Surface modification of Ni-Ti alloy by low-temperature nitriding process

Abstract
In order to create new applications and enhance the performance of NiTi alloys, surface modifications are important to improve their biocompatibility. TiN coatings, due to its low chemical reactivity, high hardness and resistance to wear and corrosion, have been adopted for protecting surface of the NiTi alloys. In presented work the structure of layers formed at surface of the NiTi alloy was reported. The layers were formed using glow discharge technique at low temperature: 300 - 400°C. Thickness, surface roughness, interface roughness, density were calculated using reflectivity measurement. The X-ray grazing diffraction was applied for phase analysis. The chemical composition was determined using the XPS method. Corrosion resistance was studied applying the potentiodynamical method. Electrochemical characteristics of the samples were measured at the room temperature in Tyrod’s solution. Results have shown that low temperature nitriding produced the layers, which consisted from the nanocrystalline TiN phase. Relatively high values of corrosion and breakdown potentials proved that the TiN layers as well as the intermediate Ti₃Ni phase effectively protect surface of the NiTi alloys against nickel ion release.