1. Nitinol shape memory alloy characteristics
Shape memory is when the parent phase of a certain shape is cooled from above the Af temperature to below the Mf temperature to form martensite, the martensite is deformed at a temperature below Mf, and after heating to below the Af temperature, the material will automatically recover with the reverse phase transformation. Its shape in its mother phase. In fact, the shape memory effect is a thermally induced phase transformation process of nitinol alloys.
2. Super elasticity
The so-called superelasticity refers to the phenomenon that the specimen produces a strain far greater than the elastic limit strain under the action of external force, and the strain can automatically recover when unloaded. That is, in the parent phase state, due to the action of external stress, stress-induced martensite transformation occurs, so the alloy exhibits mechanical behavior different from ordinary materials. Its elastic limit is much larger than that of ordinary materials, and it no longer obeys Hu Gram's law.
In contrast to shape memory properties, superelasticity has no thermal involvement. All in all, superelasticity means that the stress does not increase with the increase of strain within a certain deformation range. Superelasticity can be divided into two categories: linear superelasticity and nonlinear superelasticity. In the stress-strain curve of the former, the relationship between stress and strain is close to linear. Nonlinear superelasticity refers to the result of stress-induced martensitic phase transformation and its reverse phase transformation respectively during the loading and unloading processes within a certain temperature range above Af. Therefore, nonlinear superelasticity is also called phase transformation pseudoelasticity.
The phase transition pseudoelasticity of nickel-titanium alloy can reach about 8%. The superelasticity of nickel-titanium alloys can change with changes in heat treatment conditions. When the archwire is heated above 400oC, the superelasticity begins to decrease.
3. Sensitivity to temperature changes in the oral cavity
The orthodontic power of stainless steel wire and CoCr alloy dental orthodontic wire is basically not affected by the temperature in the oral cavity. The orthodontic force of superelastic nickel-titanium alloy dental orthodontic wire changes with changes in oral temperature.
When the deformation amount is constant. As the temperature rises, the correction force increases. On the one hand, it can accelerate the movement of teeth, because the temperature change in the oral cavity will stimulate the blood flow in the areas where the blood flow is stagnant due to capillary stagnation caused by the orthodontic device so that the repair cells are fully nourished during the movement of the teeth. Maintain its vitality and normal functions. Orthodontists, on the other hand, cannot precisely control or measure orthodontic forces in the oral environment.
4. Anti-corrosion performance
Studies have shown that the corrosion resistance of nitinol wire is similar to that of stainless steel wire.
5. Anti-toxicity
The special chemical composition of nitinol shape memory alloy is that it is a nickel-titanium atomic alloy containing about 50% nickel, and nickel is known to be carcinogenic and cancer-promoting. In general, the surface layer of titanium oxidation acts as a barrier, making Ni-Ti alloys have good biocompatibility.
The TiXOy and TixNiOy in the surface layer can inhibit the release of Ni.
6. Gentle correction power
Currently, commercially used orthodontic wires include austenitic stainless steel wire, cobalt-chromium-nickel alloy wire, nickel-chromium alloy wire, Australian alloy wire, and titanium alloy wire. Load-displacement curves of these orthodontic wires under tensile test and three-point bending test conditions.
The unloading curve platform of nickel-titanium alloy is the lowest and flattest, indicating that it can best provide long-lasting and gentle correction force.
7. Good shock absorption characteristics
The greater the vibration caused by chewing and grinding teeth to the archwire, the greater the damage to tooth roots and periodontal tissues. Through the results of different archwire attenuation experiments, it was 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 archwire is only half of that of the stainless steel wire. The good vibration and shock-absorbing characteristics of the archwire are good for The health of teeth is very important, and traditional archwires such as stainless steel wires tend to aggravate tooth root resorption.
Xi'an Zhanwo Metal Material possesses advanced capabilities and expertise to serve as a professional, high-quality supplier of nitinol shape memory alloy products for global customers.
