Shape-memory alloys

Shape-memory alloys are a group of metallic materials that can regain their original shape after 

Shape-memory alloys show a thermoelastic martensitic transformation. This is a martensitic transformation, as described above, but which, in addition, must have only a small temperature hysteresis, some 10s of degrees at most, and mobile twin boundaries, that is, ones that move easily. Additionally, the transition must be crystallographi-cally reversible. The importance of these characteristics will be clear when the mechanism of the shape-memory effect is described. 

The SME was first reported in 1951 involving a Au—Cd alloy (1). Many other alloys exhibiting this behavior have since been discovered some of these are Hsted in Table 1. It was, however, the discovery of the SME in the nominally equiatomic Ni—Ti alloy that led to commercial appHcations. This 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Ahoy Composition, atomic % Crystahographic stmeture change Hysteresis, AT, °C 

To determine the percentage of the remaining constituents, subtract from 100%.  

Ahoy Composition, at % Crystahographic stmeture change Ordering 

Alloy Composition, at % Crystallographic structure change 3 Ordering 

The intermetallic Ni-Ti system has the imusual property of after being distorted, returning to its original shape when heated. This was the first of the shape memory alloys (SMAs) and was discovered by accident at the Naval Ordnance Laboratory, hence its name Nitinol. Other SMAs include Cu-Al-Ni, Cu-Zn-Al, and Fe-Mn-Si alloys. The shape memory mechanism depends on a martensitic solid-state phase transition that takes place at a modest temperature (50°C—150°C), depending on the alloy. The high temperature phase is referred to as austenite and the low temperature phase is called martensite (following the terminology of the Fe-FeCa system). 

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PCTFEin [FLUORINECOMPOUNDS,ORGANIC - POLYCm.OROTRIFLUOROETTTfLENE] (Volll) -of shape-memory alloys [SITAPE-MEMORY ALLOYS] (Vol 21)... 

Shape anisotropy Shape control Shape factors Shape-memory alloys Shape-selective catalysis Shape selectivity Sharpless catalyst Shaving cream Shaving creams... 

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