Shape memory alloys are widely used in many fields such as aerospace, machinery and electronics, biomedical, bridge construction, automotive industry and daily life because of their many excellent properties.
(1) Applications in the aerospace industry[5]
Shape memory alloys have been applied to aviation and space devices. For example, it is used in the hydraulic system of military aircraft for low-temperature fit connectors, and Europe and the United States are developing shape memory alloy materials used in the intelligent horizontal rotor of helicopters. As the helicopter high vibration and high noise use is limited, the source of its noise and vibration is mainly blade vortex interference, as well as the blade profile of the small deviation. This requires a device to balance the blade pitch so that each blade can rotate precisely in the same plane. A trajectory controller for the blades has been developed, which uses a small double-tube shape memory alloy actuator to control the position of the winglets on the blade edge trajectory to minimize their vibration [6].
It can also be used to create a lunar antenna to explore the mysteries of the universe, people use shape memory alloy to make a good antenna in a high-temperature environment, and then at a low temperature to compress it into a small iron ball, so that its volume shrinks to one-thousandth of its original size, so it is easy to transport to the moon, and the sun's strong radiation makes it restore its original shape, in accordance with the needs of the Earth back to the valuable information about the universe.
In addition, a shape memory release device with an openable container is used in the satellite to protect the sensitive germanium detector from contamination during assembly and launch.
(2) Applications in Mechatronics[7]
Shape memory alloys were used in the United States to make cryogenic mating connectors on the F-14 Combat in 1970, followed by millions of applications for more than one connecting piece[5]. Shape memory alloys are used as cryogenic mating connections in hydraulic systems in airplanes and in smaller petroleum, petrochemical, and electrical industrial products. Another type of connectors is in the shape of welded mesh wires, which are used to create safety joints in the wire braid layer of the conductor. This kind of connector has been used for sealing devices, electrical connection devices, electronic engineering mechanical devices, and can work reliably at -65 ~ 300 ℃. Sealed system devices have been prescribed for use as electrical parts connections in harsh environments [6].
Shape memory alloys are made into a spring that opens and closes the shutter to protect fog lights from flying debris. Used in the manufacture of precision instruments or precision lathes, once deformed due to vibration, collision, etc., it only needs to be heated to troubleshoot the problem. In the mechanical manufacturing process, a variety of stamping and mechanical operations are often required to transfer parts from one machine to another, and now the use of shape memory alloys to develop a replacement for manual or hydraulic fixtures, this device is called the drive cylinder, which has a high degree of efficiency and flexibility, clamping force and other characteristics.
(3) biomedical applications [8]
TiNi shape memory alloy used in the medical field, in addition to the use of its shape memory effect or super-elasticity, it should also meet the requirements of chemistry and biology, that is, good biocompatibility. TiNi can be formed with the organisms of the formation of a stable passivation film. At present, the main applications of TiNi alloy in medicine are:
(a) orthodontic wire with superelastic TiNi alloy wire and stainless steel wire made of orthodontic wire, which is the most suitable with superelastic TiNi alloy wire. Usually orthodontic stainless steel wire CoCr alloy wire, but these materials have a high modulus of elasticity, the disadvantage of small elastic strain. In order to give the appropriate corrective force, it should be processed into an arch before orthodontic, and the ligation fixation requires skill. If TiNi alloy is used as dental orthodontic wires, even if the strain is as high as 10%, it will not produce plastic deformation, and the stress-induced martensite phase transition (stress-induced martensite) makes the elastic modulus show non-linear characteristics, that is, the strain increases when the corrective force fluctuation is very small. This material is not only easy to operate, good efficacy, but also reduce patient discomfort.
(b) scoliosis orthopedic various scoliosis (congenital, habitual, neurological, rickets, idiopathic, etc.) disease, not only physical and mental serious damage, but also the internal organs are compressed, so it is necessary to perform surgical orthopedics. At present, this kind of surgery adopts stainless steel Halton rod orthopedic, when placing the orthopedic rod in the surgery, the corrective force on the spine after fixation is required to be kept under 30~40kg, but if the force is too big, the orthopedic rod will be destroyed, as a result of which not only the spine, but also the nerves are in danger of being damaged. Meanwhile, the corrective force will change with time after the orthopedic rods are placed, and when the corrective force drops to about 30% of the initial force, it is necessary to adjust the corrective force again surgically, which causes great pain to the patients both mentally and physically. With the Harrington bar made of shape memory alloy, only one placement of the bar is required for fixation. If there is a change in the corrective force of the rod, sufficient corrective force can be restored by heating the shape memory alloy outside the body and raising the temperature to about 5°C higher than the body temperature.
In addition, TiNi shape memory alloy is used in surgery to make a variety of bone connectors, vascular clips, coagulation filters and vasodilator components. Also widely used in dentistry, orthopedics, cardiovascular, thoracic surgery, hepatobiliary, urology, gynecology, etc. With the development of shape memory, medical applications will be more extensive.
(4) Daily life applications[5]
(a) Anti-scalding valves In home life, developed shape memory valves can be used to prevent accidental scalding of hot water in sinks, tubs, and bathrooms; these valves can also be used in hotels and other suitable places. If the temperature of the water coming out of the faucet reaches a temperature at which scalding is possible (about 48°C), the shape memory alloy actuates the valve to close, and the valve does not reopen until the water temperature has dropped to a safe temperature.
(b) Eyeglass Frames Fitting TiNi alloys to the nose and ear portions of eyeglass frames provides comfort and resists abrasion, and the flexibility of TiNi alloys has led to their widespread use in changing the world of eyewear fashion. With superelastic TiNi alloy wires used for eyeglass frames, the shape memory alloy wires are able to grip the lenses with a constant force of superelasticity, even when the lenses expand thermally. These super-elastic alloys create eyeglass frames with a large deformation capacity, which is not possible with ordinary eyeglass frames.
(c) Cellular Phone Antennas and Fire Inspection Valves The use of superelastic TiNi wires for cellular phone antennas is another application of shape memory alloys. In the past, stainless steel antennas were used and often had damage problems due to bending. The use of TiNi shape memory alloy wires for cellular telephone antennas is popular because of their high resistance to damage. Therefore, it is often used to make cellular telephone antennas and fire inspection valves. In a fire, the valve closes automatically when the local area heats up, preventing the entry of dangerous gases. The advantage of this special structural design is that it has the operation of the check valve, and then reset to a safe state; this fire check valve in the semiconductor manufacturing industry has been used in the semiconductor manufacturing diffusion process using toxic gases; this fire check valve can also be applied in chemical and petroleum plants.
(5) other applications
In the field of engineering and construction with TiNi shape memory alloys as soundproofing materials and detection of earthquake damage control potential has been shown. Applications in bridges and buildings have been tested, so the use as a soundproofing material and detection of damage control has become a new field of application.
With the emergence and development and utilization of thin film shape memory alloy materials, shape memory alloys have been highly valued in smart material systems, and the prospects for their application are even broader.