Ti-Ni Alloy System
All phases show anistrophic elasticity in different crystallographic reactions
Equilibrium Phase Diagram of Ti-Ni 
The elastic modulus and Vicker's hardness of Ti-Ni system decrease in the following order ;
NI3TI>B2_NITI>B19_NITI>NITI2
Ti-Ni system consists of intermetallic compounds
Ti-Ni alloy exhibit two different temperature-dependent crystal structure (phases)
microstructure of Ti-Ni alloy 
the pair interactions are first restricted to FCC based structures
At low temperature, the phase become martensite
At high temperature, the phase become austenite
When martensite Ti-Ni is heated, it will transform into austenite
The starting temperature is called austenite start temperature (As)
The ending temperature is called austenite finish temperature (Af)
When austenite Ti-Ni is cooled, it will transform into martensite
The starting temperature is called martensite start temperature (Ms)
Application of Ti-Ni Alloy in Industry 
The ending temperature is called martensite finish temperature (Mf)
The nickel–titanium alloy or known as Nitinol has been used in the manufacture of endodontic instruments.
Nitinol alloys have greater strength and a lower modulus of elasticity compared with stainless steel alloys. The super‐elastic behaviour of Nitinol wires means that on unloading they return to their original shape following deformation.
These properties are of interest in endodontology as they allow construction of root canal instruments that utilize these favourable characteristics to provide an advantage when preparing curved canals.
Nitinol alloy usually contains 55% nickel and 45% titanium
Ni and Ti are both alloying elements in steels and other alloys
Ti is a strong carbide former and also
promotes the ordered Ni3Al phase in Ni-based superalloys. :
In the binary Ti-Ni diagram the hexagonal D024
is more stable than the L12 phase and there is an ordered B2 phase stable in the middle.