Structure and properties of high temperature nitIn order to find new applications and enhance the performance of NiTi alloy, surface modifications is necessary condition for improving its biocompatibility. Nitride and oxide coatings, which are known from their low chemical reactivity, high hardness and good wear and corrosion resistance, were adopted for protecting the NiTi surface. The nitriding and oxidation processes reduce the nickel migration to the surface and improves the biocompatibility of the NiTi alloy. In the present work nearly-equiatomic NiTi (50,6 at.%Ni, Af =10°C) alloy was nitrided at 800^oC using glow discharge technique. Additionally, at the end of the nitriding some amount of oxygen was added. Combination of nitriding and oxidiation of the NiTi surface produces nitride/oxide complex layer of a nanocrystalline structure. The average thickness of the obtained layer was about 0,55 μm. The nitrided layer contains nanocrystalline TiN phase. Adding the oxygen at the end of the nitriding process creates TiO₂ phase on the top of the TiN layer. The layer of Ti₂Ni phase creates the interface between nitrided/oxidized NiTi surface and β-NiTi matrix. Small amount of an amorphous phase, between the nano-grains of nitride and oxide phase, was identified. The potentiodynamical studies in Tyrod’s solution show good corrosion resistance of the nitrided/oxidized NiTi surface proving its high quality.

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