Shape-memory alloys are metallic materials that

Position 1: Ongoing research aims to broaden the working temperature range of these alloys so that they remain functional in more extreme engineering environments.

Position 2: This behaviour arises from a reversible solid-state phase transformation between two crystal structures known as austenite and martensite.

Position 3: Nickel-titanium alloys, commercially known as Nitinol, are the most widely used examples and have found applications in medical stents, orthodontic wires, and aerospace actuators.

Position 4: Shape-memory alloys are metallic materials that can return to a predetermined shape after being deformed, provided they are subjected to an appropriate thermal or stress stimulus.

Position 5: In the martensitic phase, the alloy is relatively soft and can be reshaped with modest force, whereas heating it above a transition temperature restores the stiffer austenitic structure and the original geometry.