Nitinol
A nickel-titanium shape memory alloy
Typical values for the temper in the title
Nitinol is an alloy of nickel and titanium in nearly equal atomic amounts (about 55–56% nickel by weight). It has two special properties: shape memory, meaning a part deformed when cold returns to its original shape when heated, and superelasticity, meaning it can be strained several times more than an ordinary metal and returns to shape without permanent deformation.
Both properties come from a reversible change between two crystal structures, austenite and martensite. The transformation temperature is very sensitive to composition and processing. It is used in stents, orthodontic wires and medical devices, and also in actuators, eyeglass frames and seals.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 900 MPa | |
| Yield strength Rp0.2 | 200 MPa | transformation (plateau) stress, not ordinary yield |
| Elongation A | 8% | |
| Hardness | 230 HB | |
| Modulus of elasticity E | 83 GPa | austenite; lower in martensite |
| Density ρ | 6.45 g/cm³ | |
| Machinability | 5% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Ni nickel | about 55–56 (nominal) | sets the transformation temperature |
| Ti titanium | balance |
Nominal composition. Exact ranges for medical use are in ASTM F2063. A small change in nickel content shifts the transformation temperature.
Conditions and heat treatment
In Nitinol, heat treatment "teaches" the material the shape it will remember, and sets the transformation temperatures.
| Condition | Properties | When to choose it |
|---|---|---|
| Superelastic | transformation at or below body temperature | stents and medical wires |
| Shape memory | returns to shape on heating | actuators and mechanisms |
| Shape setting | heating the part on a fixture | "teaching" the shape |
Applications
- Stents and medical devices
- Orthodontic wires
- Actuators and sensors
- Eyeglass frames
- Seals and couplings
Fabrication
Welding
Welding mainly by laser, in a protected atmosphere. Conventional welding to other metals forms brittle compounds.
Machining
Nickel alloys work harden, stay strong when hot, and wear tools. Use low speed, a steady feed that does not "rub", sharp rigid tools and plenty of coolant.
Processing
Very hard to machine. Laser cutting, EDM and grinding are common.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| Ti-6Al-4V (Grade 5) | 950–1100 / 880 MPa | Good — ERTi-5 | ordinary titanium, without shape memory · material page |
| Elgiloy | 2070 / 1720 MPa | Laser / EBW | cobalt-chromium for medical springs · material page |
| 316 / 316L | 485–620 / 170–310 MPa | Excellent — ER316L | a medical stainless, cheap · material page |
Common mistakes
Treating the yield strength like an ordinary metal
The database value (200 MPa) is the transformation (plateau) stress, not ordinary yield.
Ordering without stating transformation temperatures
The material is defined mainly by its Af temperature, not only by composition.
Machining by conventional methods
The material work hardens and wears tools rapidly.
Equivalents, standards and supply
| ASTM | F2063 |
|---|---|
| Standards | ASTM F2063 / ISO 15841 |
| Forms | wire · sheet · pipe |
| Producers | Nitinol Devices · Fort Wayne Metals · NDC |
Learn more
Values are typical and for comparison only. For design, rely on the standard and the mill certificate. Sources: ASTM (B127, B164, B168, B443, B575, B619 and others), Special Metals and Haynes data sheets, and the METAL HUB materials database. Inconel and Monel are trademarks of Special Metals, and Hastelloy of Haynes International.
Updated: October 31, 2026