What is memory alloy 1870s , the world there is a materials science with alloy " memory" shape function . Memory is a rather special alloy metal bars , it can easily be bent , we put it in the container of hot water aquarium , metal strips rushed forward ; put it into cold water , the metal strip is restored the status quo. Container of cold water in the aquarium , the stretch of a spring , when the spring into the hot water , springs and automatically folded up . Cold water in the spring to restore its original state , while in hot water , it will shrink , spring can be an unlimited number of stretching and shrinking , shrinking again opened. The memory consists of an intelligent made of metal , the microstructure of which has two relatively stable at high temperatures of the alloy can be turned into any shape you want, the alloy at lower temperatures can be stretched , but if it is reheated , it will remember its original shape , and change back. This material is called memory metal (memory metal). It is mainly a nickel titanium material. For example , a helical superalloy, after high temperature annealing , which is in the shape of a spiral state. At room temperature , that is forced to use a lot of effort to straighten it , but as long as it is heated to a certain " abnormal temperature ," which seemed to root alloy remembered something, now restored to its original helical shape . How is this going ? Did alloy also has a kind of human memory ? Original not the case ! It's just the use of certain alloys law changes the crystal structure in the solid state with temperature only. For example , a nickel - titanium alloy 40oC 40oC above and below the crystal structure is different, but the temperature change in the vertical 40oC , will be contracted or expanded metal , such that its shape is changed . Here , 40oC is a nickel - titanium shape memory alloy "abnormal temperature ." Various alloys have their own perverted temperature. Abnormal high temperature superalloys above that . At high temperatures it is spirally formed in a stable state . At room temperature when it forcibly straightened, it is in an unstable state , sunrui Titanium alloy valve so long as it is heated to a temperature of metamorphosis , it is immediately restored to the spiral shape of the original is in a stable state . Classification and application of shape memory alloy can be divided into three types: ( 1 ) one-way shape memory alloy memory effect deformation at low temperature before heating the deformed shape recoverability , which exists only in the heating process of shape memory One way is called memory effect . ( 2 ) Two-way memory effect of certain alloys with shape recovery temperature heating , cooling can restore the shape of the low temperature phase , called the two-way memory effect. ( 3 ) recovery throughout the high-temperature phase shape memory effect heating , cooling into the same shape and the shape of the opposite orientation of the low-temperature phase , called the whole memory effect. Three kinds of memory effect is shown below. Has been successfully developed TiNi shape memory alloy based shape memory alloys, copper-based shape memory alloys , iron-based shape memory alloys. The earliest reports of the shape memory effect and Read by Chang et al made in 1952 . They observed Au-Cd alloy reversible phase transformation . Later in the Cu-Zn alloys also found the same phenomenon, but did not attract widespread attention . Until 1962 , Buehler and his collaborators observed with macroscopic shape memory effects such as changes in the atomic ratio of TiNi alloy , it attracted the attention of materials science and industry . By the early 1970s , CuZn, CuZnAl, CuAlNi also found in other alloys with shape memory effect martensitic transformation related . For decades, research on shape memory alloy has gradually become an important issue of international conferences and phase change materials conferences , and has held a number of symposia , and constantly enrich and improve the martensitic aerospace investment castings transformation theory . In theory deepening , while the application of shape memory alloys have also made considerable progress, its scope of application involves many areas of mechanical , electronic, chemical , aerospace , energy and medical. Specific applications of shape memory alloys below. Industrial applications: ( 1 ) the use of one-way shape memory effect of a one-way shape recovery . Such as pipe fittings, antenna , rings and so on. ( 2 ) extrinsic two-way memory recovery. Namely the use of one-way shape memory effect and lifting to do with the temperature outside help repeated actions, such as heat-sensitive components, robots, terminals , etc. ( 3 ) intrinsic two-way memory recovery. Namely the use of two-way memory effect with temperature elevating do repeated actions, such as heat engines , thermal components. But such applications faster memory decay , poor reliability , not commonly used. ( 4 ) ultra- flexible application . Such as springs , terminal, eyeglass frames and so on. Medical Applications : biocompatibility TiNi alloy good use of its shape memory effect and superelasticity medical instances considerable . If the filter thrombosis , spinal orthopedic rods, tooth orthopedic wire, cerebral aneurysm clips, plates , intramedullary nail , artificial joints, contraceptive devices , cardiac repair components, artificial kidneys using a micro- pumps. Tech applications Outlook: The 20th century was the era of mechanical and electrical science . Sensing - IC - driving is the most typical mechanical and electronic control systems, but the complexity and huge . Shape memory materials both sensing and driven dual function , the control system can achieve miniaturization and intelligent robots such as holograms , ultra- millimeter micro robots. The 21st century will be the era of e- learning materials . Action shape memory alloy robot addition to temperature conditions without any environmental impact is expected in high-tech fields reactors, accelerators , space laboratories flourish. Memory alloy spoke alloys, of course, talk about the most interesting