Synthesis of Porous Nanostructure NiTi Implant and Measurement of Thermomechanical Properties

NiTi is known as the most important material for manufacturing implants and medical devises duo to its shape memory and superelasticity properties, high energy damping, and high corrosion resistance.

In this project, the possibility of producing nanostructured NiTi implant with high porosity was investigated. For reaching to the nanoscale, the mechanical alloying process was done on Ti and Ni powder as raw materials. Mechanical alloying process and the possibility of reaching nanostructure or amorphous phase was investigated. Space holder technique was used for reaching a porous structure. Sintering process was planned in a way to inhibit grain growth as much as possible. The samples sintered at two different sintering times. The effect of grain size and secondary phases on mechanical properties and phase transformation temperatures was studied.

The results showed that milling for 50 h at 300 rpm has led to amorphous phase and nanocrystallite with 50 nm diameter. Using space holder technique with the appropriate amount of spacer and choosing proper sintering time and temperature, the specimens with 70% porosity were produced. Furthermore, nanoscale grain size can lead to R phase transition. In fact, one of the effects of reaching to nanostructure is occurring R transformation due to high dislocation density and high grain boundaries surface. Nanostructured sample with 70% porosity was shown 5% superelasticity in the cyclic pressure test.

As the results showed, one of the advantages of porous samples is their elastic modulus which is more similar to the bone than other metallic implants.