nickel-titanium-hafnium, nickel-titanium-platinum, and nickel-titanium-palladium) and technical advances (step prior to patent application) for these compositions have been filed. They were also able to characterize how the materials change shape, and their ductility and strength properties.

Super-Elasticity Property Of Metals

The researchers have produced prototype parts that show shape change at certain temperatures. Additionally, they were able to demonstrate a “super-elasticity” property in higher temperature shape-memory alloys. This is a rubbery-kind of property in metals. While this particular property is not the concern of the research, Susan said that it could provide future design options. The Sandia project is on its third and final year.

Shape Change At High Temperature

The researchers discovered that alloys which remember their original shape (shape-memory alloys) work like a thermal sensor in a fire sprinkler installed in buildings. A liquid that expands and breaks a glass enclosure to trigger a switch that would then activate the sprinklers is what the thermal sensor is made of. Shape-memory alloys change shape. They don’t simply expand.

Shape Memory Alloys In Medical Application

Jim McElhanon who started the project believed that this research on shape-changing alloys at high temperature will pave the way for the creation of new devices that will significantly impact nuclear weapon safety. Shape-memory alloys have been used in various applications, one of which is in medical appliances such as stents that change shape at body temperature. At below-body temperature, a tiny stent can be squeezed to make it fit an artery. When the body temperature goes up, the inserted stent opens up the artery.

Specific High Temperature

The researched-developed alloys can change shape at below room temperature and at over 500 degrees Celsius temperature (930 degrees Fahrenheit). The commercially-available alloys can change shape at temperatures outside the range required or specified by the research. In fact, the researchers relied on higher-temperature shape-memory alloys to create their own alloys. This property of the shape-memory alloys is critical as shape change shouldn’t occur when the parts are made or when it’s exposed to the sun. They should only change shape at that specific temperature range to be useful.

Future Use Of Shape-Memory Alloys

According to Susan, future Sandia research on shape-memory allows may be useful for wind and solar energy, and possibly including satellites. He said there are many interesting possibilities worth exploring for this type of new alloys.

Isn’t this an interesting development to watch out for?