alloys - memory alloy . Metal has a memory , an accidental discovery : the early 1960s , a research team from the U.S. Navy led to some of the warehouse nitinol wire experiments , they found that these alloy wire winding , very easy to use , so he took these alloy wire a root straightened. During the test , a strange phenomenon , they found that when the temperature rose to a certain value , which has been straightened nitinol wire suddenly restored to its original state bent , they are good at observing the heart, and repeated done several tests , the results have confirmed these filaments do ? "memory ." The discovery of Naval Research , and aroused great interest in the scientific community , a large number of scientists have conducted in-depth research . Found that zinc alloy , copper-aluminum -nickel alloy , copper-molybdenum -nickel alloy , zinc alloy, copper and gold also have this strange ability . It may be in a certain range , according to the need to change the shape of these alloys to a particular temperature, they automatically return to their original shape , and this " change - recovery " may be repeated several times , regardless of how changes they always remember the shape of his own time , to this temperature , it is no less to the prototype reproduction. It is called the shape memory effect of this phenomenon , the metal having such a shape memory effect is called a shape memory alloy , referred to as memory alloy . Why are these alloys can have such a shape memory effect ? How they remember their original shape ? With the general theory of metallic bonds , free electron theory is difficult to explain the effect of this memory alloy . Memory alloy under certain temperature conditions can be restored to original shape for sports extranuclear - movement with temperature changes , provides an excellent example. It is due to the formation of the alloy at high temperature of the liquid metal melt each other , since the structure of the liquid metal element rejection , resulting in the structure of another metal element and the structure of each element of this element uniform solidification , its microstructure is ordered different types of structure element proportional to the electromagnetic force is the main object of the alloy constituting the cohesion . The electromagnetic force is formed by the valence and electronic operation of the electronic operating rate changes with temperature , so the electromagnetic force ( size, direction , action point ) is also inside the object temperature conditions. The resulting internal forces of metal objects with temperature changes , but these changes within a small range of temperature difference is not obvious , only performance only in the larger temperature changes ( several hundred degrees C) . Force in the general metal , can be plastically deformed as a wire is bent , the bending portion , the electromagnetic force by the external disturbance , resulting in operation of an electromagnetic plane and force electrons to the valence micro adjustment , a plastic deformation completed . Due to the different types of memory alloy structural element uniform blending with each other , despite the different size of the structure element tall, electromagnetic force , but each has its own price and speed up the operation , under certain temperature conditions adjacent peace and quiet . After the external force , the electromagnetic force of the external disturbance , and the valence electrons run to the plane of trace angle adjustment , the object is plastically deformed , in this plastic deformation , the price and the adjustment operation of the electronic part is not stretched . When the rate of change of temperature change with current prices and electrons when the temperature returns to the refreshing phase of development (transition temperature ) conditions , and does not stretch the valence electrons immediately run back to the time rate of change along the electromagnetic force , the adjacent structural element of price and running are also adjusted accordingly , the entire stretch back to the original state , so the whole object also return to the original state. This is the memory of the process memory alloy . In fact, the memory metal has long been found : a straight wire bent to a right angle (90 °), a release , it is necessary to restore it to form an angle larger than 90 ° . Put a bent wire straightening , it must fold to over 180 ° and then released, so that it can just return to the straight state, which is the Chinese idiom spoken overkill. There is a better memory alloy spring , ( talking about here is a steel spring , steel is an iron -carbon alloy ) spring firmly remember their shape , force a withdrawal , immediately return to their original appearance, only a wide temperature memory spring , so there is not a specific memory alloys transition temperature, which has some special functions . With the memory alloy deformation function at a particular temperature , the temperature can produce a variety of devices, the temperature control circuit can be produced , thermostatic door , temperature of the pipe connection . People have made use of automatic memory alloy fire hydrant - fire temperature, memory alloy deformation, so that the valve opens, water spray fire. Making a connection to connect the mechanical parts , pipes , air refueling aircraft interface is the use of a shape memory alloy - two oil pipes tacking , the use of electric heating temperature change , the interface memory alloy deformation, so that the interface tight dripping ( oil ) does not leak . Making the area of several hundred square meters of space station antenna from Fair - first made large parabolic antennas or planar , folded into a ball on the ground, with the spacecraft to the space , the temperature changes , since the development of a large area and the original shape. Memory alloys have been to dozens of current development in the aerospace, military, industrial, agricultural , medical and other fields have a purpose , and the development trend is very impressive, it is grand plans for the benefit of mankind.
