The Future Is Now—Shape Memory Alloys

Although the concept originates from early theoretical models, it may appear unconventional. Metals that modify their shape and recover their initial configuration are used in the automotive, aerospace, biomedical and robotics industries.

Because of their wide range of applications, these metals are known by several names, including Shape Memory Alloy (SMA), intelligent metal, muscle wire and intelligent alloy. In simple terms, SMAs are specially formulated metal mixtures that recover their original configuration following deformation. The process involves heating a deformed SMA to its transition temperature. This heating activates the memory property and restores the alloy’s base shape. The alloy does not recall its previous configuration. Instead, a base shape is defined during production.

In a 1993 article entitled "Memory Metal", George Kauffman and Issac Mayo described the procedure for manufacturing one of the most widely applied SMAs. The alloy, composed of nickel and titanium, is known as Nitinol. It is maintained in position and heated to approximately 500 °C. The high temperature causes the atoms to arrange into a compact, regular cubic pattern, known as the austenite phase.

SMAs are categorised into two types. One-way memory alloys can be deformed and repositioned; however, upon reaching the transition temperature, they revert to their initial configuration. Two-way SMAs are engineered to adopt one shape at lower temperatures and another at higher temperatures.

SMAs are used in aerospace for quieter engines, shape-memory couplings in oil and water pipelines, automotive seating and as robotic actuators. In biomedical applications, SMA stents maintain the openness of peripheral arteries during angioplasty. SMAs are also used in flexible eyeglass frames and dental braces that exert a constant force on teeth.

If you have not observed the operation of shape memory alloys, you likely will in the near future. Each day, new applications for SMAs are developed. Applications range from smartphones and robots to engines.