How long does memory last? For shape memory alloys, the longer the better
(PHYSorg.com Chemistry)

Known to many as muscle wire or memory metal, shape memory alloys are materials that can be bent or deformed, and then return to their original shape when heat is applied. While people are most familiar with the material in `unbreakable` eye-glass frames, these alloys are also used as vibration dampers, actuators, and sensors in high technology applications like the aerospace and automotive industries, medical devices, and civil engineering.