In the world of smart phones, smart watches and even smart central heating, why not take a look at smart alloys? In particular shape memory alloys (SMAs). SMAs ‘remember’ their original shape after being exposed to temperature or electromagnetic fields. SMAs can change ‘shape, stiffness, position, natural frequency and other mechanical characteristics.’[1]
SMAs include nickel-titanium alloys, with this group’s generic name being Nitinol*, copper-aluminium-nickel, copper-zinc-aluminium, and iron- manganese-silicon alloys.
Nitinol was found to be a SMA back in 1961 and it ‘remembers’ its shape with structural changes on an atomic level.
Dr. Frederick E. Wang, an expert in crystal physics, found that Nitinol has phase changes while still a solid. Nitinol is in the martensite phase while under the transition temperature (which varies depending on the composition of the alloy). In this phase Nitinol can be bent into different shapes. By heating the metal (to around 500C) while it is bent, which fixes the ‘parent’ shape, the metal is then in the austenite phase where the atoms are arranged very regularly and compactly. Above the transition temperature, Nitinol reverts from the martensite to the austenite phase which changes it back into its parent shape. [2]
There are many interesting applications of Nitinol in military, safety and robotics with the medical sector taking a leading role: tweezers, orthodontic wires, and glasses frames that can be bent and then return to their original shape on warming. The last application sounds of particular use for everyday life, as long as the glass remains intact!
Other miscellaneous applications of shape memory alloys include use in household appliances and in clothing, from deep fat fryers to bra underwires.
*stands for Nickel Titanium Naval Ordnance Laboratory
References:
[1]Rogers, Craig. “Intelligent Materials.” Scientific American Sept. 1995: 154-157.
