Nitinol: How Smart is this Metal?

Smart materials respond to things that happen around them. One such smart material is Nitinol. Nitinol is a mixture of two different metals: nickel and titanium. Nitinol stands for Ni (nickel), Ti (titanium), and Naval Ordinance Laboratory, the place where it was discovered in 1959. The question is, what makes Nitinol so smart?

Everything around us is made of tiny building blocks called atoms. The same type of atoms belong to the same element, and different atoms are of different elements. Nitinol is made up of two kinds of atoms: Nickel atoms and Titanium atoms. They are arranged in an organized pattern called a crystal structure. Most solids have a crystal structure, and they possess this crystal structure as long as the material is solid.

However, Nitinol is special because it has two different crystal structures, also called solid phases. At colder temperatures, Nitinol’s atoms are in one arrangement, called martensite. At higher temperatures, Nitinol’s atoms are in a slightly different crystal structure, called austenite. When you heat Nitinol, you give the atoms energy to move from the martensite structure to the austenite structure, and as it cools back down, the atoms move back.

When this happens, the atoms in Nitinol move just a little bit, but this makes a huge difference in how the metal feels and behaves. At lower temperatures, Nitinol is soft and easy to bend. At hotter temperatures, it is stiff and springy. How does that make Nitinol a smart material? When it is in its low-temperature structure, it feels like rubber and can be bent easily. When heated up, it becomes stiff and goes back to its original shape, which it had before being bent. This gives Nitinol its other name, memory metal. Its unique property of going back to its original shape when it is heated to a certain temperature has numerous applications in a variety of fields.

Like many other great discoveries, Nitinol was made accidentally. Scientists were attempting to make an alloy resistant to heat and corrosion, and when a sample of Nitinol was analysed in a meeting, they realised how what they had made was perhaps even more important. They immediately recognised the potential Nitinol had, but it took more than 20 years to commercialize the metal. This was mainly due to the financial difficulties that companies encountered while melting and processing the alloy.

While Nitinol did not immediately take off, it revolutionized quite a few industries when it did. It is now extensively used in robotics as well as medical equipment. It is superelastic (ten times more flexible than other metals) which make its properties unique and sought-after.

Nitinol’s shape memory means it is most commonly used in tight spaces, where conventional machinery or mechanisms cannot be utilised. It is used in dentistry to make wires and brackets that connect teeth, to make tubing, and wires for locating and marking breast tumours as well. It is fair to say that Nitinol has made a lot of processes and techniques easier; all credit must go to the accidental discovery made in 1959 when those involved were trying to make something entirely different, though that would arguably not have had as much of an impact as the so-called ‘memory metal’.

This article is by a guest writer. While all articles are read by TBP before being published, we do not necessarily endorse the writer's opinions in any way.

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