As early as the Qin Dynasty, there were memory metals such as Gou Jian, Qin Jianwang, and the Yue Dynasty.

In 1932, Schering-Plough of Sweden first observed the "memory" effect in gold-cadmium alloys, that is, when the shape of the alloy changed, once it heated to a certain jumping temperature, it could magically return to its original shape. This special-function alloy is called a shape memory alloy. The development of memory alloy has only been for more than 20 years, but because of its special role in various fields, it is attracting widespread attention in the world and is called "magic functional materials".

In 1963, Biller of the Naval Ordnance Research Institute found that in the temperature range above room temperature, the nickel-titanium alloy wire was fired into a spring, then stretched or cast into a square or triangle in cold water, and then placed above 40 degrees Celsius Hot water. The alloy wire returns to its original spring shape. Later, it was discovered that other alloys also had similar functions. These alloys are called shape memory alloys. Each shape memory alloy composed of a certain weight ratio of an element has a transition temperature. Above this temperature, the alloy is processed into a certain shape, then cooled to below the transition temperature, and then its shape is artificially changed, and then heated. Above the transition temperature. E transition temperature, the alloy will automatically return to the transition temperature above the original processed shape.

In 1969, the shape memory effect of nickel-titanium alloy was first applied in industry. Using a unique pipe joint device. In order to connect two metal pipes to be docked, a shape memory alloy with a transition temperature lower than the use temperature is used to make a short pipe with an inner diameter slightly smaller than the outer diameter of the butt (joint) pipe under the following conditions: the transition temperature is higher than that of the metal pipe to be docked Transition temperature. Then the inner diameter of the pipe increases slightly below the transition temperature, and then the connecting pipe is placed in the transition temperature of the joint. The joint automatically shrinks and fastens the connection tube to form a firm, tight connection. A certain type of jet fighter hydraulic system in the United States uses nickel-titanium alloy joints. There has never been an oil spill, shedding, or breakage.

7On July 20, 1969, American astronauts on the Apollo 11 lunar module left human footprints on the moon for the first time and transmitted information between the moon and the Earth through a hemispherical antenna with a diameter of several meters. How did this huge antenna reach the moon? It is made of a shape memory alloy material, consisting of the required temperature above its transition temperature, then lowering the temperature to press it into a ball, and then putting it into the lunar capsule Hit it into the sky. When the antenna is placed on the moon, it "remembers" its true appearance, and when it reaches the alloy's transition temperature in the sun, it becomes a giant hemisphere.

The scientists added other elements to the nickel-titanium alloy and further developed new nickel-titanium shape memory alloys, such as Qin nickel alloy, Tianning iron, Tianning chromium and so on. In addition, there are other types of shape memory alloys, such as copper-nickel alloys, copper-aluminum alloys, copper-zinc alloys, and iron. Alloys (iron manganese silicon, iron palladium) and the like.

Shape memory alloys also have broad application prospects in the fields of biological engineering, medicine, energy and automation.