Improvement of tribological properties of Ti6Al4V by nitrogen plasma immersion ion implantation (original) (raw)
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IEEE Transactions on Plasma Science, 2000
Although titanium and its alloys own good mechanical properties and excellent corrosion resistance, these materials present poor tribological properties for specific applications that require wear resistance. In order to produce wear-resistant surfaces, this work is aimed at achieving improvement of wear characteristics in Ti-Si-B alloys by means of high temperature nitrogen plasma immersion ion implantation (PIII). These alloys were produced by powder metallurgy using high energy ball milling and hot pressing. Scanning electron microscopy (SEM) and X-ray diffraction identified the presence of α-titanium, Ti 6 Si 2 B, Ti 5 Si 3 , TiB and Ti 3 Si phases. Wear tests were carried out with a ball-on-disk tribometer to evaluate the friction coefficient and wear rate in treated and untreated samples. The worn profiles were measured by visible light microscopy and examined by SEM in order to determine the wear rates and wear mechanisms. Ti-7.5Si-22.5B alloy presented the highest wear resistance amongst the untreated alloys produced in this work. High temperature PIII was effective to reduce the wear rate and friction coefficient of all the Ti-Si-B sintered alloys.
Electrochemical behavior of the Ti6Al4V alloy implanted by nitrogen PIII
Surface and Coatings Technology, 2011
Plasma surface treatments have been used very often to enhance the surface properties of metallic materials. In this work, Ti6Al4V titanium alloy was treated by nitrogen plasma immersion ion implantation (NPIII) in order to obtain improvements in its surface properties, such as corrosion resistance evaluated here. The microstructure and corrosion behavior of the implanted and unimplanted samples were evaluated, using, XRD, GDOES and potentiodynamic polarization and impedance electrochemical spectroscopy tests in 0.6 M NaCl solution. It was verified that the NPIII created resistant layers to corrosive attacks. In corrosion tests by polarization, the implanted samples showed corrosion current density reduction of about 10 times compared to the Ti6Al4V alloy without treatment. Besides that, it was also observed a reduction of the passive current density of one order of the magnitude. In all the studied cases, the polarization curves were shifted to more positive values of potentials, indicating a lower tendency of these PIII treated surfaces to corrosion. The implantation process produced a thin TiN surface layer followed by Ti 2 N and then a layer with nitrogen in solid solution, all detected by GDOES combined with X-ray diffraction. These layers promoted an excellent polarization resistance of the Ti6Al4V surfaces on impedance spectroscopy tests also. This better performance in these tests can be correlated with the formation of continuous nitride layer, which could retard chloride ions ingress into the substrate.
Improved properties of Ti6Al4V by means of nitrogen high temperature plasma based ion implantation
Surface and Coatings Technology, 2011
A stable heating source, providing steady temperatures in the range of 200 to more than 1000°C, was used to perform high temperature plasma based ion implantation (PBII) on Ti6Al4V. The precise control of the heating of the samples in vacuum while performing PBII is accomplished by means of an efficient electron source, working independent of the conditions of the discharge. The electrons produced by a low work function (2.1 eV) barium, strontium and calcium oxide cathode help with the start-up of the discharge, with the increase of nitrogen ionization and heating of the samples. The large growth of the treated layer thickness was a result of the thermal diffusion of nitrogen, reaching up to 20 μm, in the total process time lasting only 100 min. Experiments were run by setting a constant substrate temperature during PBII to 800°C but varying the pulse intensity and the duration of the process. Our results showed improvements of the mechanical and tribological properties, and also higher resistance to corrosion of the samples treated by high temperature PBII.
Hybrid processing of Ti6Al4V using plasma immersion ion implantation combined with plasma nitriding
Materials Research-ibero-american Journal of Materials, 2006
Based on the fact that the Ti-6Al-4V alloy has good mechanical properties, excellent resistance to corrosion and also excellent biocompatibility, however with low wear resistance, this work aims to test plasma processes or combination of plasma and ion implantation processes to improve these characteristics. Two types of processing were used: two steps PIII (Plasma Immersion Ion Implantation) combined with PN (Plasma Nitriding) and single step PIII treatment. According to Auger Electron Spectroscopy (AES) results, the best solution was obtained by PIII for 150 minutes resulting in ~ 65 nm of nitrogen implanted layer, while the sample treated with PIII (75 minutes) and PN (75 minutes) reached ~ 35 nm implanted layer. The improvement of surface properties could also be confirmed by the nanoindentation technique, with values of hardness increasing for both processes. AFM (Atomic Force Microscopy) characterization showed that the single step PIII process presented greater efficiency than the duplex process (PIII + PN), probably due to the sputtering occurring during the second step (PN) removing partially the implanted layer of first step (PIII).
