Shape Memory Alloy

What is SMA?

Shape Memory Alloys (SMA) are a group of materials that exhibit two unusual properties: thermally induced shape recovery and super- or pseudo-elasticity. The latter means that an SMA in its elastic form can undergo a deformation approximately ten times that of a spring-steel equivalent, and full elastic recovery to the original geometry may be expected.

There are approximately 16 different metal alloys that exhibit shape recovery. Diameter exploits nickel-titanium alloy, often referred to as Nitinol; this alloy has the best mechanical properties of the various SMA alloy types.

The superelastic nickel-titanium (Ni-Ti) alloys are 'stressed' by simply working the alloy. These stresses can be removed, just as with many other alloys, by an annealing process. The stressed condition is termed stress-induced martensite, which is the equivalent of being cold/hot worked. Both the heat and elastic effect are due to a change or reorganisation of the basic structure of the alloy when heated, cooled or stressed.

Applications

The variety of forms and the properties of SMAs make them extremely useful for a range of medical applications. Nitinol is used in implanted devices and surgical instruments for example, as the properties allow one to constrain a wire or other form of material into a small package. A wire that in its 'deformed' shape has a small cross-section can be placed inside a catheter, which can enter inside the body by a small incision. The catheter is steered to an appropriate site and the SMA device is released, it now 'remembers' its shape and as it reforms it is capable of pulling together, pushing apart, dilating or constricting parts of the body, with precision and reliability. Needless to say, it has an excellent history of biocompatibility and adds significantly to the possibilities for treatment of disease or trauma.

Other applications of the metal alloy have been applied in the automotive, aerospace, IT, petroleum and chemical industries. A pencil-sized bar of SMA can be arranged to move several tons of load by heating. A satellite solar panel can be unfurled using SMA actuators heated by an electrical current, the choke or fuel enriching mechanism for cars or trucks, detects both cold and hot conditions for engine start-up until the engine achieves normal running temperatures with potential fuel saving and its subsequent improvement in exhaust emissions. Fuel and hydraulic line SMA connectors are commonly used on aircraft and in chemical industries where hot and aggressive media, such as acids, need to be reliably contained in pipe-work without leakage! 

Exploiting the unique material

Diameter has created a number of novel applications for these intriguing materials and has through its staff, more than twenty years experience in the application and qualification of SMA.

Diameter would be happy to assist or appraise your ideas for shape memory alloy and could help with design\manufacture of your products.