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Seven Special Properties of Nitinol Shape Memory Alloy

wallpapers News 2020-05-07
Nitinol is a shape memory alloy. Shape memory alloy is a special alloy that can automatically restore its plastic deformation to its original shape at a certain temperature and has good plasticity. 

Nitinol is a shape memory alloy. Shape memory alloy is a special alloy that can automatically restore its plastic deformation to its original shape at a certain temperature. Its expansion rate is more than 20%, its fatigue life is 1 * 10 to the 7th power, its damping characteristics are 10 times higher than ordinary springs, its corrosion resistance is better than the best medical stainless steel at present, so it can meet all kinds of engineering and Medical application needs are a very good functional material.

In addition to its unique shape memory function, memory alloys also have excellent characteristics such as wear resistance, corrosion resistance, high damping and super elasticity.

Special properties of Nitinol

1. Shape memory
shape memory is when a certain shape of the parent phase is cooled from above Af temperature to below Mf temperature to form martensite, then the martensite is deformed at a temperature below Mf and heated to below Af temperature With the reverse phase change, the material will automatically restore its shape in the parent phase. In fact, the shape memory effect is a heat-induced phase transformation process of nickel-titanium alloy.

2. Super-elasticity
The so-called super-elasticity refers to the phenomenon that the specimen produces a strain much larger than its elastic limit strain under the action of external force, and the strain can automatically recover when unloaded. That is, in the state of the parent phase, due to the effect of external stress, the stress-induced martensite transformation occurs, so that the alloy exhibits a mechanical behavior different from that of ordinary materials. Law.Compared with shape memory properties, superelasticity does not involve heat. In a word, superelasticity means that the stress does not increase with the increase of strain within a certain deformation range. Superelasticity can be divided into linear superelasticity and nonlinear superelasticity. The stress-strain curve in the former is close to a linear relationship between stress and strain. Non-linear superelasticity refers to the results of stress-induced martensitic transformation and its inverse phase transformation during loading and unloading in a certain temperature range above Af.

3. Sensitivity of temperature changes in the oral cavity:
 The curative power of stainless steel wire and CoCr alloy orthodontic wire is basically not affected by the temperature in the oral cavity. The orthodontic power of superelastic nickel-titanium alloy orthodontic wire changes with the change of oral temperature. When the amount of deformation is constant. As the temperature rises, the correction power increases. On the one hand, it can accelerate the movement of teeth, because the temperature changes in the oral cavity will stimulate the blood flow in the stagnation of blood flow caused by the correction device, so that the repair cells are fully nourished during the movement of the teeth Maintain its vitality and normal function. On the other hand, orthodontists cannot accurately control or measure the correction power in the oral environment.

4. Corrosion resistance:
Some studies have shown that the corrosion resistance of nickel-titanium wire is similar to that of stainless steel wire.

5. Anti-toxicity:
The special chemical composition of nickel-titanium shape memory alloy, that is, it is a kind of nickel-titanium and other atomic alloys, containing about 50% nickel, and nickel is known to have carcinogenic and cancer-promoting effects. In general, the titanium oxide on the surface layer acts as a barrier to make Ni-Ti alloys have good biocompatibility. TiXOy and TixNiOy of the surface layer can suppress the release of Ni.

6. Soft orthodontic power:
The currently used orthodontic metal wires include austenitic stainless steel wire, cobalt-chromium-nickel alloy wire, nickel-chromium alloy wire, Australian alloy wire, gold alloy wire and ß titanium alloy wire. The load-displacement curve of these orthodontic correction wires under tensile test and three-point bending test conditions. Nitinol's unloading curve platform is the lowest and flattest, indicating that it can provide long-lasting and gentle healing power.

7. Good shock absorption characteristics:
the greater the shock to the archwire caused by chewing and nocturnal teeth, the greater the damage to the roots and periodontal tissues. Through the results of different arch wire attenuation experiments, it is found that the vibration amplitude of the stainless steel wire is larger than that of the superelastic nickel-titanium wire. The initial vibration amplitude of the superelastic nickel-titanium arch wire is only half that of the stainless steel wire. The health of teeth is very important, and traditional arch wire, such as stainless steel wire, has a tendency to increase the absorption of tooth roots.

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