Nickel Titanium (also known as Nitinol) belongs to materials known as shape memory alloys. As a result in temperature change there is a thermoelastic martensitic phase transformation in the NiTi that is responsible for its properties such as shape memory effect, superelasticity, and high damping capability. Change / modification in the composition of the two metals and also different heat treatment. In most cases a trial and error process is required to optimize these factors for a particular application.
One such application is vascular stents to reinforce blood vessels in the human body.

Do you know if they are used in cardial stents?