Nitinol is an alloy of Nickel and Titanium (NiTi)
TiME Process for Nitinol
The TiME process can produce Nitinol parts incorporating complex features and geometries. Thicknesses ranging from 25 µm to 1.0 mm can be processed.
Safer, non-HF Chemistry
Through a vigorous R&D programme, Advanced Chemical Etching has been able to develop safer, non-HF chemistry to etch Nitinol and other Titanium alloys.
No Altering the Chemical Makeup
Importantly, the process does not alter the mechanical and chemical properties of Nitinol, namely, its super-elasticity, shape memory and biocompatibility.
Shape Memory & Super-Elasticity
The Nitinol alloy can be shaped cold and ‘remembers’ its original shape and reverts to it when heated above the transformation temperature.
The Benefits of Nitinol Etching and the TiME Process
Shape memory is the effect of restoring the original shape of a deformed material by heating it.
Nitinol has a ‘rubber-like’ elasticity that creates a huge variety of possible usages.
Due to its composition and corrosion resistance, Nitinol is a biocompatible material that has found widespread use in a variety of medical applications.
Nitinol is an extremely versatile material and is used throughout the medical industry for stents, implants and medical devices.
Stress & Burr Free
Due to the usage of our TiME process, we are able to produce stress-free and burr-free Nitinol components.
There are also non-medical applications for Nitinol, such as in-temperature control where the shape memory of Nitinol can be utilised to activate a variable resistor or a switch. Nitinol is also used in mechanical watch springs and as an insert for golf clubs.
The Shape Memory Effect of Nitinol
- The shape-memory effect in NiTi was discovered in the early sixties at the US Naval Ordnance Laboratory (hence the name Nitinol).
Why does Nitinol have Shape Memory?
Nitinol can exist in two different solid structures: austenitic or martensitic. The austenitic crystal structure is highly ordered while the martensitic structure is less ordered and can be deformed quite easily. The ability of Nitinol to change its structure from austenitic to martensitic and vice versa gives Nitinol its shape memory and super-elasticity.
How does Shape Memory occur?
Above a certain temperature, called the transformation temperature, Nitinol exists in the high-strength austenitic phase, whereas below this temperature, the alloy is martensitic and can be easily deformed.
An Example of Shape Memory
For example, if a straight piece of Nitinol wire is deformed into a coil at a temperature below its transformation temperature, the coiled wire will spring back to its original shape once it is heated above the transformation temperature.
Shape Memory Put Simply…
The alloy ‘remembers’ its original shape and reverts to it when heated above the transformation temperature.
This shape recovery occurs over a temperature range of just a few degrees. This temperature window can be adjusted by slight variations in alloy composition and through heat treatment.
While the martensitic form of Nitinol normally exists below the transformation temperature, deformation at a temperature slightly higher than the transformation temperature can lead to the formation of some martensite.
Reverting of Form
As soon as the stress is removed, the martensite reverts immediately to the austenitic form that was present prior to the deformation. This gives Nitinol a characteristic ‘rubber-like’ elasticity.
BIOCOMPATIBILITY & CORROSION RESISTANCE
What is Biocompatibility?
Biocompatibility is the ability of a substance to be accepted by the body.
How does biocompatibility relate to Nitinol?
Nickel is present in different human tissues at very low concentrations (~ 0.1 ppm), but higher concentrations of nickel can be harmful. In Nitinol, nickel and titanium form an intermetallic compound; in other words, the nickel is converted into a compound and is therefore chemically locked.
As a result, there is no risk of nickel release from Nitinol implants into the body.
Corrosion Resistance of Nitinol
The corrosion resistance of Nitinol contributes to its biocompatibility. After an appropriate passivation treatment, the surface of Nitinol becomes covered by a titanium-rich oxide layer that is both stable and uniform. This surface oxide layer protects the bulk alloy from bio-corrosion and also creates a physical and chemical barrier against nickel oxidation.
Sustain Large Deformations
Research has also shown that this oxide film is able to sustain large deformations induced by the shape memory effect and that it is more resistant to chemical breakdown compared to the oxide film on passivated 316L stainless steel.