What Is Nitinol?

Nitinol is a superalloy composed of Nickel and Titanium, it has a few extremely interesting and useful properties that set it apart from other alloys, including shape memory and hyperelasticity. Don’t worry if those two things are unfamiliar to you, we’ll explain them in detail in this blog.

What actually is Nitinol?

The name Nitinol is derived from both its composition and where it was discovered: Nickel, Titanium, Naval Ordnance Laboratory. The NOL was a US military center for research and development, which in 1959 accidentally invented Nitinol.

Originally formulated solely to be a corrosion-resistant alloy, Nitinol was discovered to have some extraordinary properties that soon overshadowed, but in most applications complemented, its impressive corrosion resistance.

Why is it so Expensive?

Although invented in 1959 it took many years for Nitinol to be commercially available. Part of the reason for this is the high level of control needed to create the alloy. Vacuum Arc Remelting is utilized to combine Titanium and Nickel, a process with high operating costs.

Furthermore, as with many alloys, the composition is critical to the functionality of nitinol, a change of just 1% in the ratio of Ni to Ti can affect the transition temperature – and thus the usability of the product – by up to 100 degrees Celsius.

These factors combined with the relatively high cost of the raw materials needed; namely Titanium, explain why Nitinol is so expensive per unit weight.

The Superelasticity of Nitinol

Nitinol can be bent and formed into complex shapes way beyond the plastic deformation point of most metals, acting almost like a flexible wire. This has enabled its use in a variety of applications.

Nitinol can be up to 30x times farther than ordinary metals, and still return to its original shape.

Shape Memory of Nitinol

Perhaps even more extraordinary is the ability for Nitinol to remember its shape. If a piece of Nitinol wire is formed into a shape at a certain temperature, often around 500 degrees C, it will return to that shape when reheated to its transition temperature, which is often as low as 40 degrees.

It does this due to the atomic bond between the rows of atoms trying to revert to it’s shape when hot. The change from hot to room temperature happens as the material passes from an Austenitic phase to a martensitic one.

What is the use of Nitinol?

A material like no other, nitinol has some creative and unique uses. Whilst its corrosion resistance and high strength make it a great material for medical applications, the really amazing application utilizes its memory function.

Nitinol in medicine: Stents and braces

A stent is a device that holds open a vein or artery, this is often needed when a patient is suffering from a condition such as Peripheral Arterial Disease. A nitinol stent resembles a cylinder, with the wire being formed into a lattice, similar to the reinforcing seen on a garden hose.

The surgeon selects a stent with its outer diameter -in its natural state- slightly larger than the diameter of the artery affected. The stent is compressed to around half of its final diameter, allowing it to be passed easily into the artery or vein.

Once in place, the warmth of the human body causes the nitinol to remember its original shape, applying outward pressure on the wall of the vein, preventing it from collapsing.

Braces are used in dentistry to adjust the position of teeth over a period of months or years. As these devices need to be strong, corrosive resistance and extremely malleable, Nitinol is used to form the basic structure of many braces and retainers.

Practical uses for Nitinol’s memory affect

There are quite a few devices and trinkets that make use of the memory effect of Nitinol, such as acting as a motor in warm water or as novelty toys. But there are a few applications of this phenomenon that are extremely useful.

Because almost all metals heat up when an electric current is passed through them, a piece of Nitinol can be used as an actuator, exerting a force on a system, simply through an electrical circuit being made. This is perfect for situations where electrical motors, or hydraulic systems would be too bulky and impractical.