Memory metal is a kind of clock alloy, which can be made into a certain shape at a lower temperature, and then can be changed back to its original shape after heating, so it has memory, so we call it "memory metal".

Memory metal, a straight wire is bent at a right angle (90), and once it is loosened, it will recover a little to form an angle greater than 90. To straighten the bent wire, it must be folded 180 before it is loosened, so that it can just return to the straight line.

For example, the crystal structure of Ni-Ti alloy is different above 40℃ and below 40℃, but when the temperature changes around 40℃, the alloy will shrink or expand, thus changing its morphology. Here, 40℃ is the "metamorphic temperature" of NiTi memory alloy. All kinds of alloys have their own abnormal temperatures.

The deformation temperature of the above superalloys is very high. It is made into spiral shape at high temperature and is in a stable state. When forcibly straightened at room temperature, it is in an unstable state. So as long as it is heated to an abnormal temperature, it will immediately return to the original stable spiral shape.

Extended data:

The high temperature phase of shape memory alloy has a high degree of structural symmetry, usually with an ordered cubic structure. Below the temperature of Ms, the single-oriented high-temperature phase transforms into martensite variants with different orientations.

When this material is deformed below Ms temperature to make a component, the martensite variants that are not conducive to the stress direction in the material are decreasing continuously; People in a favorable position keep growing. Finally, it is transformed into an element of ordered martensite with a single orientation.

If it is heated above the As point, the unidirectionally oriented martensite with low symmetry will be reversed to form the previously unidirectionally oriented high temperature phase.

Corresponding to this reversible transformation of microstructure, the macroscopic shape of materials at high temperature is restored, which is called one-way shape memory. When the memory element treated by a certain process is cooled below Ms, it can recover its shape at low temperature, which is called bidirectional shape memory effect.

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