Memory alloy, because it has the ability to recover more than a million times, so many people call it "living alloy". It is precisely because memory alloy is a "living alloy". Using its shape change at a certain temperature, we can design all kinds of automatic control devices, and its use is expanding.
Mechanical use
Memory alloys are widely used. For example, mechanical fastening pins and pipe joints, fire alarms, connectors and integrated circuit Brazing on electronic instruments and equipment, medical artificial heart valves, spinal correction rods, skull repair and plastic surgery, oral and dental orthopedics and jaw repair surgery. It will also play a magical role in communication satellites, color televisions, temperature controllers and toys. It will also become a new material in modern navigation, aviation, aerospace, transportation, light textile and other fronts. Memory alloy has been used in pipeline combination and automatic control. Casing made of memory alloy can replace welding. The method is to fully expand the pipe end by about 4% at low temperature. When it is assembled, it will be sleeved together. Once heated, The sleeve shrinks and returns to its original shape to form a tight joint. The hydraulic system of U.S. Navy aircraft uses 100000 such joints, and there has been no oil leakage or damage for many years. The damage of ships and submarine oil field pipelines can be repaired with memory alloy fittings, which is very convenient. In some parts with inconvenient construction, the pins are made of memory alloy and installed into the holes for heating, and their tail ends are automatically separated and curled to form single-sided assemblies.
Memory alloy is especially suitable for thermomechanical and constant temperature automatic control. It has been made into room temperature automatic opening and closing arm, which can open the ventilation window in the sunny day and close automatically when the room temperature drops at night. There are also many design schemes of memory alloy heat engine. They can work between two media with low temperature difference, which opens up a new way to use industrial cooling water, nuclear reactor waste heat, ocean temperature difference and solar energy. At present, the common problem is that the efficiency is not high, only 4% ~ 6%, which needs to be further improved.
Medical use
The application of memory alloy in medical treatment is also very attractive. For example, the bone plate used for bone connection can not only fix the two sections of broken bones, but also produce compressive force in the process of restoring the original shape, forcing the broken bones to join together. Orthodontic wires for dentistry, long clips for ligating cerebral aneurysms and vas deferens, and support plates for spinal straightening are all started by the action of body temperature after implantation in the human body. Thrombus filter is also a new product of memory alloy. After the straightened filter is implanted into the vein, it will gradually return to a mesh, preventing 95% of the clots from flowing to the heart and lungs.
Artificial heart is a kind of organ with more complex structure. The muscle fiber made of memory alloy and elastomer membrane ventricle can simulate the contraction of ventricle. Now pumping water has been successful.
As memory alloy is a kind of "living alloy", using its shape change at a certain temperature, all kinds of automatic control devices can be designed, and its application is expanding.
Earliest applicable
The earliest application of shape memory alloy is in pipe joints and fasteners. The shape memory alloy is used to process the casing whose inner diameter is 4% smaller than the outer diameter of the pipe to be connected, and then expand the diameter of the casing by about 8% under the temperature of liquid nitrogen. During assembly, take out the casing from liquid nitrogen and insert the pipe to be connected from both ends. When the temperature rises to normal temperature, the sleeve shrinks to form a tight seal. This kind of connection mode has close contact and can prevent leakage, which is far better than welding. It is especially suitable for dangerous occasions such as aviation, aerospace, nuclear industry and submarine oil pipeline.
Aerospace Technology Application
The most encouraging application of memory alloys is in aerospace technology. On July 20, 1969, the Apollo 11 lunar module landed on the moon, realizing the dream of mankind's first trip to the moon. After the astronauts landed on the moon, a hemispherical antenna with a diameter of several meters was placed on the moon to send and receive information to the earth. An antenna several meters large was installed in a small lunar module and sent into space. The antenna was made of memory alloy, which was just invented at that time. It is made of very thin memory alloy material according to the predetermined requirements under normal conditions, then reduce the temperature, press it into a ball, put it into the lunar module and take it to heaven. After being placed on the lunar surface, the temperature rises under the sunlight. When the transition temperature is reached, the antenna "remembers" its original appearance and becomes a huge hemispherical shape.
More uses
At present, shape memory effect and hyperelasticity have been widely used in various fields of medicine and life. Such as making thrombus filters, spinal orthopedic rods, bone plates, artificial joints, women's bras, artificial hearts and so on. It can also be widely used in various automatic adjustment and control devices. Shape memory films and filaments may become ideal materials for ultra micro manipulators and robots in the future. Especially its light weight, high strength and corrosion resistance make it popular in various fields.
