Complete Overview About Nitinol

Many people use nitinol alloys mainly because of their shape memory effect or Hyper-elastic effect. So, do you know how these two characteristics of it work? This article will take you through a comprehensive understanding of nitinol alloy and its working principle.

What is nitinol?

Nitinol is an alloy composed of nickel and titanium, where Ni represents the chemical symbol for nickel, Ti represents the chemical symbol for titanium, and NOL is the abbreviation of the name of the United States Navy Ordnance Laboratory. The density of nitinol alloy is approximately 6.45g/cm ³, its hardness is about 200HV – 400HV, its tensile strength is relatively high, approximately 500-1000MPa, and its yield strength is about 300-600Mpa.

What is nitinol composed of?

The main properties of nitinol is nickel and titanium, with the atomic ratio of the two being nearly equal, usually each accounting for 50%, namely Ni₅₀Ti₅₀ or Ni₅₅Ti₄₅,( This refers to the specific gravity of the atoms contained inside rather than the specific gravity of the weight.) In addition, some impurity elements will also be added, such as copper (Cu), niobium (Nb), vanadium (V), carbon (C), oxygen (O), etc.

How was nitinol discovered?

In the 1960s, at an experimental exhibition, William J. Buehler left a crumpled thin plate of nitinol alloy on the table. Because he heard that the knocking sound between it and the table surface was dull rather than the characteristic crisp sound of metal, he took the plate home for research. By accident, he dropped soot on the nitinol plate. The residual heat from the ash heated the nitinol plate, which made the wrinkled nitinol plate spread out. After this, William J. Buehler and Frederick Wang conducted systematic research on nitinol alloys and finally determined the shape memory effect and Hyper-elastic effect of nitinol alloys.

Two crystal phases of nitinol

• • Austenite phase

When the temperature reaches a certain level, nitinol will transform into the austenite phase. It has a body-centered cubic lattice structure, and its atoms are symmetrically and orderly arranged inside, making it very stable. During this process, You can express the temperature at which nitinol transforms into the austenite phase as AF.

• Martensitic phase

Martensite and austenitic are opposites, and when the temperature is particularly low, nitinol transforms into the martensitic phase, which has a monoclinic crystal structure with a chaotic and asymmetrical arrangement of atoms inside. There is also a higher hardness of martensitic than austenite.

Due to the influence of external temperature and pressure, martensitic and austenite will convert to each other.

And in this process, when martensitic begins to transform into austenite, this temperature is AS; When martensitic completes its transformation to austenite, this temperature is AF; When austenite begins to transition to martensitic, this temperature is MS; When austenite completes its transformation to martensitic, this temperature is MF. These four are relatively important node temperatures, usually MF<MS<AS<AF. Because when the temperature rises, the nitinol material begins to transform into austenitic and when the temperature decreases, the nitinol material begins to transform into martensitic.

How does nitinol work?

• • Shape memory alloy

Firstly, when the temperature is very high, Nitinol is in the austenite phase, and at this time, the nitinol material remains in an initial state.

However, when the temperature drops below MF, it will transform into the martensite phase, and at this time, the nitinol material remains in a new state. When reheated and the temperature rises, a new phase transformation occurs, and martensite changes back to austenite.

At this point, the nitinol material will return to its initial state. This process is the shape memory property of nitinol.

• Hyper-elastic effect

The Hyper-elastic of nitinol is usually a property at a constant temperature.

At this time, an external force is applied to the nitinol material, and it will change from austenitic to martensitic state. When the external force is canceled, the nitinol material will change back to the austenitic state, and the material will also return to its original shape.

You can find that the Hyper-elastic of nitinol is independent of temperature. This is the magic of nitinol materials, no matter what form you use to deform it with external force, as long as the external force is canceled, it will immediately return to its original state, which is important in the nitinol application.

What is nitinol used for?

Medical field: Mainly applied in medical devices, such as cardiovascular stents, orthodontic wires, orthopedic implants, surgical guide wires, catheters, endoscope components, etc. Nitinol wire is often used in these scenarios.

In the aerospace field, nitinol alloys are mainly applied in the manufacturing of connecting pipe fittings for satellite antennas, aircraft pipelines and solar panels.

Spectacle frame: Mainly made of nitinol alloy for the eye legs, it can return to its original shape when bent and is very durable.

The super-elastic steel rims in women’s underwear also use nitinol alloy, which can provide better support and fit the human body more closely.

More about nitinol application you could refer our blog: Complete Guide to Nitinol Uses and Applications

Conclusion

By having a comprehensive understanding of nitinol, you will find that its most prominent features are shape memory effect and Hyper-elastic effect. Many application scenarios precisely utilize these two characteristics. I have to sigh that nitinol is a very intelligent material, it can actually remember its initial shape, making nitinol very versatile.

FAQ

• • Is nitinol magnetic?

Nitinol has no magnetism, so it is often used in medical magnetic resonance examinations.

• Is the price of Nitinol higher than that of titanium?

The price of Nitinol is higher than that of titanium. This is because the processing technology of Nitinol is very complex, and the research and development of the alloy formula also requires a large cost. All these factors make the price of Nitinol expensive.

• What does nitinol stand for?

Nitinol is an alloy composed of nickel and titanium, where Ni represents the chemical symbol for nickel, Ti represents the chemical symbol for titanium, and NOL is the abbreviation of the name of the United States Navy Ordnance Laboratory.

• How to make nitinol

THT is a nitinol factory, we could manufacture nitinol plate, nitinol tube, nitinol rod, nitinol wire, you could contact us if you would like to get nitinol.

• How to shape nitinol?

1. Bend the nickel-titanium alloy into the desired shape at room temperature.
2. Secure it using specialized fixtures and heat it to 500°C for aging treatment.
3. Rapidly immerse it in water for quenching and cooling. The “set” nickel-titanium alloy will permanently retain this shape. When heated above its phase transformation temperature (Af), it will revert to its original shape.

THT has experience on different nitinol product, including nitinol plate, nitinol rod, nitinol tube, nitinol wire, nitinol ring, nitinol disc and special customized nitinol product, whatever super elastic or shape memory function, different Af or As temperature range, we could customize and give technical ideas about your nitinol usage, if any nitinol question or nitinol request, welcome to contact us.