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Abstract: CoCr alloys are widely used in some specific hip and knee prosthesis. In particular, they are used in advanced metal on metal (MoM) prostheses. However, while these new implants have an intermediate wear rate between low wear ceramic–metal and high wear polymer–metal prostheses, a high risk of metalosis produced by wear debris, originated in the metal–metal sliding contact, is still present. Oxygen plasma immersion ion implantation (PI3) provides a practical method to improve wear resistance of CoCr alloys, thus reducing the amount of wear particles. This paper describes the tribological and wear resistance improvements of CoCr alloy implanted by PI3. Friction and wear tests were performed to investigate the modifications obtained by oxygen implantation. Glow Discharge Optical Emission Spectrometry (GD-OES) analysis was employed to evaluate the oxide layer thickness and compositional changes of the metallic alloying elements produced by the oxygen treatment. Moreover, SEM analysis was carried out for detecting wear particles after ball on disk tests in a biological solution simulating the human body fluid. The reported results indicate that PI3 improves the wear resistance of CoCr alloy to be used in human body implants. [Copyright &y& Elsevier]

In this contribution, we report on the structural and the tribological characterisation of low-energy nitrogen-ion-implanted Vanadium Titanium (V5Ti) alloys as a function of the annealing temperature during the bombardment process. The surface of the alloys was bombarded with N2+ ions accelerated at 1.2 keV in a vacuum chamber equipped with a Kaufman-type ion source. The temperature during the low-energy ion implantation were 480, 500, and 575 °C. In this temperature range, the penetration depth reached by the implanted ions is not only exclusively ballistic (i.e., kinetic energy dependent), but diffusion effects also play a decisive role.The structural changes can be drawn as the formation of a nitrogen diffusion layer containing a blend of pristine bcc V5Ti and a solid nitrogen solution having an expanded bcc phase. It has been found that the temperature favours the increase of both, the thickness of the diffusion layer and the relative nitrogen content in the solid solution.We have investigated the microhardness, friction and wear coefficients of the implanted V5Ti surfaces as a function of the annealing temperature. The reported results indicate that both hardness and wear resistance against mechanical abrasion increase as the temperature during the bombardment increases. This increment of the hardness and wear resistance could be directly correlated to the amount of the expanded phase exhibited by the V5Ti surfaces, as observed by X-ray diffraction. The hardness and wear resistance modification upon annealing temperature are discussed in terms of the plastic deformation undergone by the expanded bcc phase to release the accumulated lattice stresses. [Copyright &y& Elsevier]

This article reports the study of the changes in the surface properties of metals of group VIa after their implantation with atomic nitrogen. Doses of 1E17 N+, 5E17 N+ and 1E18 N+ ions/cm2 were implanted on polished samples of chromium, molybdenum and tungsten, in order to investigate the tribological effects due to implantation. This work is the continuation of the study carried out on groups IVb and Va, where the effects of nitrogen implantation were also evaluated. Microindentation hardness at low loads, friction and wear tests have been carried out on the different materials and doses in an attempt to relate surface modifications with the implanted dose. Microindentation hardness tests at low loads showed increases of at least a factor 2 in all the cases. Friction tests against Co–WC were performed, finding the higher friction reductions for molybdenum. AES and GDS profiles have also been performed to determine the nitrogen distribution after the implantation experiments. [Copyright &y& Elsevier]

The formation of expanded austenite in austenitic stainless steel and CoCr alloys is a well established fact while the underlying mechanisms are still contended. When inserting nitrogen by plasma immersion ion implantation (PIII), additional auxiliary heating allows continuous increase of the average current density by either incrementing the voltage or the pulse repetition frequency. For the nitrogen content and layer thickness, monotonously increasing values are observed, indicating an additive process for the nitrogen uptake from low energy plasma ions adsorbing on the surface and high energy ions implanted below the surface. A supply limited diffusion is apparently occurring throughout the whole ion flux range as no saturation is observed at the processing temperature of 400 °C. A much stronger influence of the ion fluence on the surface concentration in stainless steel than in CoCr alloys is observed. On the other hand, while the lattice expansion scales directly with the surface nitrogen content, a non-monotonous influence of the ion flux on the detailed peak shape, respective stress and stress gradients is observed. [ABSTRACT FROM AUTHOR]

