News 07. 04. 26:Titanex: Freunde der Technik in Bäretswil - 8. Mai
Request a QuoteStay competitive! Through Delivery Time, Quantity and Price!
Download
Titanex' stocklists (Ti)Anfrage / Bedarf
Steigern Sie Ihre Wettbewerbsfähigkeit! Durch Lieferzeit, Menge und Preis!
Titanex' Lagerlisten holen!
PDF downloads» Nickel-Titanium - Shape Memory Alloys
Standard binary (50/50), high nickel (approx. 55 - 56%), chrome or iron dope versions are in stock at the mill. For further redrawing.
Shape Memory Alloy (SMA) or also called Nitinol in continuous lengths on spools, in straight and cut lengths, rolled flat wire can be supplied. For flat wires the ration for thickness to width sahll remain within 10 x 1. Turksheaded for orthodontic arch wires, strands and cables also available.
Wires can be supplied from .060" down to .001" (1.52 down to 0.025 mm).
- Shape memory devices recover a particular shape upon heating above their transformation temperatures
- Shape Memory involves the continuous appearance and disappearance of martensite with rising and falling temperature.
- Upon transformation Shape Memory Alloys undergo a solid-to-solid phase transformation, from martensite to austenite upon heating, and in reverse upon cooling
- Shape memory actuation devices can act without constraint to freely recover their trained shape, can be fully constrained so that they provide a force, or can be partially constrained so that they perform work.
» Applications
- Medical Industry and Technology
- Bendable surgical tools
- Implants (stents, joints, clamps, etc.)
- Bone suture anchors
- Orthodontic wires
- Space and Aviation Industry
- Flexible satellite antennas
- Satellite release bolts
- Automotive Industry
- Actuators for thermal compensation
- Flexible mechanical connection
- Other Applications
- Coffeepot thermostats
- Micro-actuated latch mechanisms
- Pipe coupling
- Highly flexible and robust eyeglass frames
» Crystal Structure
The austenite or parent P phase of NiTi is an ordered CsCl B2 structure. Martensitic NiTi has a B19’ monoclinicstructure
NiTi in its austenite phase shows seemingly plastic deformations that are fully recoverable when the applied stress is removed. The pseudoelastic effect is due to a stress-induced martensitic transformation. That is at temperatures above Af applied stress lowers the elastic strain energy in equation 1.2, and induces a P® M transformation. When stress is removed the transformed martensite reverts back to the austenite phase providing the shape recovery.
» Two way effect
To achieve the two-way effect a biasing force is required to reshape the NiTi when cooled. Kuribayshi introduced this biasing force by tailoring precipitates in his films such that there were compressive and tensile stresses on opposite sides of his film. The film curled when in the martensitic phase and when heated to the austenite phase flattened because the higher modulus overcomes the residual stresses.
MS Thesis of Ken K. Ho "Sputter deposition of NiTi SMA for MEMS Application" (1997)
» Melt Practice
Nitinol is a family of alloys which are comprised of near equiatomic percentages of nickel and titanium. A few variants of Nitinol also include small amounts of a third element that is used to alter certain properties. Nitinol exhibits a thermoelastic martensitic transformation. This transformation is responsible for either shape memory or superelasticity being exhibited by the alloy. Following deformation below the transformation range, the ability called shape memory allows recovery of a predetermined shape upon heating above the transformation range. Super-elasticity is the ability to recover a shape upon removal of an applied stress over a narrow range of deformation temperatures.
The strain recovered with shape memory or superelasticity provides nearly ten times the elastic springback of other alloys such as stainless steel.
| Nickel |
54.5-57.0 wt. % |
| Carbon |
0.050 wt % Max. |
| Oxygen |
0.050 wt % Max. |
| Hydrogen |
0.005 wt % Max. |
| Titanium |
Balance |
|
Austenite |
Martensite |
|
| Density |
6.45 g/cm 3 |
6.45 g/cm 3 |
| Modulus of Elasticity |
75 GPa |
40 GPa |
| Electrical Resistivity |
82 x 10-6 ohm-cm |
76 x 10-6 ohm-cm |
| Magnetic Susceptibility |
3.7 x 10-6 emu/g |
2.4 x 10-6 emu/g |
| Coefficient of Thermal Expansion1 |
1 x 10-6/°C |
6.6 x 10-6/°C |
» Transformation Properties
Because shape memory and superelasticity are very temperature dependent, there are a number of thermal points of interest that deserve discussion in order to gain an understanding of the material. This paper will discuss two of these points: the fully annealed austenitic peak and the active austenitic finish temperatures. The fully annealed austenitic peak (Ap) is a temperature that is used in order to classify the types of Nitinol. Several companies will make use of different points, but the intent of the measurements are the same. The Ap is the point that the fully annealed Nitinol has the highest rate of transformation from Martensite to Austenite. The active austenitic finish temperature (Active Af ) is a finished material property that is measured after heat treatment. This is the temperature at which the material has completely transformed to Austenite, which means that at and above this temperature the material will have completed its shape memory transformation or will display its superelastic characteristics. For a more detailed discussion of thermal properties and the effect that they may have on your finished product, please feel free to contact us.
| Fully Annealed Austenitic Peak (Ap) by Differential Scanning Calorimeter |
-25 to -5 °C |
| Active Austenitic Finish (Af) by bend and free recovery |
10 to 20 °C |
» Surface Finishes
- Black Oxide: Shiny Black oxide.
- Dark Oxide: Ranging from a Dark Gray to Black color.
- Light Oxide: Ranging from Gold to Light Brown colors.
- Etched: Material with the Oxide chemically removed, surface can be smooth to rough depending on your needs.
- Polished: Material has the Oxide chemically removed, the surface will appear smooth to the naked eye with a bright luster that is nearly as bright as Stainless Steel.
» Mechanical Properties
(at 21 +/- 3°C)
Two critical characteristics unique to Nitinol in the austenitic phase are the loading plateau and the unloading plateau. The loading plateau stress is the stress level at which material at a specific temperature above A f will force Austenite phase into Martensite. This produces an almost constant stress level over a relatively large range of strain, up to about 8%. The unloading plateau stress is the stress level at which the Martensite will return to the Austenitic phase.
Typical Tensile Curve for Nitinol Wire at T > Active Af
| Loading Plateau Stress (at 4% Strain) |
75kpsi. |
| Unloading Plateau Stress (at 4% Strain) |
35kpsi. |
| Permanent Set (after 6% Strain) |
0.25% |
| Permanent Set (after 8% Strain) |
0.50% |
| Ultimate Tensile Strength |
> 190kpsi |
| Elongation to Failure (as drawn) |
5.0% approx |
| Elongation to Failure (after 500°C Treatment) |
> 11% |
» Typical Applications
Nitinol wire is used in a variety of medical device applications including guidewires, catheters, stents, filters, needles, guide pins, orthodontic appliances, endodontic files, stone retrieval baskets and stylets. Other commercial applications include eyeglass frames, cellular phone antennae and fishing tackle.
