Shape-Memory Alloys

Objective: to demonstrate how the motion of atoms under added heat can change the shape of metals Description: · During this demonstration, a nanoscale change is impacting the macroscale. · Shape-memory alloys return to their original shape when heated, while other alloys do not. · Nitinol wire, a shape-memory alloy, will be subjected to heat treatment. · Steel wire will also be subjected to heat treatment. · The behavior of the two wires will be compared and the mechanisms behind each behavior will be discussed.

·Nitinol is a nickel-titanium alloy (~50%Ni,~50% Ti) that has two phases ◊high-temperature phase: austenite ◊low-temperature phase: martensite · When deformed at a low temperature and then heated, nitinol will return to the shape established at the high temperature as the atoms rearrange themselves back to their high-temperature positions.

Joana Sousa
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