Is nitinol ductile?

The type of fibre with the potential of self-centering after undergoing deformation whilst showing a ductile behaviour is Nitinol (Nickel-Titanium) alloy. Nitinol has two basic properties: shape memory effect and super-elasticity.

Is nitinol a crystalline?

Background Information: Nitinol is a nickel titanium alloy (~50% Ni, ~50% Ti) which has two phases or crystalline structures, a high temperature (austenite) and a low temperature (martensite), shown in Figure 1. The low temperature phase is weaker, allowing the material to be bent and pulled out of shape.

What is the structure of nitinol?

At higher temperatures, Nitinol assumes a cubic crystal structure referred to as austenite (also known as the parent phase). At lower temperatures, it spontaneously transforms to a more complicated ‘monoclinic’ crystal structure known as martensite.

What is martensite and austenite phase?

Nitinol typically exhibits two phases: austenite and martensite. Austenite has a body center cubic structure and is stable at higher temperatures. Martensite is a monoclinic crystal which is stable at lower temperatures (Fischer et al., 2002).

Why does nitinol remember its shape?

When a SMA is in martensite form at lower temperatures, the metal can easily be deformed into any shape. When the alloy is heated, it goes through transformation from martensite to austenite. In the austenite phase, the memory metal “remembers” the shape it had before it was deformed.

When does the austenite phase transformation of nitinol occur?

Stress–strain–temperature diagram of Nitinol ( Guo et al., 2013 ). In the thermal shape memory region of Fig. 1 ( Guo et al., 2013 ), when Nitinol is cooled down below the martensite finish temperature ( Mf) along path O → A, complete austenite to martensite (twinned) transformation occurs.

What is the your phase of nitinol made of?

R phase – a rhombohedral phase of Nitinol that forms from the cubic austenite phase and is considered ano- ther martensite with a P3 crystal structure. The R phase often competes with the austenite–B199 martensite transformation. Shape memory – ability of a material to return to a pretrained geometry upon the application of heat.

What is the transition temperature of nitinol alloy?

Austenite Phase. Temperature is above transition temperature. The movement generated in this phase is cause by the crystalline structure returning to its non-stress state (cubic). The exact transition temperature varies depending upon the exact composition of the nitinol alloy; commercial alloys usually have transitional temperatures between 70C…

How is the physical movement of nitinol caused?

The physical movement of Nitinol is attributed to internal molecular restructuring. And because movement is generated on a molecular level, it is quite strong. Nitinol alloy has three distinct temperature phases: Martensitic Phase. Low temperature phase. The crystal structure is aligned and cubic.