have been frequently applied to aluminum, steel and Ti based alloys in order to improve the wear behavior of substrates. The hard coatings such as TiN, TiB, TiC, etc. Although the degradation behavior of those alloys has not been fully investigated yet, concerns on the poor wear resistance still exists. In last decades, many novel non-toxic and low Young’s modulus Ti-Nb, Ti-Zr, Ti-Ta, and Ti-Mo based alloys have been developed. Therefore, non-toxic, low Young’s modulus, and wear resistance Ti based materials for bone and tissue applications is much needed. Also, the poor wear resistance of Ti and its alloys is another main issue. However, its high Young’s modulus (around 100-120 GPa, whereas Young’s modulus of bone is varying in a range of 4-30 GPa) and the concern regarding the reverse effects of Al and V on the body limits the use in implant technologies. The Ti-6Al-4V alloy has been widely used in implant technologies.
Titanium (Ti) and its alloys are the most attractive metallic biomaterials used in biomedical applications due to their high strength, excellent corrosion resistance and favorable biocompatibility. However, when the polarization potential was higher than threshold, or the period of immersion in high oxidizing acid solutions was sufficiently long, then they were attacked and removed with a corrosion rate higher than untreated Ti–6Al–4V alloy. While the untreated alloy showed a passive behaviour, the laser treated layer showed high electrochemical inertia and low corrosion currents. The microstructures consisted mainly of a thin continuous layer of TiN followed by nearly perpendicular dendrites, and below this, a mixture of small dendrites and large needles with a random orientation.
For comparison, untreated samples were tested under the same conditions. The microstructure and corrosion behaviour of the nitrided samples were examined, using scanning electron microscopy, X-ray diffractometry (XRD), Tafel and cyclic polarization tests in 4 M HNO3 and immersion tests in 60% HNO3 solution. Laser gas nitriding of the Ti–6Al–4V alloy under a pure nitrogen environment of 30 l/min gas flow rate, was carried out with 500 mJ laser beams, produced by a Nd:YAG-pulsed laser at 5 mm defocused distance, and 1.5 mm/s sample traverse velocities.
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