Browsing by Author "Loinaz, A."
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Item Carbon layers formed on steel and Ti alloys after ion implantation of C+ at very high doses(1999) Viviente, J. L.; Garcia, A.; Loinaz, A.; Alonso, F.; Oñate, J. I.; TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOS; Centros PRE-FUSION TECNALIA - (FORMER); Tecnalia Research & InnovationIon implantation is a useful technique to tailor surface properties of steel and Ti alloys. In particular, very high dose C+ implantation (in the range of 1018 ions cm-2) offers the possibility of forming carbon layers without a sharp interface with the substrate material. In this study, ion implantation of carbon doses up to 8 × 1018 ions cm-2 has been performed on 440C martensitic stainless steel and Ti6A14V substrates under similar conditions and tribological and surface analysis results have been compared. Surface hardening occurred for all ion implantation conditions up to doses of 1018 ions cm-2 [1-3]. Higher doses resulted in a different behaviour for both materials. The stainless steel showed a softening while a twofold hardness increase was maintained in the Ti alloy. Nevertheless, at the higher implanted dose a decrease in hardness was also observed in the Ti alloy. Small area XPS analyses were performed to evaluate the chemical states after ion implantation and establish a relationship with the observed surface hardening. Depth profile XPS analyses showed that for a dose of 4 × 1018 ions cm-2 a carbon layer (with concentration over 85% at. C) was formed in the near surface region for both materials.Item Characterization of Ti-6Al-4V modified by nitrogen plasma immersion ion implantation(1997-09) Alonso, F.; Rinner, M.; Loinaz, A.; Oñate, J. I.; Ensinger, W.; Rauschenbach, B.; Centros PRE-FUSION TECNALIA - (FORMER); Tecnalia Research & InnovationT1-6Al-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 high 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. In this work, PIII was used to implant nitrogen in the Ti-6Al-4V alloy. The nitrogen plasma was generated with a 2.45 GHz microwave excitation, and a pulsed bias voltage of 45 kV with pulse repetition rates of 50 and 400 Hz were applied. Nitrogen retained doses were evaluated by means of Rutherford backscattering spectroscopy (RBS). Pin-on-disc wear and friction tests were performed on the implanted samples. An ultra high molecular weight polyethylene pin was used as the counterface material to partially simulate the conditions encountered in biomedical applications. A reasonable improvement in load bearing capacity with respect to the unimplanted alloy was observed after these tribological tests. However, no hardening could be measured after ion implantation. The worn surfaces were observed by scanning electron microscopy and optical profilometry after the tests and the type of wear mechanism was studied. The effect of the implantation was to increase the load at which breakthrough occurred on the protective surface layer.Item Effects of plasma immersion ion implantation of oxygen on mechanical properties and microstructure of Ti6A14V(1998-05) Loinaz, A.; Rinner, M.; Alonso, F.; Oñate, J. I.; Ensinger, W.; Centros PRE-FUSION TECNALIA - (FORMER); Tecnalia Research & InnovationPlasma immersion ion implantation (PIII) is a surface treatment with increasing interest, as it offers the possibility of performing three-dimensional ion beam treatments, reducing the need for manipulation under vacuum to obtain a uniform treatment in geometrically complex parts. In this work the PIII process has been used to perform surface treatment on Ti6A14V alloy. This Ti alloy is commonly used in aerospace and biomedical applications, due to its good combination of mechanical and chemical properties, such as strength to weight ratio, corrosion resistance or bioinertness. However, due to its poor tribological properties, the use of surface treatments to improve wear resistance or decrease friction coefficient is often recommended. PIII has been used to implant the surface of Ti6A14V alloy with oxygen ions. The oxygen plasma was generated by electron cyclotron resonance microwave excitation, working at two different pressures. At the lower pressure plasma density was increased by means of an external ring magnet. High voltage pulses of -40 kV, at of 400 and 600 Hz pulse repetition rates, were applied. Elastic recoil detection (ERD) analysis showed retained doses in the range of 3 × 1017 to 1 × 1018 O atoms cm-2, with oxygen concentration values ca 65% in the near surface region. Surface mechanical properties such as hardness, wear and friction have been evaluated. Microindentation tests showed an increase of up to 100% in the surface hardness of the ion implanted samples compared to the non implanted material. Dry pin-on-disk tests with spherical ended UHMWPE pins showed a very significant increase in wear resistance in oxygen implanted Ti6A14V samples. Scanning electron microscopy and optical profilometry showed an important roughening of the Ti alloy surface after PIII treatment under selected conditions.Item Growth of carbon layers on Ti-6Al-4V alloy by very high dose carbon implantation(1997-12) García, A.; Viviente, J. L.; Alonso, F.; Loinaz, A.; Oñate, J. I.; TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOS; Centros PRE-FUSION TECNALIA - (FORMER); Tecnalia Research & InnovationIon implantation is a useful technique to tailor the surface properties of Ti-6Al-4V alloys. In particular, very high dose C+ implantation (in the range of 1018 ions cm-2) offers the possibility of forming carbon layers without a sharp interface with the substrate material. In this study, ion implantation treatments have been performed on Ti-6Al-4V with C+ doses up to 4 × 1018 ions cm-2. XPS analyses have been carried out to evaluate the chemical states after ion implantation. A change in C 1s binding energies has been observed depending on the carbon concentration in the implanted layer. At relatively low or medium concentrations (about 41 at.% C) mainly carbidic bonds were present, but when the concentration increased up to 88 at.%, the binding peak shifted to values that correspond to C-C bonds. Dynamic microindentation techniques, used to evaluate the hardness of the implanted material, have shown a significant change in relative hardness as a function of C+ dose, owing to the formation of a carbon layer in the titanium alloy surface. A two-fold increase in the hardness ratio and elastic recovery values is observed for the highest implanted dose.