The Future is now—Shape Memory Alloys

Introduction to Shape Memory Alloys

Although it sounds like science fiction, metals that can shape-shift and “remember” their previous forms are used today throughout the automotive, aerospace, biomedical and robotic industries.

Since their uses are so diverse, these metals go by many names, including shape memory alloy (SMA), smart metal, muscle wire and smart alloy. Simply speaking, SMAs are specially formulated mixtures of metal that can re-work themselves back into their original shapes after being deformed. The trick here is to heat up the deformed SMA to its “transition temperature”, which activates the SMAs memory property so that it returns to its prior shape. Of course, the alloy does not actually remember its original shape as a person remembers what they ate for breakfast. Instead, when the SMA is manufactured, the metals are processed in such a way that establishes a "parent shape."

In their 1993 paper “Memory Metal,” George Kauffman and Issac Mayo describe the process for manufacturing one of the most versatile and common SMAs, a combination of nickel and titanium called nitinol. “The metal must be held in position and heated to about 500 ° C. The high temperature causes the atoms to arrange themselves into the most compact and regular pattern possible, resulting in a rigid cubic arrangement known as the austenite phase.” After this phase is established—a process also called training—it is ready to be used.

[1]

SMAs can be broken down into two types; either they have one-way memory or a two-way memory. One-way memory indicates that the metal can be shaped and reshaped to hold different positions, but once exposed to its transition temperature, it returns to its parent shape. The two-way memory effect is seen in SMAs that train the metal to remember one shape at a lower temperature and a different shape at a high temperature.

The way they are used varies by industry; SMAs have been included in aerospace designs for quieter engines, shape-memory coupling for oil line and water pipes, the seats of cars, the “muscles” of robots and more. Medical applications of SMAs have been very successful. SMA stents are used in peripheral artery angioplasty procedures to keep arteries open, SMA allows for flexible eyeglass frames and dental braces that exert a constant force on the wearer’s teeth.

If you haven’t seen shape memory alloys in action yet, you probably will. New uses for them are being envisioned every day. From smart phones to robotics to engines, SMAs are a futuristic material that is being used right now.

[1]

Examples of Shape Memory Alloys

There are several types of Shape Memory Alloys, but the most commonly used are those based on the following metals:

1. Nickel-Titanium (NiTi): Often referred to as "Nitinol," this is the most widely known and used SMA. It is an alloy made of nickel and titanium and is particularly well-known for its excellent shape memory properties and biocompatibility, making it ideal for medical applications such as stents, guidewires, and dental braces.

2. Copper-Based Alloys: Copper-aluminum-nickel and copper-zinc-aluminum alloys are other types of SMAs. While not as widely used as Nitinol, they still find application in areas like actuators, robotics, and automotive components. Copper-based alloys are typically less expensive but also exhibit different mechanical properties compared to nickel-titanium alloys.

3. Iron-Based Alloys: These are relatively newer in comparison to the other types of SMAs and are used for specific applications in aerospace and other industries where higher strength is required. They are often developed for specialized engineering projects.

Uses of Shape Memory Alloys

Shape Memory Alloys have found applications across many industries due to their unique properties, ranging from medical devices to aerospace technologies. Some of the key uses of SMAs include:

1. Medical Applications: SMAs are widely used in the medical field, particularly in devices that require minimal invasiveness or need to function under certain conditions. A well-known example is the use of Nitinol in stents, which are small mesh tubes inserted into blocked blood vessels. Once inserted, the stent is expanded by body temperature, returning to its original shape to open the vessel. SMAs are also used in guidewires for minimally invasive surgeries, orthodontic devices such as braces, and surgical staples.

2. Actuators: Shape Memory Alloys are used in actuators that convert thermal energy into mechanical work. In various industrial applications, SMAs can be used in pumps, valves, and other devices that require a controlled motion. The alloys provide a simple and reliable mechanism for movement, driven by temperature changes, and they are often used in automatic or self-regulating systems.

3. Aerospace and Robotics: SMAs are used in aerospace applications for actuators and for controlling aerodynamic surfaces, such as the flaps and rudders of aircraft, where they can respond to temperature changes in flight. In robotics, SMAs can be used to mimic the movement of muscles, making them valuable for soft robotics, which require flexible and adaptive materials.

4. Consumer Electronics: SMAs are increasingly being used in consumer electronics, particularly in devices that require compact size and flexibility. Examples include cameras with self-adjusting lenses, automatic eyeglasses, and some actuating mechanisms in wearable technology.

5. Automotive Industry: In the automotive industry, SMAs are used for smart systems such as temperature-controlled seats, automatic mirrors, and as part of the actuation systems in vehicles. These alloys help create more efficient and compact mechanisms compared to traditional materials.

6. Smart Materials and Systems: SMAs can also be incorporated into smart materials and systems, which are used for applications that require responsiveness to environmental stimuli. These could be used in buildings or infrastructure where materials change shape in response to temperature fluctuations, providing self-healing or adaptive features.

Conclusion

Shape Memory Alloys represent a significant breakthrough in material science thanks to their ability to return to a predefined shape under the influence of temperature. From medical stents and actuators to aerospace applications, SMAs have proven to be invaluable materials with vast potential for future innovations. As research into SMAs continues, it’s likely that we will see even more advanced uses of these materials in the coming years, further enhancing their value in both industrial and everyday applications. For more details, please check Stanford Advanced Materials (SAM).  

Reference:

[1] NASA (2025, February 20). NASA’s Shape Memory Materials Open Doors for Smart Tech. NASA TECHNOLOGY TRANSFER PROGRAM. Retrieved February 20, 2025, from https://technology.nasa.gov/