CARACTERIZACIÓN DE RECUBRIMIENTOS DE TiN MEDIANTE PULVERIZACIÓN CATÓDICA CON MAGNETRON (CHARACTERIZATION OF TiN COATINGS BY MAGNETRON SPUTTERING)

Resumen Los recubrimientos cerámicos de TiN por su dureza y resistencia al desgaste, son una opción viable para aumentar la vida útil de herramientas de corte y de partes mecánicas que son expuestos a una exigencia mayor que las superficies de aceros o materiales metálicos no pueden competir. Existen una diversidad de métodos para realizar recubrimientos cerámicos siendo identificados como parte de las técnicas los depósitos físicos por vapor (PVD), las cuales muestran altos valores de dureza y superficies lisas, características que en aplicaciones que requieran resistencia al desgaste es deseable; en específico en este trabajo enfocado en la técnica de pulverización catódica por magnetrón. El presente trabajo se enfoca en el depósito de nitruro de titanio (TiN) utilizando diferente relación de flujo gaseoso Ar: N2, para identificar como el cambio de concentración de N2 afecta en la tasa de depósito, composición química y estructura en cada uno de los recubrimientos de TiN. Los resultados muestran como la tasa de depósito es afectada por la cantidad de flujo N2 definido en cada experimento, ocasionando que disminuya; se observa una composición química del recubrimiento próxima a la estequiometria TiN, y una orientación preferencial presente en las películas sobre la dirección (111). Palabras Clave: Nitruro de Titanio, pulverización catódica asistida por magnetrón, tasa de depósito. Abstract TiN ceramic coatings has a high hardness and wear resistance that make them a suitable option to increase the life-time of tools and mechanical parts that conventional steels or metallic materials cannot are support. There are a variety of methods for making ceramic coatings, physical vapor deposits (PVD) being identified as part of the techniques, which show high values of hardness and smooth surfaces, characteristics that in applications requiring resistance to wear are desirable; specifically in this work focused on the magnetron sputtering technique. The present work concentrates on the titanium nitride (TiN) deposit using different gas flow rate Ar: N2, to identify how the change in N2 concentration affects the deposit rate, chemical composition, and structure in each of TiN coatings. The results show how the deposit rate is affected by the amount of N2 flow defined in each experiment, causing it to decrease; a chemical composition of the coating close to the TiN stoichiometry is observed, and a preferential orientation present in the films on the direction (111). Keywords: Titanium Nitride, magnetron sputtering, deposition rate, coating chemical composition

Tribological Response of δ-Bi2O3 Coatings Deposited by RF Magnetron Sputtering

Bismuth oxide (Bi2O3) coatings and composite coatings containing this oxide have been studied due to their potential applications in gas sensing, optoelectronics, photocatalysis, and even tribology. Two parametric models based on chemical features have been proposed with the aim of predicting the lubricity response of oxides. However, such models predict contradictory values of the coefficient of friction (COF) for Bi2O3. In this study, we deposited Bi2O3 coatings, via magnetron sputtering, on AISI D2 steel substrates to evaluate the tribological responses of the coatings and determine which parametric model describes them better. Experimentally, only coatings presenting the cubic defective fluorite-like δ-Bi2O3 phase could be evaluated. We performed pin-on-disk tests at room temperature and progressively increasing temperatures up to 300 °C using alumina and steel counter-bodies. Low wear and COFs (0.05 to 0.15) indicated that the δ-phase behaves as a lubricious solid, favoring the validity of one of the models. An alternative explanation is proposed for the low COF of the defective fluorite-like structure since it is well known that it contains 25% of anionic vacancies that can be ordered to form low shear-strength planes, similar to the Magnéli phases. Two challenges for future potential applications were observed: one was the low adhesion strength to the substrate, and the other was the thermal stability of this phase.This research was funded by PAPIIT-UNAM Project IV200222.Peer reviewe

Synthesis and properties of Bi5Nb3O15 thin films prepared by dual co-sputtering

International audienceBismuth-based oxides have gained attention because of their particular electronic configuration that enhances the mobility of photogenerated carriers. In this work, we focused on the synthesis, and the evaluation of the physical and photocatalytic properties of Bi5Nb3O15 films. Bismuth niobate films were deposited by dual magnetron co-sputtering, starting from Bi2O3 and Nb independently driven targets. Although the substrates were heated at 150 degrees C during the deposition, the films were amorphous; therefore, they were annealed at 600 degrees C in air for 2 h to obtain the nanocrystalline Bi5Nb3O15 orthorhombic phase. The Bi5Nb3O15 compound is an interesting material for applications in microelectronics due to its high-k dielectric value at the radiofrequency range; another possible and reported application is as photocatalyst for degradation of organic pollutants and water splitting processes. The films structure was confirmed by X-ray diffraction (theta-2 theta and in-plane modes). The Raman and infrared spectra were measured and compared with calculated vibrational modes since they have not been reported in the past. The optical properties (refractive index, extinction and absorption coefficients) of the Bi5Nb3O15 films were estimated using UV-VIS reflectance and transmittance spectroscopy. The optical band gap was estimated assuming an indirect fundamental inter-band transition at 3.25 eV. The prospective to use the Bi5Nb3O15 films as a photocatalyst was evaluated through the measurement of the photo-discoloration of indigo carmine (IC) dye solutions (5 ppm) under UV light irradiation at three pHs: 3.5, 7 and 11. The results showed a decrease in the absorbance spectrum of the IC solution as a function of irradiation time only at acidic pH where almost 100% of degradation was achieved at 270 min; this behavior is probably due to the increment of the adsorption of IC molecules on the positively charged surface. A similar response was observed after 5 cycles without any structural change of the films. (C) 2016 Elsevier B.V. All rights reserved

Degradation Behavior and Mechanical Integrity of a Mg-0.7Zn-0.6Ca (wt.%) Alloy: Effect of Grain Sizes and Crystallographic Texture

The microstructural characteristics of biodegradable Mg alloys determine their performance and appropriateness for orthopedic fixation applications. In this work, the effect of the annealing treatment of a Mg-0.7Zn-0.6Ca (ZX11) alloy on the mechanical integrity, corrosive behavior, and biocompatibility-osteoinduction was studied considering two annealing temperatures, 350 and 450 °C. The microstructure showed a recrystallized structure, with a lower number of precipitates, grain size, and stronger basal texture for the ZX11-350 condition than the ZX11-450. The characteristics mentioned above induce a higher long-term degradation rate for the ZX11-450 than the ZX11-350 on days 7th and 15th of immersion. In consequence, the mechanical integrity changes within this period. The increased degradation rate of the ZX11-450 condition reduces 40% the elongation at failure, in contrast with the 16% reduction for the ZX11-350 condition. After that period, the mechanical integrity remained unchanged. No cytotoxic effects were observed for both treatments and significant differentiation of mesenchymal stem cells into the osteoblast phenotype was observed