Nitinol or Nickel Titanium (also known as NiTi) is in the unique class of shape memory alloys. Nitinol shape memory alloys can be modified to a great extent by changes in composition, mechanical working, and heat treatment.

Nitinol transformation properties

 Transformation temperature    -200 to 110 deg. C
 Latent heat of transformation    5.78 cal/g
 Transformation strain
 (for polycrystalline material)
 for a single cycle  max 8% 
 for 100 cycles  6%
 for 100,000 cycles  4%
 Hysteresis    30 to 50 deg. C

 

Nitinol physical properties

 Melting point    1300 deg. C (2370 deg. F)
 Density    6.45 g/cu.cm (0.233 lb/cu.in)
 Thermal conductivity  austenite  0.18 W/cm * deg. C (10.4 BTU/ft * hr * deg. F)
 martensite  0.086 W/cm * deg. C (5.0 BTU/ft * hr * deg. F)
 Coefficient of thermal expansion  austenite   11.0E-6/deg. C (6.11E-6/deg. F)
 martensite  6.6E-6/deg. C (3.67E-6/deg. F)
 Specific heat    0.20 cal/g * deg. C (0.20 BTU/lb * deg. F)
 Corrosion performance    excellent

 

Electrical and magnetic properties

 Resistivity
 [resistance = resistivity *
 length / cross-sectional area] 
 austenite  approx. 100 micro-ohms * cm (39 micro-ohms * in)
 martensite  approx. 80 micro-ohms * cm (32 micro-ohms * in)
 Magnetic permeability     < 1.002
 Magnetic susceptibility    3.0E6 emu/g

 

Nitinol mechanical properties

 Young's modulus****  austenite  approx. 83 GPa (12E6 psi)
 martensite  approx. 28 to 41 GPa (4E6 to 6E6 psi)
 Yield strength  austenite  195 to 690 MPa (28 to 100 ksi)
 martensite  70 to 140 MPa (10 to 20 ksi)
 Ultimate tensile strength  fully annealed  895 MPa (130 ksi)
 work hardened  1900 MPa (275 ksi)
 Poisson's ratio   0.33
 Elongation at failure  fully annealed   25 to 50%
 work hardened  5 to 10%
 Hot workability    quite good
 Cold workability    difficult due to rapid work hardening
 Machinability    difficult, abrasive techniques preferred

 

Nitinol technical properties legend

**     Values listed are for a full martensite to austenite transition.
**     Hysteresis can be significantly reduced by partial transformation or ternary alloys.
***   Similar to 300 series stainless steel or titanium
**** Highly nonlinear with temperature

Loop of nitinol tubing

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