TEM studies of the nitrided/oxided Ni-Ti surface layer

Area of Science:

• Materials Science
• Surface Engineering
• Biomaterials

Background:

• Nickel-titanium (NiTi) shape memory alloys are vital in biomedical applications.
• Protecting the NiTi surface is crucial for enhancing its performance and longevity.
• Titanium nitride (TiN) and titanium dioxide (TiO2) coatings offer excellent hardness and corrosion resistance.

Purpose of the Study:

• To investigate the structure of multilayer nitrided/oxided NiTi surfaces.
• To evaluate the effect of adding oxygen during nitriding on NiTi coatings.
• To assess the corrosion resistance of the modified NiTi surface.

Main Methods:

• Glow discharge nitriding of NiTi alloy at 1073 K.
• Controlled addition of oxygen at the end of the nitriding process.
• Characterization using transmission and scanning electron microscopy.

Main Results:

• Formation of a multilayer structure with nanocrystalline TiN grains and columnar grains.
• An intermediate Ti2Ni layer formed between the TiN coating and the NiTi substrate.
• Addition of oxygen resulted in a thin TiO2 nanograin layer on the TiN surface, with some amorphous phase present.
• The combined nitriding and oxidation process yielded a surface with enhanced corrosion resistance.

Conclusions:

• Multilayer TiN/TiO2 coatings on NiTi alloys can be effectively produced via glow discharge nitriding and subsequent oxidation.
• The developed coatings significantly improve the corrosion resistance of NiTi shape memory alloys.
• This surface modification technique holds promise for advanced NiTi-based applications requiring superior durability.