Nitinol is a specific example of which category of materials?

• A. Shape memory alloy
• B. Thermochromic ink
• C. Micro encapsulation
• D. Polymorph

Answer: (A)

Nitinol is a shape memory alloy. This means it can be deformed when it’s in one phase and then return to its original shape when heated, due to a reversible phase change between martensite and austenite within the metal. That memory effect—the ability to remember and revert to its initial form—comes from the way the crystal structure rearranges with temperature. In practical terms, NiTi can be bent or compressed and then spring back when warmed, which is why it’s used in devices like stents and orthodontic wires. The other options describe materials or concepts that don’t capture this metallic shape-changing behavior: thermochromic ink changes color with temperature, micro encapsulation is a packaging/encapsulation technique, and polymorph refers to different crystal forms of a material, not a metal’s shape-memory property.