2025/04/23

What is shape memory alloy?

Shape memory alloys are alloys that can automatically recover their plastic deformation to their original shape at a specific temperature. In addition to their unique shape memory function, memory alloys also have excellent characteristics such as wear resistance, corrosion resistance, high damping, and superelasticity. The elongation rate is over 20%. The fatigue life reaches 107 times, and the damping characteristics are 10 times higher than ordinary springs. Its corrosion resistance is superior to the currently better medical stainless steel, so it can meet the application needs of various engineering and medical fields, and is a very excellent functional material. High-quality memory alloy wires can be produced and applied to fields such as spectacle legs, women's bras, mobile phone antennas, women's IUDs, orthodontic wires, instruments and meters. In 1963, the US Navy Ordnance Research Laboratory needed some NiTinol wires in an experiment. The alloy wires they received were all bent and curved. For ease of use, these bent and curved thin wires were straightened one by one before use. A strange phenomenon appeared in subsequent experiments: when the temperature rose to a certain value, these alloy wires, which had been straightened, suddenly magically and quickly returned to their original bent and curved shape, and were exactly the same as the original shape. Repeated experiments many times, the results were exactly the same each time. The straightened alloy wires, as long as they reached a certain temperature, immediately returned to their original bent and curved appearance. It's as if they were "frozen" and lost consciousness in the past, and their shape was changed by people. When the temperature rises to a certain value, they suddenly "wake up" and "remember" their original appearance, so they desperately restore their "original appearance". The crystal structure of NiTinol is different above and below 40°C, but when the temperature changes around 40°C, the alloy will contract or expand, causing its shape to change. Here, 40°C is the "transformation temperature" of NiTinol-titanium memory alloy. Various alloys have their own transformation temperatures. Memory alloys have been used in pipeline joining and automation control. Sleeves made of memory alloys can replace welding. The method is to fully expand the pipe ends by about 4% at low temperature. When assembling, they are connected together. Once heated, the sleeve contracts and recovers its original shape, forming a tight joint. The hydraulic system of US Navy aircraft uses 100,000 such joints, and no oil leakage or damage has occurred for many years. For damaged ship and submarine oil pipeline, it is very convenient to repair them with memory alloy fittings. In some places where construction is inconvenient, pins made of memory alloy are inserted into the holes and heated, and their tail ends automatically separate and curl, forming a single-sided assembly. Memory alloys are particularly suitable for thermomechanical and isothermal automatic control. Room temperature automatic opening and closing arms have been made, which can open ventilation windows during the day when exposed to sunlight and automatically close them at night when the room temperature drops. There are also many design schemes for memory alloy heat engines. They can all work between two media with low temperature difference, thus opening up new ways to utilize industrial cooling water, nuclear reactor waste heat, ocean temperature difference, and solar energy. The current common problem is low efficiency, only 4%~6%, which needs further improvement. The application of memory alloys in medicine is also very attractive. For example, bone plates used for bone setting can not only fix the two broken bones, but also generate compressive force in the process of restoring their original shape, forcing the broken bones to join together. Orthodontic wires used in dentistry, long clips for ligating cerebral aneurysms and vas deferens, and support plates for spinal straightening are all activated by body temperature after being implanted in the human body. The thrombus filter is also a new memory alloy product. After the straightened filter is implanted into the vein, it will gradually recover into a net shape, thereby preventing 95% of blood clots from flowing to the heart and lungs. An artificial heart is a more complex organ. The muscle fibers made of memory alloy cooperate with the elastic film ventricle to simulate the ventricular contraction movement. Pumping water has been successfully achieved. Because memory alloy is a "living alloy", using its shape change at a certain temperature, various self-control devices can be designed, and its uses are constantly expanding.

2025/04/23

Medical applications of nitinol tubes

Medical Applications of Nitinol Tubing Nitinol tubing is an intermetallic compound composed of approximately equal atomic ratios (50% NiTinol atoms and 50% titanium atoms), with a density of 6.45 g/cm³ and a melting point of 1240-1310℃. It possesses a two-phase crystal structure of martensite and austenite, which transform into each other under certain conditions, exhibiting shape memory effect and superelasticity—two important functionalities in medical applications. Nitinol tubing should be welded using 304 stainless steel. The nitinol tubing should be 1.8mm * 1.4mm. The stainless steel should be 2.5mm * 1.8mm. During welding, the nitinol tubing is inserted into the stainless steel tube, with a depth not exceeding 4mm. Due to the thermal brittleness of nitinol tubing, the welding process is easily interrupted. Nitinol tubing is a shape memory alloy. Shape memory alloys are special alloys that can automatically recover their plastic deformation to their original shape at a certain temperature. With an expansion rate exceeding 20%, a fatigue life as high as 1*10⁷, damping characteristics 10 times that of ordinary springs, and corrosion resistance superior to currently used medical-grade stainless steel, it meets the needs of various engineering and medical applications, making it an excellent functional material. Keywords: Nitinol memory alloy flat wire_memory alloy wire_Nitinol memory alloy plate_Nitinol memory alloy wire_memory alloy flat wire_memory alloy plate_Nitinol memory alloy

2025/04/23

What is the principle of shape memory alloy?

