Memory alloys are widely used. For example, mechanical fastening pins, pipe joints, fire alarms, sockets and brazing of integrated circuits on electronic instruments and equipment, artificial heart valves, vertebral correction sticks, cranioplasty, oral and dental orthopedics, and jaw repair operations. It will also play a magical role in communication satellites, color TV sets, temperature controllers and toys. It will also become a new material memory alloy for modern navigation, aviation, aerospace, transportation, textile and other battlefields. It has been used in pipeline bonding and automation control. Casing made of memory alloy can replace welding. The method is to complete the pipe end at low temperature. Expansion of about 4%, assembly socket together, once heated, casing shrinkage restored to its original shape, forming a tight connection. The hydraulic system of U.S. Navy aircraft uses 100,000 of these connectors, and for many years there has been no oil leakage or damage. It is very convenient to repair damaged ship and submarine oil field pipelines with memory alloy fittings. In some parts where construction is inconvenient, memory alloy pins are made and heated into holes. The tail ends of pins are automatically separated and curled to form one-sided assemblies.
Memory alloy is especially suitable for thermo-mechanical and constant temperature automatic control. It has been made into room temperature automatic opening and closing arms. It can open ventilation windows in sunshine day and shut down automatically when room temperature drops at night. There are many design schemes for memory alloy heat engines, which can work between two media with low temperature difference, thus opening up a new way to utilize industrial cooling water, waste heat of nuclear reactor, ocean temperature difference and solar energy. At present, the common problem is that the efficiency is not high, only 4%-6%, which needs further improvement.
Medical applications:
Memory alloys have also attracted considerable attention in medical applications. For example, the plate used for bone grafting can not only fix two broken bones, but also produce compressive force in the process of restoring the
original shape, forcing the broken bones to join together. Dental orthodontic wires, long clips for ligating cerebral aneurysms and vas deferens, and supporting plates for spinal straightening are all activated by body temperature after
implantation. Thrombosis filters are also a new memory alloy product. After the straightened filter is implanted into the vein, it gradually restores to a net shape, thus 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 fibers made of memory alloy can imitate the contraction of ventricle by matching with the elastomeric membrane ventricle. Now pumping water has been successful.
Because memory alloy is a kind of "living alloy", various kinds of automatic control devices can be designed by using its shape change at a certain temperature, and its use is expanding.
The earliest application:
The earliest applications of shape memory alloys were in pipe joints and fasteners. Shape memory alloy (SMA) is used to manufacture a sleeve with an inner diameter of 4% smaller than the outer diameter of the connecting pipe. Then the sleeve is expanded by about 8% at liquid nitrogen temperature. When assembled, the sleeve is removed from liquid nitrogen and the connecting pipe is inserted from both ends. When the temperature rises to normal temperature, the casing shrinks to form a tight seal. This kind of connection is tightly contacted and leakproof, which is much better than welding. It is especially suitable for dangerous occasions such as aviation, aerospace, nuclear industry and submarine oil pipeline.
Applications of Space Technology:
The most encouraging application of memory alloys is in space technology. On July 20, 1969, Apollo 11 lunar module landed on the moon, realizing the dream of the first human trip to the moon. After the astronauts landed on the moon, a hemispherical antenna several meters in diameter was placed on the moon to send and receive information to the earth. Several meters of antenna was put into space in a small lunar module. The antenna was made of a memory alloy that had just been invented. The very thin memory alloy material is first prepared according to the scheduled requirements under normal conditions, and then lowered the temperature to press it into a ball, which is loaded into the lunar module and carried to the sky. After being placed on the moon, the temperature rises under the sunlight. When the temperature reaches the transition temperature, the antenna "remembers" its true appearance and becomes a huge hemisphere.
More applications:
At present, shape memory effect and hyperelasticity have been widely used in various fields of medicine and life. Such as making thrombus filters, spine rods, bone plates, artificial joints, women's bras, artificial hearts and so on. It
can also be widely used in various automatic regulation and control devices. Shape memory films and filaments may become ideal materials for future ultra-micro manipulators and robots. Especially its light weight, high strength and
corrosion resistance make it popular in various fields.
A nickel-titanium alloy with the shape of "ICE" is prepared in advance. After its shape is pulled out carelessly, it can be restored to its original shape as long as it is soaked in hot water.
The shape of the nickel-titanium alloy mixed in half can be maintained permanently after 10 minutes of slow forging at high temperature of Sibaidu Celsius (at this time, it is called the high temperature phase Austenite form).
The main reason is that each metal atom will have enough time to fill every void during the slow heating process of crystallization. At this time, its arrangement and combination are the most compact. The commercial name of such alloy solid is memory alloy. If the shape memory alloy is deformed by any external factors (the configuration that can be deformed arbitrarily is called the martensitic state of Masada loose iron), that is to say, the crystalline voids will be formed, and the voids will be filled when the temperature of transformation is slightly higher than that of transformation temperature, that is to say, the process of restoring the original state is called shape memory.