Shape memory alloys have been found so far a dozen memory alloy system. Include Au-Cd, Ag-Cd, Cu-Zn, Cu-Zn-Al, Cu-Zn-Sn, Cu-Zn-Si, Cu-Sn, Cu-Zn-Ga, In-Ti, Au-Cu-Zn , NiAl, Fe-Pt, Ti-Ni, Ti-Ni-Pd, Ti-Nb, U-Nb and Fe-Mn-Si , etc.
Application memory alloy application memory alloy is widely used. For example, the fastening pin machinery, fittings, fire alarm on electronic equipment , connectors , integrated circuits, soldering , artificial heart valves for medical , chiropractic stick, skull repair surgery, orthopedic and oral teeth mandible repair surgery. It will also play a magical performance in a communications satellite , color TV , temperature controllers and toys , etc., will also be new material on all fronts , modern maritime, aviation , aerospace , transportation , textile and so on.
Memory alloy pipe has been used in combination with automatic control , the sleeve may be made of shape memory alloy instead of welding , is in the low temperature expansion of the tube to approximately 4% of the full , a socket assembly with a heated , shrinkage of the sleeve restore the prototype , form a tight engagement . U.S. Navy aircraft hydraulic system uses a 100,000 such joints, oil spills and damage over the years never happened . Ship and submarine oil pipeline damage , sunrui titanium alloy coils repair it with a shape memory alloy fittings, very convenient. In some parts of the inconvenience of construction , the pin made of shape memory alloy , into the hole is heated to separate the trailing end automatically curl to form single assembly .
Memory alloy is particularly suitable for thermo-mechanical and automatic temperature control , automatic opening and closing has made room arm can open the windows are in the sunshine during the day , automatically turns off when the night temperature drops. Memory alloy heat engine designs are also a lot that they can be in with a low temperature difference between the two media work , so as to take advantage of industrial cooling water , nuclear reactor heat, ocean thermal and solar power opened up new avenues . Now the problem is widespread efficiency is not high, only 4 % to 6% , to be further improved .
Memory alloys in medical applications is also very compelling. E.g., the bone with the bone plate , not only can two fixing broken bones , and the recovery of the original shape of the compression force is generated , forcing the broken bones are joined together . After straightening teeth using dental wire , long clip ligation of cerebral aneurysms and vas deferens , with the support plate straightening the spine , are implanted in the human body temperature by the action starts, thrombus filter is also a new product memory alloy . After being straightened filter implanted vein , will be gradually restored into a network , thereby preventing clot 95% flow to the heart and lungs.
Artificial heart is a more complex structure of the organ , muscle fibers of the elastic memory alloy thin film made of ventricular cooperate to mimic ventricular contraction . Now water is pumped been successful.
Since memory alloy is a " life has alloy " , use it at a certain temperature changes shape , you can design all kinds of self-control devices , its use is expanding . The first application of shape memory alloy pipe fittings in and fasteners . A shape memory alloy is processed into an outer diameter smaller than the internal diameter of the pipe to be connected to the casing 4% , at liquid nitrogen temperature and then expanding the sleeve diameter of about 8% , this will be removed from the cannula assembly when the liquid nitrogen , the desire inserted from both ends of the tube connection . When the temperature was raised to room temperature , i.e., the sleeve forming a holding seal shrinkage . This connection can be in close contact with anti-leakage , far better than welding , especially suitable for aviation, aerospace , nuclear industry and submarine pipelines and other dangerous situations. The most promising application memory alloys in aerospace technology . July 20, 1969 , "Apollo" 11 lunar module landed on the moon , the first human landing on the moon to achieve the dream of traveling . After the astronauts landing on the moon , on the moon a few meters in diameter placed a large hemispherical antenna for transmitting and receiving information to Earth . A few meters from a large antenna mounted on the tiny lunar module sent into space inside . Antenna that was just invented near memory alloy used. Under normal circumstances, the first predetermined requirements of good memory alloy material with a very thin , then lower the temperature to press it into a ball , bring the day to go into the lunar module . Into the lunar surface after the temperature rise in the sunlight , when it reaches the transition temperature , antennas and " mind" from their original appearance , becomes a huge domed . At present, the shape memory effect and superelasticity has been widely used in various fields of medicine and life . Thrombus filter manufacturing , spinal orthopedic rods, plates , artificial joints, women bra , artificial heart and so on. Can also be widely used in a variety of automatic regulation and control devices. Shape memory films and filaments may be the ideal material for future ultra- miniature robots and robots. Especially its light weight, high strength and corrosion resistance makes it highly popular in various fields .
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