Surface properties and mechanism of corrosion resistance enhancement in a high temperature nitrogen ion implanted medical grade Ti

The surface characteristics and mechanism of corrosion resistance enhancement in a high temperature nitrogen ion implanted medical grade Ti was investigated. The implantations were carried out in a constant energy (80 keV) and dose (2.1 x 10(+18) Ion cm(-2)) at room temperature (similar to 300 K, without heating the substrate) and at different elevated temperatures (473 K, 673 K and 873 K by external heating of the substrate). For implantation temperature optimization, the nitride phase formation on the implanted samples was characterized using grazing incidence X-ray diffraction (GI-XRD) method and also the electrochemical polarization tests in the Ringer's solution as a simulated body fluid were carried out. A significantly enhanced corrosion resistance was achieved for the titanium sample implanted at 473 K between different implantation temperatures, which was attributed to the higher protective performance of the nitride layer over this sample, resulted from the accelerated formation of uniform and dense nitride phases on its surface. The corroded surface of the samples was observed by a field emission scanning electron microscope (FE-SEM). Several delaminations and detachments in the nitride layer were observed over the room temperature implanted sample, however the 473 K implanted sample was relatively intact. The deteriorated corrosion resistance of the 673 K and 873 K samples was attributed to the non-uniformity of the surface and phase transition from a to (3 Ti, respectively. For the 473 K implanted sample as a selected implantation temperature, the enhanced corrosion resistance mechanism was investigated more accurately. The surface layer of 473 K implanted sample was studied by a Multi-Beam Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) and was compared with an unimplanted and a 300 I( implanted sample. The cross section of samples was channeled using FIB method to study the distribution of nitrogen atoms by EDS mapping technique. The depth profiles of the nitrogen atoms in the implanted samples were also obtained from EDS-analysis. Surface feature and roughness of samples were studied by atomic force microscopy (AFM). According to the AFM results, the surface of 473 K implanted sample with uniformly distributed nano-scaled islands, showed a higher roughness value compared to the 300 K implanted one and was predicted to have more compatibility with body tissues. Electrochemical behavior of unimplanted, 300 K and 473 K implanted samples was studied using impedance spectroscopy methods in the Ringer's solution as a simulated body fluid. The mechanism of the corrosion resistance improvement at high temperature implanted sample was developed according to the impedance spectroscopy results. (C) 2016 Elsevier B.V. All rights reserved.