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Product Datasheetnitinol
General InformationNitinol exhibits a unique phase transformation in the crystal structure when transitioning between the Austenite and Martensite phases. The Austenite phase being the high temperature, stronger state compared to the weaker, low temperature Martensite phase. The most common two terms used to describe this behavior are "Superelasticity" and "Shape Memory". Shape Memory occurs when a material is in its Martensitic (low temperature) phase and is deformed to a new shape. When the material is then heated above the Af temperature it changes back to Austenite and the deformation is lost as the material returns to its pre-deformed, original shape. Up to 8% shape recovery is possible.
All nitinol exhibits BOTH superelastic and shape memory behavior. Alloy composition and the material's thermo-mechanical processing history dictate the temperatures where these properties exist. Austenite: Nitinol's stronger, higher temperature phase. Crystalline structure is body-centered cubic. Superelastic behavior is in the phase (over a 50-60C temperature spread). Martensite: Nitinol's weaker, lower temperature phase.
Crystalline structure is twinned. Material easily deformed in this phase. Once deformed in martensite it will remain deformed until heated to austenite where it will return to its pre-deformed shape, i.e. "shape memory" effect.
PrecautionsThese values should only be used as guidelines for developing material specifications. Properties of Nitinol Alloys are strongly dependent on processing history and ambient temperature. The mechanical and superelastic properties shown here are typical for standard superelastic straight tubes at room temperature tested in uniaxial tension. Bending properties differ, and depend on specific geometries and applications. Modulus is dependent on temperature and strain.
Chemical Composition53.5Ni-45Ti-1.5Fe
Name of ManufacturerNitinol Devices & Components
47533 Westinghouse Drive
Fremont, California 94539
Fax: (510)683-2001
Specific Gravity6.5
Phase changes-200 to 110 °C
Remark: Transformation Temperature
Magnetic PropertiesNonmagnetic
Tensile Modulus41 to 75 GPa
Remark:Low value for martensite phase, while high value for austenite phase
Poisson Ratio0.33
Electrical Volume Resistivity7.6e-7 to 8.2e-7 ohm.m
Thermal Expansion Coefficient6.6 to 11 μstrain/°C
Remark:Low value for martensite phase, while high value for austenite phase
Melting Range1300 °C
MachinabilityNitinol is a very abrasive material to machine due to its tough titanium oxide surface. Milling, turning, grinding are possible with excellent results but expect a lot of tool wear. Carbide tooling is highly recommended. During centerless grinding ensure adequate cooling lubricant is present. Nitinol can be EDM, water jet cut, and laser machined with excellent results.
WeldingWelding nitinol to itself is usually very effective if the weld is protected by an inert atmosphere and the heat effected zone is minimized. Laser, TIG, and resistance welding are all processes that have been successful. Nitinol welded to dissimilar metals, such as stainless steel, does not give acceptable results since the outcome is a brittle intermetallic interface which cannot be stress relieved.
BrazingBrazing can only be accomplished after re-inforcement and plating
SolderingNitinol's tough oxide layer does not promote good solder wetting. An aggressive flux (Indium Corp. #2 flux) is required to remove the oxide, then a standard Sn-Ag solder can be used to attain good results.
Thermal CyclingThermal cycling both with or without applied load can result in degradation, such as shift in transformation temperature, reduction in available strain, changes in reset force and even to fracture.
Special RecommendationsNitinol can be bonded to other materials using epoxies and adhesives. Mechanical techniques such as crimping and swaging are possible. Another mechnical technique is to use nitinol's shape memory or superelastic properties to join materials. A nitinol tube connector can be expanded either mechanically or by cooling it to martensite than deforming it, inserted over another element, than allowing the connector to return to austenite and clamp down on the element. (cryofit connector)