Nitriding of biomedical CoCr alloys at elevated temperatures leads to a marked increase in the hardness and wear resistance. However, a compromised corrosion resistance is encountered even at relatively low temperatures, not correlated with the appearance of CrN in the XRD spectra. A duplex treatment of initial nitrogen and subsequent oxygen PIII at 350 °C was already shown to partially reduce the corrosion current. Here, it is investigated whether restoring the oxide passivation layer by PIII is necessary, a simple annealing is sufficient or an intermediate processing is more suitable. GDOES, XRD, XPS and corrosion investigations in bovine serum are performed to obtain information on the underlying mechanisms of the improved corrosion resistance. It is shown that post-oxidation by PIII leads to a more favourable corrosion protection with lower corrosion current and more positive corrosion potential compared to thermal oxidation or plasma oxidation. As the XPS and GDOES data show no differences, the cause of this behaviour should be correlated with the microstructure of the oxide. [ABSTRACT FROM AUTHOR]

Abstract: The formation of expanded austenite in austenitic stainless steel and CoCr alloys is a well established fact while the underlying mechanisms are still contended. When inserting nitrogen by plasma immersion ion implantation (PIII), additional auxiliary heating allows continuous increase of the average current density by either incrementing the voltage or the pulse repetition frequency. For the nitrogen content and layer thickness, monotonously increasing values are observed, indicating an additive process for the nitrogen uptake from low energy plasma ions adsorbing on the surface and high energy ions implanted below the surface. A supply limited diffusion is apparently occurring throughout the whole ion flux range as no saturation is observed at the processing temperature of 400°C. A much stronger influence of the ion fluence on the surface concentration in stainless steel than in CoCr alloys is observed. On the other hand, while the lattice expansion scales directly with the surface nitrogen content, a non-monotonous influence of the ion flux on the detailed peak shape, respective stress and stress gradients is observed. [Copyright &y& Elsevier]

Abstract: In this work, dual implantation of Cr+ and N2 + ions on electroplated Ni substrates have been investigated for N2 + implantation energies of 140keV, 100keV and 60keV. The implanted specimens have been analyzed by glow discharge optical emission spectroscopy, X-ray diffraction, nano-indentation, coefficient of friction, nano-wear and potentiodynamic corrosion curves. The properties of the dual implanted samples have been compared to Cr+ or N2 + implanted specimens. The microstructural and mechanical properties of the Ni plates depend on the penetration ranges of the Cr and N atomic profiles obtained after the implantation process. The increase of hardness reduced the coefficient of friction of the samples and the wear rates. Preferential formation of Cr–N over Ni–N compounds has been observed when the Cr and N atomic profiles coexist within the Ni matrix. The potentiodynamic corrosion curves in acidic solutions revealed that the presence of Me–N species is detrimental for the chemical stability of the plates. Both nano-wear and corrosion properties are optimized when a Ni–N sublayer is formed underneath a top Cr–Ni implanted film. This is achieved by tuning the implantation energies of Cr+ and N2 + ions at 140keV. This bilayer structure could be a suitable treatment for micro-embossing dies for plastic texturing processes. [Copyright &y& Elsevier]

Abstract: In this work, a successful sequential co-implantation treatment of Cr+ and N2 + ions into electrodeposited nickel plates is presented. The goal of this treatment is the simultaneous enhancement of the wear resistance, mechanical stability and corrosion-protection properties of the Ni surfaces. The ion-implanted surfaces have been characterized by glow-discharge optical-emission spectroscopy, X-ray diffraction, nano-hardness, roughness, nano-wear and potentio-dynamic corrosion tests. It has been observed that the implantation of Cr+ or N2 + alone is not sufficient to achieve simultaneously the enhancement of both the wear-resistance and the corrosion-protection properties. Conversely, the sequential implantation of Cr+ and N2 + at 140keV and fluencies of 3×1017 and 1.5×1017 ions/cm2 respectively, permits the formation of a functional surface capable of reducing both the corrosion rate and the wear rates, with respect to those exhibited by the un-implanted Ni surfaces. This treatment can be used to protect the surfaces of micro-embossing/stamping dies based on electroformed Nickel, as an alternative to other coating strategies. Furthermore, the ion implantation assures the non-modification of the net-shape and surface finish of these types of dies, which is of crucial importance when they are used for high-precision micro-texturing/imprinting applications. [Copyright &y& Elsevier]