In 1932, Sweden was first observed in human Orland in gold-cadmium alloy "memory" effects, namely alloy shape is changed, when heated to a certain degree of transition temperature, it can magically changed back to its original shape, people with the special features of alloys known as shape memory alloys. Memory alloys developed so far, but more than 20 years, but because of its special effects applications in various fields, are widespread attention, known as "magic material."In 1963, the United States Institute of Naval Ordnance Buehler stumbled upon the nickel-titanium alloys with shape memory effect, this discovery a sensation in the international community as a whole, and was soon applied to cutting-edge technology ...

In 1969, the nickel-titanium alloys--"shape memory effect" was first applied in industry. People using a different device for pipe joints. To will two root need docking of metal tube connection, selection change temperature below using temperature of a species shape memory alloy, in above its change temperature of conditions Xia, made diameter than stay docking pipe od slightly small is of short tube (for joint with), then in below its change temperature Xia will its diameter slightly spread to the joint of change temperature Shi, joint on automatically contraction and buckle tight was received pipeline, formed firm close of connection. United States at some jet fighter of the hydraulic system uses a nickel-alloy joints Chennai, oil leakage, loss or damage accidents has never occurred.

On July 20, 1969, the United States astronaut on board the "Apollo", 11th lunar module on the Moon for the first time leave human footprints, and a half-spherical antenna several meters in diameter the Moon between the Earth and the information. How did this monstrous antennas was brought to the Moon? using a shape memory alloy, in its transition temperature above a predetermined requirements, and then lower the temperature and press it into a ball, into the lunar module with up to heaven. On the Moon, in the Sun, reaching its transition temperature, antenna "remember" their original appearance, into a gigantic dome.

A memory alloy is a martensitic alloy with a rule and a volume of less than 0.5%.This kind of alloy can produce deformation under the force of external force, when the outside force is removed, at certain temperature condition, can restore original shape.Because it has more than a million restorative functions, it is called "memory alloy".It is unlikely, of course, that the human brain will remember, or rather, the "alloy of memory shape".In addition, the memory alloy also has no magnetic, the advantages of wear-resisting corrosion resistance, non-toxic, therefore,they are widely used as making thermostat temperature control circuit, the aircraft aerial refueling interface and so on.Scientists have now discovered dozens of alloys of different memory functions, such as titanium-nickel alloys, gold-cadmium alloys, copper-zinc alloys, etc.

temperature in the Shape of the plastic deformation and fixed into another kind of shapes, by heating to the above a certain critical temperature and can be back to the initial Shape of alloy. Shape Memory alloy is able to remember its original Shape of the function is called Shape Memory Effect, Shape Memory Effect, SME). Shape Memory alloy as a special kind of new functional materials, is a concentration of perception and drive in the integration of intelligent materials, because of its unique function, can make small and exquisite, highly automated, reliable performance of components and high-profile, and have gained a wide range of applications.

The development history and present situation of shape memory alloy can be traced back to the 1930s.In 1938, Greningerh and mooro-than in the United States discovered the martensite's thermoelastic transition in the cu-zn alloy.Subsequently, the former Soviet union Kurdiumo, studied the phenomenon.In 1951, Chang and Read looked at the martensitic interface with the light microscope in the au-47.5 at zero o Cd alloy and moved with the temperature.This is the first report to observe the effect of metal shape memory.A few years later, Burkhart observed the same phenomenon In an in-ti alloy.At the time, however, the findings of these phenomena were seen only as a special phenomenon of individual materials that failed to attract enough interest and attention.Straight to 1963, such as the United States naval weapons LABS Buehler and others found that atomic ratio of Ti Ni alloy has excellent shape memory function, and successfully developed the practical shape memory alloys "Ni} - nol", has attracted widespread interest, the study of shape memory alloy has entered a new stage.

The two main types of shape-memory alloys are copper-aluminium-nickel, and nickel-titanium (NiTi) alloys but SMAs can also be created by alloying zinc, copper, gold and iron. Although iron-based and copper-based SMAs, such as Fe-Mn-Si, Cu-Zn-Al and Cu-Al-Ni, are commercially available and cheaper than NiTi, NiTi based SMAs are preferable for most applications due to their stability, practicability[1][2][3] and superior thermo-mechanic performance.[4] SMAs can exist in two different phases, with three different crystal structures (i.e. twinned martensite, detwinned martensite and austenite) and six possible transformations.[5][6]

 

NiTi alloys change from austenite to martensite upon cooling; Mf is the temperature at which the transition to martensite completes upon cooling. Accordingly, during heating As and Af are the temperatures at which the transformation from martensite to austenite starts and finishes. Repeated use of the shape-memory effect may lead to a shift of the characteristic transformation temperatures (this effect is known as functional fatigue, as it is closely related with a change of microstructural and functional properties of the material).[7] The maximum temperature at which SMAs can no longer be stress induced is called Md, where the SMAs are permanently deformed.[8]

 

The transition from the martensite phase to the austenite phase is only dependent on temperature and stress, not time, as most phase changes are, as there is no diffusion involved. Similarly, the austenite structure receives its name from steel alloys of a similar structure. It is the reversible diffusionless transition between these two phases that results in special properties. While martensite can be formed from austenite by rapidly cooling carbon-steel, this process is not reversible, so steel does not have shape-memory properties.

 

Shape Memory alloy ((Shape Memory Al long, SMA) refers to a certain initial alloy under the low temperature in the Shape of the plastic deformation and fixed into another kind of shapes, by heating to the above a certain critical temperature and can be back to the initial Shape of alloy. Shape Memory alloy is able to remember its original Shape of the function is called Shape Memory Effect, Shape Memory Effect, SME). Shape Memory alloy as a special kind of new functional materials, is a concentration of perception and drive in the integration of intelligent materials, because of its unique function, can make small and exquisite, highly automated, reliable performance of components and high-profile, and have gained a wide range of applications.

 

The discovery of shape memory effects in metals dates back to the 1930s.In 1938, the American Greningerh and Moora - than found martensite's thermal elastic transformation in Cu - Zn alloy.Subsequently, the former Soviet union Kurdiumo, studied the phenomenon.In 1951, Chang and Read observed that the martensitic interface was moved with the temperature of an optical microscope in the au-47.5 at 0 o Cd alloy.This is the first report to observe the effect of metal shape memory.A few years later, Burkhart observed the same phenomenon In in-ti alloys.At the time, however, the findings of these phenomena were seen only as a special phenomenon of individual materials that did not attract enough interest and attention.Straight to 1963, such as the United States naval weapons LABS Buehler and others found that atomic ratio of Ti Ni alloy has excellent shape memory function, and successfully developed the practical shape memory alloys "Ni} - nol", has attracted widespread interest, the study of shape memory alloy has entered a new stage.

 

Shape memory alloy (shape memory alloy) has been widely used in clinical medical field, such as artificial bone, bone injury fixed pressurizer, dental adjust device, various cavity mounts, embolism, cardiac repair, thrombus filters, interventional godet and surgical sutures, etc., memory alloy is plays an irreplaceable role in the modern medical.Memory alloys are also associated with our daily lives.