Thermodynamics > Changes of State DCS# 4C45.15

SHAPE MEMORY OF NITINOL WIRE

samples of nitinol wire

APPARATUS
nitinol wire samples 202-11-E1
beaker of hot water (>30-50° C)  101-01-C
or heat gun 202-11-A
liquid nitrogen Sci Ctr dock
document camera
202

DESCRIPTION
Use the overhead projector to show the shape of a piece of nitinol wire.  Bend the wire.  When heated, wire returns to its original shape.

Cool the super-elastic wire in liquid nitrogen.  Deform the wire.  Allow it to return to room temperature and it will return to its original shape.


NOTES


Nitinol wire undergoes a solid-solid phase transition between the low-temperature "martensite" form in which the wire is easily deformed and the higher temperature "austenite" form in which the wire is rigid and springy.

We have samples made of two different nitinol alloys that differ in the percent composition of nickel and titanium and in their transition temperatures, so that one is in the martensite phase and the other in the austenite phase at room temperature.

The shape memory metal has a transition temperature of 55° C.
The super elastic samples have a transition temperature of 14° C.

 
REFERENCES
 
Teaching General Chemistry:  A Materials Science Companion, Arthur B. Ellis et al. 1993 American Chemical Society.

http://www.sma-inc.com/

Sci. Am., Nov. 1979.