We had a piece of this thin Shape Memory Alloy in class, (I think it was called nitinol, but I think thats a brand name) the teacher showed how it is very flexible and springy, and will return to it's original shape when placed in warm water. Normal metals, when bent forward and back, will work harden then break, will a SMA break like this? Would the work hardening be undone by returning it to it's original shape?
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$\begingroup$ These guys use nitinol as an electric "muscle". A small current passed through nitinol causes it to heat slightly and contract a remarkable amount for the small temperature difference. The shrink is used to allow the user to shift the focal plane of the instrument axially. $\endgroup$– Selene RoutleyCommented Jul 12, 2016 at 0:17
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When we change the shape of a SMA, its internal crystalline structure rearranges itself to another form. But when we heat up the SMA, it uses the heat energy to rearrange its crystalline structure to its original form, thus regaining its original shape. In the end, you can say that the work done in hardening it will be undone when it returns to its original state.
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1$\begingroup$ According to your argument, you automatically anneal (unharden, if you like) the metal in cycling its shape. Just to throw in the key word that may help to relate it to how one usually undos work hardening. $\endgroup$– user73762Commented Mar 7, 2015 at 9:47