Alloying of nickel and titanium yields an intermetallic — Nitinol — known primarily for its ability to move (a.k.a. muscle wire) when its temperature changes. Just like ice is a different crystal arrangement of water, nitinol undergoes a change its crystal arrangement at specific temperature points, defined by the alloy composition and manufacturing process.

The phases of most use to us are the martensite and the austenite crystal arrangement. Martensite is the colder (referred to as 'mother' phase) and austenite is the higher temperature phase. Nitinol's transition between the two phases occurs over a gradient of several degrees centigrade (usually about 10º). When choosing a nitinol product for your application, you will come across the following terms:

• M_f: martensite (finish): nitinol is fully martensite at and below this temperature. For wire, it will be very soft and pliable, with an elastic modulus of 28-40 GPa. Its thermal conductivity is greatly reduced.
• M_s: martensite (start): the alloy just begins to transition from its austenite state. Nitinol wire (unmodified stock from us) will loose their rigidity and become more pliable.
• A_s: austenite (start): the material will begin to stiffen and usually change shape - stock unmodified wire will begin to unfurl and straighten out.
• A_f: austenite (finish): We use the A_f value when indicating the "transition phase" of our alloys. Typical values range from 10ºC to 80ºC and suit a variety of needs. A cold wire subjected to a temperature equivalent to its A_f or above will result in a fast crystal transformation. Our wires will immediately spring straight (if not heat treated into a different configuration). The wire acts more like spring steel; its elastic modulus changes to 75-83 GPa, and its thermal conductivity is doubled.

Update (09.26.18): Online service restored. To all customers that were affected and the order canceled, we welcome to you to re-submit your order. All nitinol wires displayed on the product page are in stock ready to ship within 24 hours of order receipt. If you were affected by the website downtime, we welcome you to use code 'back4more' to obtain a 5% discount off your order total. Browse all Nitinol Products here.