Shape memory alloy principle: It is generally believed that shape recovery occurs when a complex rhombohedral crystal structure transforms into a simple cubic crystal structure. When the shape memory alloy recovers its original shape, it generates a tremendous force, as high as 60 kg/mm² for Nitinol, far exceeding the initial force applied during deformation. Generally, it can reach ten times the original deformation, meaning that the output energy is much greater than the input energy. Scientists cannot explain this. Physicist Roshall said, "There is nothing wrong with the laws of thermodynamics, but these laws simply do not apply to Nitinol.". Currently, many scholars believe that the shape memory alloy can recover its original shape due to the effect of "memory factors." The "memory factor" is derived through the study of free energy and volume relationship during the phase transition process.

2025/04/23

The promotion and application of NiTinol-titanium memory alloys in the medical industry

Nitinol is a shape memory alloy. Shape memory alloys are special alloys that can automatically recover their original shape from plastic deformation at a specific temperature. Its elongation rate is over 20%, fatigue life reaches 1*10^7, and damping characteristics are 10 times higher than ordinary springs. Its corrosion resistance is superior to the best currently available medical stainless steel, therefore it can meet the application needs of various engineering and medical fields, and is a very excellent functional material.

2025/04/21

Applications of Nitinol memory alloy springs

The spring is made of TiNi shape memory alloy wire, utilizing the one-way memory effect of shape memory alloys. After being stretched, it can automatically recover its original length as the temperature rises. This type of spring is also a typical structural form of industrial shape memory alloy components. After stretching, using hot water or hot air as a heat source, the temperature at which it returns to its original length is 65℃-85℃, and the original length is 80mm. The martensite phase (i.e., the phase organization at low temperature, where low temperature refers to room temperature) of the shape memory alloy is a soft phase, and the parent phase (i.e., the phase organization at high temperature, where high temperature refers to 65℃-85℃) is a hard phase. Uses: Shape memory alloys have a wide range of applications. For example, in machinery: clamping pins, pipe joints; in electronic instruments and equipment: fire alarms, connectors, soldering of integrated circuits; in medicine: artificial heart valves, spinal correction rods, skull repair and shaping, orthodontic treatment, and maxillofacial repair surgery, etc. It will also play a magical role in communication satellites, color televisions, temperature controllers, and toys, and will become a new type of material in modern navigation, aviation, aerospace, transportation, light textile, and other fronts. Shape memory alloys have been used in pipeline connection and automation control. Sleeves made of shape memory alloys can replace welding. The method is to fully expand the pipe end by about 4% at low temperature. During assembly, they are connected together. Once heated, the sleeve shrinks and recovers its original shape, forming a tight connection.

2025/04/20

Characteristics of NiTinol-titanium shape memory alloy

Shape Memory Effect: NiTinol-titanium (NiTi) shape memory alloys, after undergoing specific heat treatments, automatically recover their original shape. This characteristic is known as the shape memory effect. Shape memory can be categorized into one-way shape memory effect, two-way shape memory effect, and full shape memory effect based on the recovery conditions. Superelasticity: When subjected to external forces, NiTi shape memory alloys deform. Upon removal of the external force, they return to their original shape. This is the superelasticity of NiTi shape memory alloys. Superelastic deformation in NiTi alloys leads to martensitic transformation, while removal of the external force causes reverse martensitic transformation. Damping Capacity: The excellent damping capacity of NiTi shape memory alloys stems from the self-adjustment of phase transformation and the interfaces and movement generated during the transformation. Electrical Resistance: In NiTi shape memory alloys in the martensitic phase, the relationship between electrical resistance and strain is linear during deformation. After phase transformation, the slope of the curve decreases; however, a linear relationship is maintained before and after the martensitic phase transformation.