Characterization of Ti-6A1-4V modified by nitrogen plasma immersion ion implantation
Surface and Coatings Technology, 1997
Ti-6A1-4V alloy is commonly used in biomedical or aerospace applications, due to its excellent combination of chemical and mechanical properties, such as bioinertness, corrosion resistance or nigh strength to weight ratio. The use of surface treatments or coatings has widened the application possibilities of this alloy. The often observed poor tribological performance can be overcome by the correct choice of surface engineering methods. Ion implantation is a candidate among the different available processes and excellent results have been obtained in biomedical applications. However, when complex geometries are involved, it can be a difficult and less economically effective treatment. Plasma immersion ion implantation (PIII) offers the possibility of performing three-dimensional ion beam treatments, reducing the need for manipulation under vacuum to obtain a uniform treatment of geometrically complex parts.
Journal of Fusion Energy
In the present study the effect of nitrogen ion implantation on the structure of titanium surface and corrosion resistance have been investigated. In this experiment 30 keV nitrogen ion beam of 1 × 1018 to 5 × 1018 ions/cm2 fluence was used. Crystalline structure of the different samples was studied by X-ray diffraction analysis. The roughness variations before and after implantation were observed by atomic force microscopy. The corrosion test was used to compare the corrosion resistance of titanium before and after ion implantation. The surface morphology of the samples after corrosion test was investigated by scanning electron microscopy. The results showed that nitrogen ion implantation has a substantial effect on the improvement of titanium resistance against corrosion.
Nitrogen ion implantation and in vitro corrosion behavior of as-cast Ti–6Al–7Nb alloy
Corrosion Science, 2002
In the present investigation, surface modification of Ti-6Al-7Nb alloy with nitrogen ions is considered as a method to improve its performance with respect to corrosion. Nitrogen ion was implanted on Ti-6Al-7Nb alloy at an energy of 70 and 100 keV using a 150 keV accelerator at different doses between 1 Â 10 16 and 3 Â 10 17 ions/cm 2. Gracing incidence X-ray diffraction was employed on the implanted specimens to understand the phases formed with increasing doses. The implanted samples were subjected to electrochemical study in Ringer's solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The OCP of the implanted specimens were found to shift in the noble direction in comparison with unimplanted specimen. The passive current density and area of the repassivation loop were found to decrease as the dose values increased. The electrochemical impedance spectroscopic results indicate that the polarization resistance was higher for the dose of 2:5 Â 10 17 ions/cm 2 implanted at both energy of 70 and 100 keV. Nitrogen ion implantation enhanced the passivability and reduces the corrosion kinetics of the alloy surface with increasing tendency for repassivation. Nature of the surface and reason for the variation and improvement in corrosion resistance are discussed in detail.
Surface and Coatings Technology, 2016
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 × 10 +18 Ion cm −2 ) at room temperature (~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 α to β-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 K 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.
Corrosion Science, 2003
The aim of this paper is to study the effect of N þ ion implantation on corrosion and phase formation on the implanted surfaces of Ti-6Al-4V and Ti-6Al-7Nb alloys. Nitrogen ion was implanted on Ti-6Al-4V and Ti-6Al-7Nb alloys at an energy of 70 and 100 keV, respectively using a 150 keV accelerator at different doses ranging from 5 Â 10 15 to 2.5 Â 10 17 ions/cm 2. Electrochemical studies have been carried out in RingerÕs solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The implanted surfaces of such modified doses were electrochemically passivated at 1.0 V for an hour. Secondary ion mass spectroscopy was used to study and characterize titanium oxide and titanium nitride layers produced on implanted surface and to correlate them with the corrosion resistance. The nature of the passive film of the implanted-passivated specimen was compared with the unimplanted-passivated as well as as-implanted specimens.