What’s so special about Nitinol?

 We chose to use a nitinol sobstrate material for our research because of the material’s superelastic properties.  Nitinol can be strained to just over 5% without experiencing any permanent deformation.  Most metals can be strained to less than 1% before experiencing permanent shape change (plastic, or permanent deformation).  As our research focuses on the properties of stretched thin films, it was important for us to find a material that could be stretched.

Nitinol also exhibits a shape memory property, which is why it is sometimes referred to as a shape memory alloy, or SMA.  Although for our experiments we are not using nitinol in its shape memory phase, it is an interesting characteristic. 

Nitinol’s super-elastic phase is called the “austenite” phase.  The crystal structure in this phase is body centered cubic, as shown in the pictures on the left.

Nitinol’s shape memory phase is martensitic, often referred to as the martensite phase (but many alloys are martensitic).  In this phase, the crystal structure of the material is slanted.