2025/04/20

The function of NiTinol-titanium shape memory alloy

In addition to its unique shape memory alloy properties, NiTinol also possesses advantages such as superelasticity, wear resistance, and corrosion resistance, leading to its widespread application in various fields. (1) Mechanical Engineering The initial application of NiTinol-titanium shape memory alloy in the mechanical industry was in pipe fittings and fasteners. Specifically, in the connection of mechanical parts and pipelines, such as the interface for in-flight refueling of aircraft, NiTinol-titanium shape memory alloy is processed into a sleeve with an outer diameter 3% larger than its inner diameter. At a certain temperature, the sleeve's diameter is expanded by approximately 8%. During assembly, the sleeve is taken out of liquid nitrogen, and the pipe is inserted from both ends. When the temperature rises to room temperature, electric heating can be used to change the temperature. The NiTinol-titanium shape memory alloy deforms at the in-flight refueling interface, and the sleeve made of NiTinol-titanium shape memory alloy contracts to form a tight seal, achieving a tight, leak-proof effect far superior to traditional welding. Therefore, NiTinol-titanium shape memory alloy is particularly suitable for aerospace, shipbuilding, oil pipelines, and other fields. In locations where construction is inconvenient, NiTinol-titanium shape memory alloy can be used to make pins, which are inserted into holes and heated. Therefore, using the temperature-sensitive driving multiple functions of NiTinol-titanium shape memory alloy, robots and manipulators can be made. (2) Construction Industry As mentioned earlier, the various characteristics of NiTinol-titanium shape memory alloy, combined with its structure, can enhance the system's damping and reduce the dynamic response of the structure, thus creating various forms of damping energy dissipation devices. NiTinol-titanium shape memory alloy can also be used to design vibration isolators. By increasing the energy dissipation of deformation through the deformation of the NiTinol-titanium shape memory alloy, the transmission of seismic energy from the structure to the upper structure is prevented, thus protecting the upper structure and truly enhancing the seismic performance of the structure. (3) Aerospace Industry In aircraft hydraulic systems, almost every aircraft requires the use of eight hundred NiTinol-titanium shape memory alloy connectors. Since the 1970s, most US Navy aircraft have used this type of pipe fitting without any failure record. In addition, NiTinol-titanium shape memory alloy can also be used in spacecraft antennas and electromechanical actuators. (4) Automotive Industry NiTinol-titanium shape memory alloy is mainly used in engine heat dissipation fan clutches, exhaust nozzles, and diesel radiator. (5) Medical Field NiTinol-titanium shape memory alloy possesses high mechanical properties and biocompatibility, making it widely used in the medical field. For example, in orthodontics, cosmetic surgery, minimally invasive cardiovascular procedures; thrombus filters are actually a new product of NiTinol-titanium shape memory alloy; the straightened filter, after being implanted in the vein, gradually forms a network over time, preventing more than 90% of blood clots from flowing to the heart, lungs, and other organs. In addition, NiTinol-titanium shape memory alloy is also used in medical clinical trials for surgical sutures, artificial joints, and artificial hearts.

2025/04/18

Memory metal manufacturing companies introduce the applications of memory alloys and the special properties of NiTinols.

Memory metal manufacturing companies introduce the applications of memory alloys and the special properties of NiTinols. Memory alloys have many successful applications in aerospace. For example, large antennas on satellites can be made of memory alloys. Before launching a satellite, the parabolic antenna is folded and placed inside the satellite. After the rocket launches and sends the satellite into its predetermined orbit, it only needs to be heated, and the folded satellite antenna will naturally unfold due to its "memory" function, restoring its parabolic shape.

2025/04/18

Shape memory alloy classification

Shape memory alloys (SMAs) have the ability to recover their shape due to the thermoelastic martensitic phase transformation that occurs within the material during deformation. SMAs have two phases: the high-temperature austenite phase and the low-temperature martensite phase. Depending on the different thermal and mechanical loading conditions, SMAs exhibit two types of properties. Shape Memory Effect One-way memory effect: When a shape memory alloy is deformed at a lower temperature and heated, it recovers its shape before deformation. This shape memory phenomenon that only exists during heating is called the one-way memory effect. Two-way memory effect: Some alloys recover their high-temperature phase shape when heated and their low-temperature phase shape when cooled, which is called the two-way memory effect. Full memory effect: When heated, it recovers the high-temperature phase shape, and when cooled, it becomes a low-temperature phase shape with the same shape but opposite orientation, which is called the full memory effect. The shape memory effect of SMA originates from the thermoelastic martensitic phase transformation. Once this martensite is formed, it will continue to grow as the temperature decreases. If the temperature rises, it will decrease and disappear in a completely opposite process. The difference between the two free energies serves as the driving force for the phase transformation. The temperature T0 where the two free energies are equal is called the equilibrium temperature. Martensite phase transformation will only occur when the temperature is below the equilibrium temperature T0, and vice versa, the reverse phase transformation will only occur when the temperature is above the equilibrium temperature T0. In SMAs, martensitic transformation is not only caused by temperature but also by stress. This stress-induced martensitic transformation is called stress-induced martensitic transformation, and the transformation temperature has a linear relationship with stress. SMA systems discovered so far: 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. Pseudoelasticity When a shape memory alloy in the high-temperature austenite state undergoes a large deformation under external force, the large deformation is completely recovered after the external force is removed. However, the stress-strain curve is not linear during the deformation process, and dissipative energy will be generated.

2025/04/18

The origin of shape memory alloys

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."