shape memory, property possessed by certain alloys that allows them to return, when heated, to their original shape after having been deformed. This effect results because, as the alloy is deformed, it undergoes a martensitic (or athermal) transformation—a solid-state transition that rapidly changes the crystalline structure of the alloy without thermal activation—that is readily reversed once an appropriate amount of heat is applied. Among the alloys are copper-aluminum-nickel, copper-zinc-aluminum, nickel-titanium, and iron-manganese-silicon. Applications of shape memory include heat-activated fasteners, switches, eyeglass frames, orthopedic devices, teeth braces, and blood clot filters.