Nitinol is one of the most extraordinary metals to be discovered this century: A simple alloy of nickel and titanium, nitinol has some perplexing properties. A metal with a memory, it can be made to remember any shape into which it is fashioned, returning to that shape whenever it is heated.
For example, a piece of nitinol wire bent to form a circle that is then heated and quenched will remember this shape. It may then be bent or crumpled, but on reheating, will violently untwist, reforming its original shape. This remarkable ability is called Shape Memory Effect (XXXXXE); other alloys, such as brasses, are known to possess it to a limited extent. No one fully understands XXXXXE, and nitinol remains particularly perplexing, for,? whenever it performs this peculiar feat, it appears to be breaking the laws of thermodynamics by springing back into shape with greater force than was used to deform it in the first place.
But not only is nitinol capable of remembering, it also has the ability to "learn". If the heating-cooling-crumpling-reheating process is carried out sufficiently often, and the metal is always crumpled in exactly the same way, the nitinol will not only remember its original shape, but gradually it learns to remember its crumpled form as well, and will begin to return to the same crumpled shape every time it is cooled.
Eventually, the metal will crumple and uncrumple, totally unaided, in response to changes in temperature and without any sign of metal fatigue.?
Engineers have produced prototype engines that are driven by the force of nitinol springing from one shape to another as it alternately encounters hot and cold water. The energy from these remarkable engines is,however,not entirely free:heat energy is required to produce the temperature differences needed to run the engine. But the optimum temperatures at which the metal reacts can be controlled by altering the proportions of nickel to titanium; some alloys will even perform at room temperature. The necessary temperature range between the warm and the cold can be as little as twelve degrees centigrade.
鎳鈦合金鎳鈦諾是這個世紀(jì)所發(fā)現(xiàn)的最不尋常的金屬之一，作為鎳和鈦的簡單的一種合金，鎳鈦諾具有一些令人驚嘆的特征。這是一種有記憶力的金屬，人們可以使它記住它被 塑成的任何形狀，并在加熱后恢復(fù)這一形狀。比如，一節(jié)鎳鈦諾線圈在加熱冷卻后會記住 圓圈這形狀。
隨后它可能被彎折成其它形狀，但一旦再次加熱，就會迅速地自動恢復(fù)成最初的圓圈狀。 這種不尋常的能力被稱為形狀記憶效果(XXXXXE)。其它一些合金如黃銅在一定程度上也具有這種特性。目前人們對XXXXXE這一特性尚缺乏透徹的認(rèn)識，而鎳鈦諾尤其使人驚奇，因為每當(dāng)它展現(xiàn)這一驚人的功能時，似乎都違背了熱力學(xué)原理。因為它在恢復(fù)原 有形狀時所釋放的力比人們使它變形所施加的力大得多。
鎳鈦諾不僅有記憶力，還能"學(xué)習(xí)"。 如果加熱-冷卻-彎曲-再加熱這一過程重復(fù)一定次數(shù)，且每次冷卻后它都被絲毫不差地彎成同一形狀，它不僅可以記住最初的形狀，還能逐漸記住它被彎成的形狀，并開始在每次冷卻時恢復(fù)這一形狀。
最終，它會自動地隨溫度變化而彎曲和恢復(fù)這些形狀，并且沒有任何 疲勞跡象。 工程師們已制造出一些發(fā)動機樣機，利用鎳鈦合金在交替遇熱水和冷水時迅速改變形狀所產(chǎn)生的力做推動力。然而這些神奇的發(fā)動機工作時并非完全不耗能，因為必須有熱能來制造溫差才能使機器運轉(zhuǎn)。
但人們可以通過改變合金中鎳鈦的比例來控制使它反應(yīng)的最佳溫度。有的鎳鈦合金甚至能在室溫下做出反應(yīng)，冷暖之間的最小溫差只有 12℃。
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