Application Examples of Shape Memory and Superelastic Alloys

The unique properties of shape memory alloys make them the perfect choice (and often the only choice) for many applications. Most commercial applications of shape memory alloys can be grouped into three broad categories: Superelastic Devices, Shape Memory Actuation Devices, and Martensitic Devices.


Superelastic Devices

NiTi superelastic devices are used for applications which demand the extraordinary flexibility and torqueability of NiTi. NiTi has the ability to absorb large amounts of strain energy and release it as the applied strain is removed. The elasticity of NiTi is approximately ten times that of steel. NiTi also has excellent torqueability and kink resistance, which are important for medical guidewires. Further, superelastic NiTi alloys provide a constant force over a large strain range. This has been exploited in the field of orthodontics where a constant force enhances tooth movement with greater patient comfort. Examples of superelastic devices include:


Shape Memory Actuation Devices

Shape Memory Actuation Devices utilize the shape memory effect to recover a particular shape upon heating above their transformation temperatures. Shape memory actuation devices can act without constraint to freely recover their trained shape, can be fully constrained so that they provide a force, or can be partially constrained so that they perform work. The transformation temperatures of the NiTi alloy can be adjusted to activate at precisely the required temperature. Common actuation temperatures are human body temperature and boiling water temperature. Examples of shape memory actuation devices include:


Martensitic Devices

The martensitic phase of NiTi has some unique properties which have made it an ideal material for many applications. First, the martensitic phase transformation has excellent damping characteristics due to the energy absorption characteristics of its twinned phase structure. Second, the martensitic form of NiTi has remarkable fatigue resistance. Finally, the martensitic phase is easily deformed, yet will recover its shape upon heating above its transformation temperatures. Examples of martensitic devices include:


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