Shape-memory alloys can be made from three different combinations, or alloys - a copper-aluminium-nickel alloy, a nickel-titanium alloy, or less commonly, a zinc, copper, gold and iron alloy. The alloy being used in the video above is a nickel-titanium alloy, which is commercially produced as sold as ‘Nitinol’.
Nitinol was discovered in 1959 by William Buehler, a scientist at the US Naval Ordnance Laboratory, as he searched for materials that could be used in tools for dismantling magnetic mines. Nitinol didn’t end up being much help in that regard, but it's now widely used in medical technology, including "devices that maintain blood flow within an artery, implants that restore function to a failing heart valve and retrieval devices that remove life-threatening blood clots from deep within the brain", says US-based Nitinol manufacturer Memry on their website.
Shape memory alloys like Nitinol can be made up of one of two different crystal structures, depending on where they are sitting in relation to a certain, very important temperature, known as the ‘transformation temperature’. If the alloy is below this temperature, its atoms are organised in flexible lattices, which allows it to be bent in all kinds of shapes very easily. But once the metal is heated past its transformation temperature - which for a piece of Nitinol wire will be somewhere between 65 and 80°C - it automatically returns to its original shape.
“Once heated to the critical temperature, Nitinol shows its 'heat memory' as it transforms into the austenitic state, where the atoms become locked into their previous rigid arrangement,” says the Grand Illusions website. "When the metal springs into its remembered shape, it does so with so much force that it can be used to do actual work. Small motors have been built using Nitinol wire that passes through different temperatures. Solar panels on some satellites are raised into position by shape memory alloys, activated by the heat of the Sun.”
Here's another video, showing Nitinol wire returning to its original shape - "HOT":