nitinol shape memory alloy has the ability to restore shape after appropriate heat treatment, which is called shape memory effect (SME). Shape memory effect can be divided into one-way shape memory effect, two-way shape memory effect and Full memory effect.
In the state of low-temperature martensite, the shape of high-temperature phase will be restored when heating, and the shape of low-temperature phase will not be restored when cooling.
Restore the shape of high-temperature phase during heating and low-temperature phase during cooling, that is, spontaneously and reversibly restore the shape of high-temperature and low-temperature phase through temperature rise and fall.
The shape memory alloy is deformed when subjected to external forces, and returns to its original state after removing the external forces. This phenomenon is called superelasticity. When the superelastic deformation of the shape memory alloy occurs, martensite transformation is induced,and the reverse martensite transformation occurs after removing the external force.
Shape memory alloy has good damping characteristics due to the self coordination of martensitic transformation and various interfaces (twin surface, phase interface and variant interface) and interface movement formed in martensite.
For Ni Ti alloy with initial microstructure of martensite, there is a linear relationship between resistance and strain in the tensile process; For Ni Ti alloy whose initial structure is austenite or a mixture of austenite and martensite, when stress-induced martensitic transformation occurs, the slope of the curve decreases, and the resistance strain relationship remains linear before and after transformation。