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Shape memory alloy is an alloy that can automatically restore its plastic deformation to its original shape at a certain temperature.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.Nitinol alloy composition amolst incluing nickel and titanium.
The expansion rate is above 20%. The fatigue life is up to 107 times, the damping characteristic is 10 times higher than that of ordinary springs, and its corrosion resistance is excellent.It is 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.
Nitinol alloy uses in many field The production can be applied to glasses legs, women's bras, mobile phone antennas,high-quality memory in the fields of women's birth control rings, dental arch wires, instruments and meters alloy wire.In 1963, the U.S. naval same Ordnance Research Laboratory needed some nickel-titanium alloy wires in an experiment, and the alloy wires they brought back were all crooked. For ease of use, these twisted filaments were straightened one by one and used.
In the follow-up test, a strange phenomenon appeared: when the temperature rose to a certain value, these alloy wires that had been stretched straight suddenly and magically quickly recovered to their original crooked shape, and the same as the original The shape is not bad at all. After repeated experiments, the results are exactly the same every time. As long as the straightened alloy wire reaches a certain temperature, it will immediately return to its original bendy appearance.
It's as if people changed their shape when they were "frozen" and unconscious. When the temperature rises to a certain value, they suddenly "wake up" and "remember" their original appearance again, so they just Desperate to restore his "true colors."
Nitinol alloy properties is very outstanding .The crystal structure of nickel-titanium alloy above 40oC and below 40oC is different, but when the temperature changes around 40oC, the alloy will shrink or expand, causing its morphology to change.here, 40oC is the "transformation temperature" of the nickel-titanium memory alloy. Various alloys have their own transformation temperature.
Memory alloy has been used for pipeline bonding and automatic control. The sleeve made of memory alloy can replace welding. The method is to expand the inner end of the pipe by about 4% at low temperature and sleeve it together during assembly. Once heated, the sleeve shrinks. Restore the original shape and form a tight bond.
The hydraulic system of the U.S. Navy aircraft uses 100,000 of these joints, and there has been no oil leakage or damage for many years. Damaged ships and subsea oilfield pipelines can be repaired with memory alloy fittings, which is very convenient. In some places where construction is inconvenient, the pins are made of memory alloy and heated in the holes. The ends of the pins are automatically crimped to form a single-sided assembly.
The memory alloy is particularly suitable for thermomechanical and automatic constant temperature control. It has been made into a room temperature automatic opening and closing arm, which can open the ventilation window during the day when the sun is shining, and automatically close when the room temperature drops at night.
There are also many design schemes for memory alloy heat engines. They can work between two media with a low temperature difference, thus opening up new ways for the use of industrial cooling water, nuclear reactor waste heat, ocean temperature difference and solar energy. The common problem now is that the efficiency is not high, only 4% to 6%, which needs to be further improved.the medical application of memory alloy is also very attractive.
For example, a bone plate used for bone fixation can not only fix two broken bones, but also generate compressive force during the process of restoring the original shape to force the broken bones to join together. The orthodontic wire for dentistry, the long clip for ligating cerebral aneurysm and vas deferens, the support plate for spine straightening, etc., are all activated by body temperature after being implanted in the human body. Thrombus filter is also a new product of memory alloy . After the straightened filter is implanted in the vein, it will gradually return to a mesh shape, thereby preventing 95% of the clot from flowing to the heart and lungs.
Artificial heart is an organ with more complex structure. Muscle fibers made of memory alloy cooperate with the ventricle of the elastomer membrane, which can imitate the contraction movement of the ventricle. Now pumping water has been successful.
Because memory alloy is a "live alloy", by using its shape change at a certain temperature, it is possible to design all kinds of automatic control devices, and its use is expanding.