Nitinol , in a percentage ratio of 45% (titanium) - 55% (nickel) and with an equal number of atoms of each substance. The name was obtained from a combination of the formula (NiTi) and the abbreviation of the name of the place where it was developed ( N aval О rdnance L aboratory → NOL). Unusually, this compound has the property of shape memory . If a part of complex shape is heated to red heat, then it will remember this shape. After cooling to room temperature, the part can be deformed, but when heated above 40 ° C it will restore its original shape. This behavior is due to the fact that, in fact, this material is an intermetallic compound , and not a classical alloy, and the properties of the starting materials (Ni, Ti) are practically not expressed in it. It makes it unique because of which, when quenching, the mutual arrangement of atoms is ordered, which leads to the memorization of the form.
Content
History
In 1948, Soviet metallurgists G.V. Kurdyumov and L.G. Handros proposed an alloy endowed with the ability, after significant plastic deformations, to restore its original shape when heated to a certain temperature. In 1980, this invention was recognized as a discovery and became known as the Kurdyumov effect (the effect of restoring a given configuration or the shape memory effect). In 1962, William Bühler, together with Frederick Wang, discovered the properties of this alloy during a study in the naval laboratory. Although the potential use of nitinol was immediately recognized, real attempts to commercialize the alloy occurred ten years later. This delay has arisen largely due to the extreme difficulty of melting, processing and processing the alloy.
The discovery of the shape memory effect as a whole dates back to 1932, when the Swedish researcher Arne Olander was the first to notice this property in gold-cadmium alloys. The same effect was found in copper-zinc alloys in the early 1950s.
Production [1] [2]
Alloy production is a rather complex process consisting of several stages:
- Melting
- Remelting
- Casting
- Shaping
Production is complicated by the fact that to obtain a high-quality alloy, it is necessary to carefully check the number of primary components, and during melting, titanium easily interacts with gases [3] , which is why melting is carried out using the vacuum-induction method and vacuum-arc remelting. Also, the heat treatment of nitinol requires high accuracy, since the duration and temperature strongly affect the phase transformation temperatures.
In the vacuum-induction method, the initial ingot is prepared in graphite furnaces. This makes it possible to obtain a well-mixed alloy, but a certain amount of a compound of Titanium with Carbon occurs. Vacuum arc remelting is necessary to reduce the content of impurities and inclusions, as well as to provide the necessary cast structure. This is followed by casting to obtain blanks and shaping the blanks.
Properties [4]
Physical Properties:
- density - 6450 kg / m 3 ;
- melting point - 1300 ° C;
- superelasticity - 20 times higher than steel;
Technical Properties:
- high corrosion resistance ;
- recovery internal stress - 800 MPa;
- permissible deformation - 8%;
- permissible stretching - up to 12%;
- tensile strength - 1000 MPa;
- shape memory ;
Application
The material is used in medicine, in particular for the treatment of patients with diseases and injuries of the musculoskeletal system: funnel chest deformity (“shoemaker's chest”), vertebral fractures, Hallux Valgus (bumps on the legs). It is also used in dentistry for orthodontic treatment: the metal arches of the bracket systems are made of this material. [5] [6]
Notes
- ↑ Nitinol - production, processing and characteristics (08/11/2014).
- ↑ Nickel-titanium alloy tools used in endodontics. .
- ↑ Features of the melting of titanium alloys . All about metallurgy. Date of treatment July 25, 2019.
- ↑ Metal and memory (04/11/2017).
- ↑ A world without pain
- ↑ "Living great!"