Shape Memory Alloys (SMA’s) By Chris Bomersbach MEEN 3344

Major Developments Buehler’s discovery of an NiTi alloy (Nitinol) in 1962, formed the basis for commercial use. Before then shape memory alloys had been observed but where not affective enough for practical use. SMA’s have seen commercial use since the late 1980’s when they where first used for coupling on oil pipes.

Types One way SMA’s are the most common type and can be deformed when cool, but upon heating, they return to their trained shape. Two way SMA’s can be trained to have a cool shape as well as a hot one. Different types include Ag-Cd 44/49 at.% Cd Au-Cd 46.5/50 at.% Cd Cu-Al-Ni 14/14.5 wt.% Al and 3/4.5 wt.% Ni Cu-Sn approx. 15 at.% Sn Cu-Zn 38.5/41.5 wt.% Zn Cu-Zn-X (X = Si, Al, Sn) Fe-Pt approx. 25 at.% Pt Mn-Cu 5/35 at.% Cu Fe-Mn-Si Pt alloys Co-Ni-Al Co-Ni-Ga Ni-Fe-Ga Ti-Pd in various concentrations Ni-Ti (~55% Ni The two underlined alloys are by far the most common. Cu-Al-Ni for being cost effective, and Ni-Ti for working better. http://en.wikipedia.org/wiki/Shape_memory_alloy

Ni-Ti This video of one way Nitinol can give you an idea of just how effective it can be compared to conventional metals. http://www.youtube.com/watch?v=fsBHF_j2FJ4&feature=related Nitinol can also be returned to it’s original shape by sending an electric current through it. As it resists the electricity, it becomes heated. I think It’s interesting to note that basically the same alloy that was originally put to commercial use is still the most common today.

Pseudo Elasticity The most common commercial application involves the pseudo-elastic property during it’s high temperature state. This includes eye-glasses, cell phone antennas, and so on, which are experiencing their high temperature state at room temperature.

Future Applications In the future, if significant steps can taken in cost reduction, SMA’s will be used for almost every metal object. Mail boxes could pop back into shape on a sunny day. That slinky you had as a child would have lasted longer then thirty minutes. Imagine getting into a car wreck, then only needing to hold a torch to your vehicle to repair the damage. There are endless new uses for Biomedical applications, such as surgical equipment and mechanical devices. There could also be morphing airplanes and submarines that could increase efficiency at different speeds.

References http://www.bio-medicine.org/biology-technology-1/Re-Shaping-the-Future-with-Shape-Memory-Alloys---SMA-Starter-Kit-10282-1/ http://www.prudentpressagency.com/modules/news/article.php?storyid=8180 http://smart.tamu.edu/ http://www.stanford.edu/~richlin1/sma/sma.html