Structure of Nitinol - Heanjia Super-metals Co., Ltd.

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Structure of Nitinol

The combination of Nickel and Titanium is called nitinol that is a metallic alloy consisting of two metals in random percentages. This alloy exhibits two similar and unique features like shape and super flexibility that is also called pseudoelasticity. The shape memory of nitinol wire recommends the ability of nitinol to bear with the deformations at certain temperature then re-obtain its original shape. The superelasticity property can be obtained at the tapered temperature limit more than the transformation temperature of alloy such that no heating is required to enable the alloy to regain its shape and the alloy obtains extreme elasticity.

The name nitinol is kept due to its superior combination of metals showing extraordinary properties. Its special properties are obtained from the revocable solid state alteration that is called martensitic alteration held between two dissimilar crystallize materials that need to be pressed by 10,000–20,000 psi or 69–140 MPa of mechanical stress.

When Nitinol is kept at elevated temperatures, it exhibits an interpenetrating primal crystallized structure called as austenite. While under the lower temperatures, the alloy itself changes to more complex crystalline structure called as martensite. The specialized temperature under which the austenite changes to martensite is called as the transformation temperature. Particularly there are four types of transformation temperatures. When nitinol is completely austenite, the martensite starts to change in the alloy cools down to known as the martensite beginning that is M_s temperature. Further the temperature at which the transformation is finished is known as the M_f temperature. As soon as the alloy achieves complete martensite state it is sent for heating then the austenite state starts to produce that is called A_s temperature and when the austnite state is fully obtained it is called A_f temperature.

The periodic heating and cooling of nitinol alloy shows thermal hysteresis nature. The width of hysteresis vitally depends upon the accuracy of nitinol constituents and mechanism and its ordinary value lies in 20 degree C to 50 degree C.

The essential nitinol properties are two principles of its alternation. First is reversible alternation that upon heating at temperature more than the alternation criteria reverses the crystalline structure to the ordinary austenite form. Second is the alternation in both directions is made instantly.

The crystalline structure of Martensite has an excellent capability to show restricted unevenness in few manners without breaking the bonds between the metallic atoms. Such kind of deformation is called twinning that features with the reorganization of atomic planes though avoiding slip or stable distortion. It is capable to go through 6% to 8% strain in such way. However when the martensite is reversed to austenite by heating, the actual austenitic configuration is regained irrespective of the distortion of martensite phase.

Thus the word shape memory demonstrates the fact that the shape of the high temperature of austenite stage is memorized in fact the alloy is extremely distorted at the cold temperature.

Alarge amount of force can be generated by restricting the reverse action of distorted martensite to austenite. The common reason that for nitinol wire it is very tough to regain its actual configuration is it's the specialty of this alloy due to which it is called as intermetallic compound.

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