The so-called shape memory alloy refers to the general name of the alloy that is plastically deformed at a certain temperature and then heated at a high temperature to return to its original state. This new functional material can be used in automatic machinery, robots, heat engines, air conditioning equipment and other parts.

In addition to nickel-titanium alloy, about 20 kinds of alloys, such as copper, zinc, gold, cadmium, nickel and aluminum, have been found, among which NT alloy has the best "memory". Therefore, most people think that metal alloys have shape memory characteristics because they contain metal element: nickel.

In fact, the principle of memory alloy is not very clear.