How do shape memory alloys respond when heat is applied?

Shape memory alloys (SMAs) exhibit a unique property known as the shape memory effect. When heat is applied, these alloys can change from a deformed shape back to their original, pre-defined configuration. This transformation occurs because of a phase change in the material at certain temperatures.

Upon heating, the SMA transitions from a martensitic phase (which is stable at lower temperatures and allows for deformation) to an austenitic phase (which is stable at higher temperatures and maintains the original shape). As a result, they bend when stressed but, upon heating, they return to their original shape. This behavior is a key characteristic of SMAs and is utilized in various applications, such as in actuators and medical devices, where controlled movement is required.

This characteristic distinctly differentiates SMAs from other materials that might become brittle, maintain their shape regardless of stress, or melt under high temperatures, as those responses do not demonstrate the unique capacity for reversible deformation associated with shape memory alloys.