The origin of shape memory alloys
志联
2025-04-18
In 1932, the "memory" effect was first observed by Swede "Olander" in a gold-cadmium alloy. This effect means that after the alloy's shape is changed, it magically returns to its original shape once heated to a certain transition temperature. Alloys with this special function are called shape memory alloys. Shape memory alloys have only been developed for over 20 years, but due to their highly effective applications in various fields, they have attracted worldwide attention and are hailed as "magical functional materials."
Memory metals existed as early as the Qin Dynasty in China, such as the Qin swords and the Yue King Goujian sword.
In 1932, the "memory" effect was first observed by Swede "Olander" in a gold-cadmium alloy. This effect means that after the alloy's shape is changed, it magically returns to its original shape once heated to a certain transition temperature. Alloys with this special function are called shape memory alloys. Shape memory alloys have only been developed for over 20 years, but due to their highly effective applications in various fields, they have attracted worldwide attention and are hailed as "magical functional materials."
In 1963, "Biller" at the US Naval Ordnance Laboratory discovered during research that within a temperature range significantly above room temperature, a NiTinol wire, when burned into a spring, then straightened in cold water or cast into shapes such as squares and triangles, would revert to its original spring shape when placed in water above 40℃. Subsequently, it was discovered that certain other alloys also had similar functions. This type of alloy is called a shape memory alloy. Each shape memory alloy composed of certain elements in a certain weight ratio has a transition temperature; above this temperature, the alloy is processed into a certain shape, then cooled below the transition temperature, and its shape is artificially changed. When heated above the transition temperature again, the alloy will automatically revert to the shape it was processed into above the transition temperature.
In 1969, the "shape memory effect" of NiTinols was first applied industrially. A unique pipe joint device was used. To connect two metal pipes that need to be joined, a shape memory alloy with a transition temperature lower than the operating temperature was selected. At a temperature above its transition temperature, it was made into a short pipe (used as a connector) with an inner diameter slightly smaller than the outer diameter of the pipes to be joined. Then, below its transition temperature, its inner diameter was slightly expanded. When the connected pipes were placed at the connector's transition temperature, the connector automatically contracted and fastened the connected pipes, forming a strong and tight connection. The United States used a NiTinol connector in a certain jet fighter's hydraulic system, and there have never been any oil leaks, detachments, or damage incidents.
On July 20, 1969, American astronauts landed on the moon in the Apollo 11 lunar module, leaving the first human footprints on the moon and transmitting information between the moon and Earth through a hemispherical antenna several meters in diameter. How was this enormous antenna brought to the moon? It was made of a shape memory alloy material, first processed to the required specifications above its transition temperature, then its temperature was lowered and it was compressed into a ball, packed into the lunar module and taken to space. After being placed on the moon, under sunlight, it reached the alloy's transition temperature, and the antenna "remembered" its original appearance, transforming into a huge hemisphere.
Scientists have added other elements to NiTinols and further researched and developed new NiTinol-titanium shape memory alloys such as NiTinol-copper, titanium-NiTinol-iron, and titanium-NiTinol-chromium; in addition, there are other types of shape memory alloys, such as copper-NiTinol alloys, copper-aluminum alloys, copper-zinc alloys, and iron-based alloys (Fe-Mn-Si, Fe-Pd), etc.
Shape memory alloys also have broad application prospects in bioengineering, medicine, energy, and automation.
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