current location：
What are the physical properties and uses of nitinol superelastic memory alloy?
features
1. Shape memory refers to the deformation of martensite below MF after cooling the parent phase of a certain shape from AF to MF. When heated to Af temperature, the shape of the parent phase will be restored automatically by reverse phase transformation. In fact, the shape memory effect is the thermally induced phase transformation of NiTi alloy.
2. Hyperelasticity refers to the phenomenon that the strain of the sample under the action of external force is much larger than that of the elastic limit strain, which will recover automatically when unloading. In other words, in the parent phase state, stress-induced martensitic transformation occurs due to the effect of applied stress. Therefore, the alloy exhibits different mechanical properties from ordinary materials, and its elastic limit is far greater than that of ordinary materials, and Hooke's law is no longer followed.
Compared with shape memory properties, hyperelasticity does not involve heat. In a word, hyperelasticity means that the stress will not increase with the increase of strain in a certain range of deformation. Hyperelasticity and hyperelasticity can be divided into hyperelasticity and hyperelasticity. In the stress-strain curve of the former, the stress and strain are almost linear. Nonlinear hyperelasticity refers to the results of martensitic transformation and its inverse transformation caused by stress during loading and unloading in a specific temperature range higher than AF. Therefore, nonlinear hyperelasticity is also called phase transition pseudo elasticity.
The pseudo elasticity of nitinol can reach about 8%. The hyperelasticity of nitinol alloy can be changed with the change of heat treatment conditions. When the wire is heated above 400 ℃, the hyperelasticity begins to decrease.
3. Sensitivity of temperature changes in the oral cavity: the orthodontic ability of stainless steel wire and CoCr alloy orthodontic wire is basically not affected by oral temperature. The orthodontic ability of hyperelastic nitinol dental floss changes with the change of oral temperature.
When the deformation is constant. The orthodontic ability increased with the increase of temperature. On the one hand, it can accelerate the movement of teeth, because the temperature change in the mouth will stimulate the blood flow in the stagnant area caused by capillary stagnation caused by the correction device, so that the repair cells need to obtain sufficient nutrition to maintain their vitality and normal function. On the other hand, orthodontists cannot accurately control or measure orthodontic ability in the oral environment.
4. Corrosion resistance: the research shows that the corrosion resistance of NiTi wire is similar to that of stainless steel wire.
5. Toxicity resistance: the special chemical composition of NiTi shape memory alloy is that it is a NiTi and other atomic alloys containing about 50% nickel, which is known to induce and promote AI. In general, the act surface layer is used as a barrier layer in titanium oxide, which makes Ni Ti alloy have good biocompatibility.
TixOy and tixnioy in the surface layer can inhibit the release of Ni.
6. Gentle orthodontic treatment: the current commercial orthodontic wire applications include austenitic stainless steel wire, cobalt chromium nickel wire, nickel chromium wire, Australian wire, gold wire and? Titanium alloy wire. The load displacement curves of these orthodontic wires under tensile test and three-point bending test conditions.
The Zui of nitinol unloading curve platform is the lowest and smoother, indicating that it provides the most lasting and mild corrective measures.
7. Good shock absorption performance: the greater the vibration of arch wire caused by chewing and night molars, the greater the damage to root and periodontal tissue. Through different attenuation test results, it is found that the vibration amplitude of stainless steel wire of arch wire is greater than that of super elastic nickel titanium wire, and the initial vibration amplitude of super elastic nickel titanium arch wire is only half of that of stainless steel wire, which has good vibration and damping characteristics. The protection of arch wire is very important for the health of teeth. Traditional arch wire, such as stainless steel wire, often increases the root absorption.
