The principle and classification of memory metal

Principle of Memory Metal:

Memory metals mainly use the law that the crystal structure of certain alloys changes with temperature in the solid state. For example, Nitinol alloys have different crystal structures at temperatures above 40 degrees and below 40 degrees. However, if the temperature changes up and down 40 degrees, the alloy will shrink or expand, and produce changes in morphology, so 40 degrees is the transformation temperature of Nitinol. In fact, various alloys have their own transformation temperature. We can make the alloy into a certain shape at high temperature to make it in a stable state, then force it to straighten and make it in an unstable state at room temperature, and finally heat it to the metamorphic temperature to return to the shape of the stable state.

Features of memory metal:

(1) Large bending range and high plasticity.

(2) When the temperature reaches above the memory temperature, it can return to its previous shape.

(3) According to the alloy type, when the temperature reaches a certain value, the crystal structure inside the material will change, which will further lead to the change of the external morphology.

Memory metal classification:

(1) One-way memory effect

The memory metal can be deformed at lower temperatures and can return to its previous shape after heating. This kind of shape memory phenomenon only exists during the heating process, which is called the one-way memory effect.

(2) Two-way memory effect

Some memory metals can restore the shape of the high temperature phase when heated, and can restore the shape of the low temperature phase when cooled. This change is called the two-way memory effect.

(3) Full memory effect

This kind of memory metal is very special. When heated, it can recover the high-temperature phase shape, and when cooled, it becomes the low-temperature phase shape with the same shape but opposite orientation. This is called the global memory effect.

As far as the current memory metal market is concerned, shape memory metals that have been successfully developed include copper-based shape memory alloys, TiNi-based shape memory alloys, and iron-based shape memory alloys.