Browsing by Author "Garcia, 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 Detection of stator short circuits in PMSM by mean of joint time-frequency analysis(2007) Rosero, J.; Cusido, J.; Garcia, A.; Romeral, L.; Ortega, J. A.; FACTORYThis paper presents and analyzes short circuit failures for Permanent Magnet Synchronous Motor (PMSM). The study includes speed transients in realistic experimental conditions. The stator current is analyzed by means of time-frequency spectral distribution (SP), Wigner Ville distribution (WVD) and Analytical Wavelet Transform (AWT); also, the rms value of the local maximum for this distribution is calculated as indicated by Ridge-AWT algorithm. Experimental laboratory results validate the analysis and demonstrate that the time- frequency analysis can be applied to detect and identify short circuit failures in synchronous machines*.Item Micromechanical properties of diamond films deposited by microwave-plasma-enhanced chemical vapour deposition(1993-04-13) Garcia, A.; Flaño, N.; Viviente, J. L.; Onate, J. I.; Gomez-Aleixandre, C.; Sanchez-Garrido, O.; Centros PRE-FUSION TECNALIA - (FORMER); TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOS; Tecnalia Research & InnovationThis paper reports on the study of mechanical properties of diamond films produced by microwave plasma chemical vapour deposition on silicon under different deposition conditions. The quality of films has been examined by scanning electron microscopy, Raman spectroscopy and Auger electron spectroscopy. Raman and Auger electron spectra show significant differences between the sp3 and sp2 bonding characters depending on the methane concentrations used in the deposition of diamond films. The microstructure of these films has a significant influence on the microhardness and elastic properties measured by a dynamic microindentation technique in a load range 0.4-10 mN. Changes in film quality have shown variations in these values, leading to a relationship between the microstructure and mechanical properties of these diamond films. The best results have been obtained for diamond films deposited at CH4 concentrations in H2 of less than 0.5 vol.%, reaching hardness values of up to 42 GPa and percentages of elastic recovery of up to 84.5%.Item Tribological effects of yttrium and nitrogen ion implantation on a precipitation hardening stainless steel(1994-08) Alonso, F.; Arizaga, A.; Garcia, A.; Oñate, J. I.; Centros PRE-FUSION TECNALIA - (FORMER); Tecnalia Research & InnovationYttrium, nitrogen and combined yttrium and nitrogen implantations have been carried out on an ASTM A286 precipitation hardening iron base alloy to evaluate the benefits in their tribological behaviour. Microindentation tests have shown a significant 20%-60% increment in hardness on the nitrogen implanted material, with a limited improvement in elastic recovery of the indentation. An abrasive test on the same material has also produced a 50% reduction in scratch depth. Y+ and Y+ + N+ implantations also hardened the material but to a lesser extent. Reciprocating ball on disk friction and wear testing at 400 °C resulted in very severe damage in all cases. X-ray photoelectron spectroscopy analyses combined with Ar sputtering have disclosed that nitrogen is mainly in a nitrided form, yttrium remains oxidized at the surface, below which there is an apparent increase in the metallic bond.Item Wear behaviour of copper matrix composites(1997) Coupard, D.; Castro, M. C.; Coleto, J.; Garcia, A.; Goni, J.; Palacios, J. K.; Mercado; Centros PRE-FUSION TECNALIA - (FORMER)Wear and friction behavior of CuSnl2 bronze and CuSnl2 bronze/graphite-alumina composites have been investigated. The CuSnl2 composite shows excellent wear resistance and a lower coefficient of friction with respect to its matrix alloy. The tribological properties of the composite are mainly attributed to the thin layer of graphite at the surface of the wear track impeding the metal-to-metal contact. Thus, the coefficient of friction of the CuSnl2 composite is three times lower than that of the CuSnl2 bronze and the composite wear loss could not be detected after a 30 minutes wear test under a load and velocity of respectively 30 Kgs and 166 mm/s.Item Wear reduction effect on ultra-high-molecular-weight polyethylene by application of hard coatings and ion implantation on cobalt chromium alloy, as measured in a knee wear simulation machine(2001-07) Onate, J.I.; Comin, M.; Braceras, I.; García-Luis, A.; Viviente, J.L.; Brizuela, Marta; Garagorri, N.; Peris, J.L.; Alava, J.I.; Oate, J. I.; Garcia, A.; Tecnalia Research & Innovation; INGENIERÍA DE SUPERFICIES; TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOSThe most important factor affecting performance and longevity of hip joint and knee implants is the wear rate of the ultra-high-molecular-weight polyethylene (UHMWPE) component. UHMWPE wear debris has been linked to complications including tissue inflammation, bone loss (osteolysis) and implant loosening. Reduction of debris has been addressed by investigating new polyethylene formulations, manufacturing and finishing processes, including surface treatments and coatings both on plastic and metallic components. There have been many studies on the effect of surface treatments and hard coatings on cobalt chromium and titanium alloys for prosthetic applications. However, most of them have used laboratory tribo-testers without much correlation to articulating movements in human joints. In this work, hard coatings (TiN and DLC) and surface treatments (nitrogen ion implantation) have been investigated as potential candidates to reduce wear of UHMWPE, when applied on the counter face cobalt chromium alloy. Also the effect of applying nitrogen ion implantation on the UHMWPE surface itself has been investigated. To evaluate wear performance a special knee wear simulator has been used with a combined rolling-sliding movement that corresponds to the most unfavourable situation in the knee. As testing materials, conventional coated and uncoated Co–Cr as well as Al2O3 femoral heads were used against UHMWPE plates to obtain comparative data. Testing was carried out at 50 MPa using distilled water at 37±2°C as a lubricant. Wear measurements on UHMWPE were made following ASTM F732 standard by weight loss measurements and also by laser profilometry. The results, up to 5 million wear cycles that represent approximately 3 years of implant life, clearly have demonstrated the beneficial effects of diamond-like carbon (DLC) and ion implantation (both on Co–Cr and UHMWPE) in reducing wear of UHMWPE. Similar values were also obtained for Al2O3 ceramic material. A wear reduction up to approximately five times was obtained by the former materials, in comparison with the uncoated control specimen. However, the ion plated TiN coating increased significantly wear on the UHMWPE. Transference of UHMWPE to the ball was very evident with the uncoated control and TiN coated Co–Cr, as observed by SEM, but with DLC and the ceramic material this occurred to a much lesser extent. Some micro-delamination at the worn surface of the UHMWPE was observed when wearing against uncoated Co–Cr, but was not clear in the rest options. Ion implantation and DLC can thus be two good candidate treatments to reduce wear of UHMWPE in cobalt chromium knee and hip joint implants in substitution of a more expensive ceramic material. This DLC has passed all biocompatible tests in accordance with FDA regulations and ISO 10993 standards for implantable devices. An example of a uniformly DLC coated femoral head and knee implant is shown.