Browsing by Author "Abad, M. D."
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Item Influence of carbon chemical bonding on the tribological behavior of sputtered nanocomposite TiBC/a-C coatings(2010-07-30) Abad, M. D.; Sánchez-López, J. C.; Brizuela, M.; García-Luis, A.; Shtansky, D. V.; INGENIERÍA DE SUPERFICIES; TECNOLOGÍAS DE HIDRÓGENOThe tribological performance of nanocomposite coatings containing Ti-B-C phases and amorphous carbon (a-C) are studied. The coatings are deposited by a sputtering process from a sintered TiB2:TiC target and graphite, using pulsed direct current and radio frequency sources. By varying the sputtering power ratio, the amorphous carbon content of the coatings can be tuned, as observed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The crystalline component consists of very disordered crystals with a mixture of TiB2/TiC or TiBxCy phases. A slight increase in crystalline order is detected with the incorporation of carbon in the coatings that is attributed to the formation of a ternary TiB xCy phase. An estimation of the carbon present in the form of carbide (TiBxCy or TiC) and amorphous (a-C) is performed using fitting analysis of the C 1s XPS peak. The film hardness (22 to 31 GPa) correlates with the fraction of the TiBxCy phase that exists in the coatings. The tribological properties were measured by a pin-on-disk tribometer in ambient conditions, using 6 mm tungsten carbide balls at 1 N. The friction coefficients and the wear rates show similar behavior, exhibiting an optimum when the fraction of C atoms in the amorphous phase is near 50%. This composition enables significant improvement of the friction coefficients and wear rates (μ ∼ 0.1; k < 1 × 10 -6 mm3/Nm), while maintaining a good value of hardness (24.6 GPa). Establishing the correlation between the lubricant properties and the fraction of a-C is very useful for purposes of tailoring the protective character of these nanocomposite coatings to engineering applications.Item Phase composition and tribomechanical properties of Ti-B-C nanocomposite coatings prepared by magnetron sputtering(2012-09-19) Sánchez-López, J. C.; Abad, M. D.; Justo, A.; Gago, R.; Endrino, J. L.; García-Luis, A.; Brizuela, M.; TECNOLOGÍAS DE HIDRÓGENO; INGENIERÍA DE SUPERFICIESProtective nanocomposite coatings based on hard ceramic phases (TiC, TiB 2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, TiBC nanocomposite coatings were prepared by co-sputtering of graphite and TiB 2 targets. Varying the discharge power ratio applied to the graphite and TiB 2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and x-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB 2-like structure to a distorted TiB xC y ternary compound with increasing C concentration. X-ray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiB xC y phase. A fitting analysis of the C 1s XPS peak allowed us to evaluate the relative amount of a-C and TiB xC y components. A drastic change in hardness (from 52 to 13GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB 2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45%. Raman observation of the wear tracks determined the presence of disordered sp 2-bonded carbon phase associated with the diminution of the friction level.