Nickel titanium

Nitinol is a nickel -titanium alloy and the most famous representative of the shape memory alloys. The name Nitinol is an acronym for Nickel Titanium Naval Ordnance Laboratory. Nitinol was developed in 1958 at the Naval Ordnance Laboratory (USA ) by William J. Buehler and Frederick Wang.

Nitinol is an intermetallic phase of NiTi having an ordered cubic crystal structure is different from that of titanium and nickel. It consists mainly of nickel (about 55 % ), another large part titanium. The alloy is up to 650 ° C can be used, corrosion resistant and high strength, while maintaining pseudo- elastic up to about 8 % deformed.

About the alloy ratio can affect the transformation temperature. Alloys with a low transformation temperature of eg 0 ° C are colloquially called super elastic. At room temperature, superelastic material behaves like spring steel. A typical application is due to the large deformability and good corrosion resistance surgical tool, endoscopes or implants such as stents. An alloy with a high transformation temperature of, for example, 80 ° C is colloquially known as memory metal or shape memory metal. Objects made ​​of this alloy can be deformed at room temperature with little effort. Heated above the transformation temperature, take them back to the original shape. The basic shape can be memorized by annealing at about 500 ° C. A well-known example is the nitinol clip, which is used as a demonstration, but has no practical use. Typical applications include robotic actuators and valves.

Nitinol is expensive because the alloying should be done under vacuum and already negatively affect low impurities, the desired material are some. Because of the high price Nitinol is not used in mass-produced products.

Nitinol is very hard. Wires can be cut using wire cutters robust. Normal wire cutter or scissors are not suitable. The shaping is done by grinding or electrical discharge. Wires are produced by pulling through. Between each drawing process, the wire is annealed.

Paperclip made ​​of nitinol in hot water, again in paperclip shape

Properties

• Density: 6450 kg / m³
• Melting temperature: 1240-1328 ° C