Nitinol is a kind of shape memory alloy, which 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, which 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%, damping characteristics are 10 times higher than ordinary springs, and its corrosion resistance is better than the best medical stainless steel at present, so it can meet the needs of various engineering and medical applications. It is a very excellent functional materials.
In addition to the unique shape memory function, the memory alloy also has excellent characteristics such as wear resistance, corrosion resistance, high damping and super elasticity.
Special properties of Nitinol Powder
1. Shape memory characteristics (shape memory) Shape memory is when the parent phase of a certain shape is cooled from above Af temperature to below Mf temperature to form martensite, 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 thermally induced phase transformation process of Nitinol.
2. Superelasticity The so-called superelasticity refers to the phenomenon that the sample produces a strain much larger than its elastic limit strain under the action of external force, and the strain can automatically recover when unloaded. Compared with shape memory properties, superelasticity has no thermal involvement. 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. Nonlinear superelasticity refers to the result of stress-induced martensitic transformation and its reverse phase transformation during loading and unloading in a certain temperature range above Af. Therefore, nonlinear superelasticity is also called phase transformation pseudoelasticity. The phase change pseudo-elasticity of Nitinol can reach about 8%.
3. Sensitivity to temperature changes in the oral cavity: the orthodontic power of stainless steel wire and CoCr alloy orthopedic wire is basically not affected by the temperature in the oral cavity. The corrective force of the super-elastic nickel-titanium alloy orthopedic wire changes with the change of the oral cavity temperature. When the amount of deformation is constant. As the temperature rises, the corrective force increases. On the one hand, it can accelerate the movement of teeth. This is because temperature changes in the oral cavity will stimulate the blood flow at the stagnant blood flow caused by the orthodontic device, so that the repair cells are fully nourished during the tooth movement. Maintain its vitality and normal function. On the other hand, orthodontists cannot precisely control or measure the orthodontic force in the oral environment.
4. Corrosion resistance: studies have shown that the corrosion resistance of nickel-titanium wire is similar to that of stainless steel wire.
5. Anti-toxicity: Nitinol shape memory alloy has a special chemical composition, that is, it is an atomic alloy such as nickel-titanium, containing about 50% nickel, and nickel is known to have carcinogenic and cancer-promoting effects. Under normal circumstances, the surface layer of titanium oxide acts as a barrier, so that Ni-Ti alloy has good biocompatibility. TiXOy and TixNiOy in the surface layer can inhibit the release of Ni.
6. Gentle orthodontic power: currently commercially used orthopedic wires include austenitic stainless steel wires, cobalt-chromium-nickel alloy wires, nickel-chromium alloy wires, Australian alloy wires, gold alloy wires and ß-titanium alloy wires. Regarding the load-displacement curves of these orthodontic wires under tensile test and three-point bending test conditions. The unloading curve platform of Nitinol is the lowest and the flattest, indicating that it can provide the most durable and soft correction force.
7. Good shock absorption characteristics: The greater the vibration caused by chewing and night molars to the arch wire, the greater the damage to the root and periodontal tissues. Through the results of different arch wire attenuation experiments, it is found that the vibration amplitude of stainless steel wire is larger than that of super-elastic Ni-Ti wire. The initial vibration amplitude of super-elastic Ni-Ti arch wire is only half of that of stainless steel wire. The health of teeth is very important, and traditional arch wires, such as stainless steel wires, tend to increase root resorption.
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