If a paper clip is bent out of shape and then heated it will go back to the original shape. First, how does this even work? Second, if heated up and a new shape is created what happens if this process of cooling, bending, reheating is repeated? Does it retain memory of both or just the last heated shape?
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You set the shape by heating it up to very high temperatures, usually glowing, and then bending it. This causes the crystal structure within the metal to change and set into this new shape. When you cool it down and then bend it cold the crystal structure does not change, it just bends. This is similar to a rubber band but it does not have the energy to snap back. By heating up the metal a bit you give it enough energy to bend back. The heat causes the atoms to jiggle back and forth enough to settle in the relaxed crystal structure again. I do not think you can actually bend it back and forth many times. The crystal structure does change a bit every time you bend it and heat it up. It will become more hardened and brittle over time. And this does limit the practical applications of memory alloys.
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