Publications

Publications

Nanoscale colour control: W-O graded coatings deposited by magnetron sputtering

  • Authors: prof. Ing. Tomáš Polcar, Ph.D., Kubart, T., Malainho, E., Vasilevskiy, M., Parreira, N.M.G., Cavaleiro, A.
  • Publication: Nanotechnology. 2008, 19(39), 395202-395206. ISSN 0957-4484.
  • Year: 2008
  • DOI: 10.1088/0957-4484/19/39/395202
  • Link: https://doi.org/10.1088/0957-4484/19/39/395202
  • Department: Department of Control Engineering
  • Annotation:
    A new design of decorative tungsten oxide coatings is presented. The coatings were deposited with a graded refractive index by magnetron sputtering from a tungsten target and pulsing the reactive gas. The controlled injection of the reactive gas can produce a concentration profile gradient from pure tungsten to tungsten trioxide, determining the final apparent colour of the coating. A dynamic sputtering model was built to simulate the growth of the coating during the reactive gas pulsing which was validated by direct measurement of the gradient of the oxygen content in the deposited coatings. Finally, these results were used for an optical model allowing the optical properties of the deposited tungsten oxide layer to be described, again validated by experimental analysis.

A simple model for the deposition of W-O coatings by reactive gas pulsing process

  • Authors: Parreira, N.M.G., prof. Ing. Tomáš Polcar, Ph.D., Carvalho, N.J.M., Cavaleiro, A.
  • Publication: The European Physical Journal Applied Physics. 2008, 43(3), 321-325. ISSN 1286-0042.
  • Year: 2008
  • DOI: 10.1051/epjap:2008068
  • Link: https://doi.org/10.1051/epjap:2008068
  • Department: Department of Control Engineering
  • Annotation:
    The conventional and RGPP process parameters (target potential, total pressure and deposition rate) and the corresponding chemical composition were used to build a simple model predicting the deposition rate and the average chemical composition of the coatings deposited by RGPP as a function of the pulsing parameters. It was shown that the measured total pressure could be used to calculate the deposition rate and the chemical composition of the RGPP coatings with reasonable precision.

In Situ Structural Evolution of Arc-Deposited Cr-Based Coatings

  • Authors: Neves, A.M., Severo, V., Cvrček, L., prof. Ing. Tomáš Polcar, Ph.D., Louro, C., Cavaleiro, A.
  • Publication: Surface and Coatings Technology. 2008, 202(22-23), 5550-5555. ISSN 0257-8972.
  • Year: 2008
  • DOI: 10.1016/j.surfcoat.2008.06.102
  • Link: https://doi.org/10.1016/j.surfcoat.2008.06.102
  • Department: Department of Control Engineering
  • Annotation:
    Cr-based coatings were prepared by cathode arc evaporation technology using N2 and C2H2 as reactive gases. Three compositions were investigated, Cr60N40, Cr41N27C32 and Cr67C33. The present investigation is centred on the structural stability via coatings tempering up to 1000°C, by in situ X-ray diffraction in inert atmosphere.

Structure and Tribology of Biocompatible Ti-C:H Coatings

  • Authors: Ing. Tomáš Vítů, Ph.D., prof. Ing. Tomáš Polcar, Ph.D., Cvrček, L., Novák, R., Macák, J., Vyskočil, J., Cavaleiro, A.
  • Publication: Proceedings of Sixth Asian-European International Conference on Plasma Surface Engineering (AEPSE 2007). Nagasaki: Asian Joint Committee on Plasma Surface Engineering (AJC/PSE), 2007. pp. 361.
  • Year: 2007
  • Department: Department of Control Engineering
  • Annotation:
    Ti-C:H coatings with different carbon content for biomedical applications were deposited by PECVD. Ti was varied by magnetron sputtering a Ti-target with different power in a dc discharge regime having Ar in the atmosphere. The tribological properties were studied using a pin-on-disc CSM Tribometer in order to ensure stable tribological properties of the whole Ti-C:H/DLC system for any case of top layer failure. The sliding tests were carried out at room temperature in room environment with relative air humidity 40+-5%, in 0.9% NaCl water solution (physiological solution, PS) and in 10% fetal bovine serum (FBS) dissolved in Ringer's saline solution using 440C steel balls with a diameter of 8 mm. The Ti-rich coatings exhibited poor wear resistance, while the best tribological properties were achieved for TiC/a-C:H coatings deposited with the highest C2H2 flows.

Mechanical and Tribological Properties of Sputtered Mo-Se-C Coatings

  • Authors: prof. Ing. Tomáš Polcar, Ph.D., Evaristo, M., Stueber, M., Cavaleiro, A.
  • Publication: ECOTRIB 2007. Ljubljana: Slovenian Society for Tribology, 2007. pp. 613-623. ISBN 978-961-90254-8-2.
  • Year: 2007
  • Department: Department of Control Engineering
  • Annotation:
    Mo Se C films were deposited by sputtering from a C target with pellets of MoSe2. Besides the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the tribological characterization. The C content varied from 29 to 68 at.% which led to a progressive increase of the Se/Mo ratio. As a typical trend, the hardness increases with increasing C content. The coatings were tested at room temperature with different air humidity levels and at temperatures up to 500 oC on a pin-on-disc tribometer. The friction coefficient of Mo-Se-C coatings increased with air humidity from ~0.04 to ~0.12, while it was as low as 0.02 at temperature range 100-250 oC. The coatings were very sensitive to the elevated temperature being worn out at 300 oC due to adhesion problems at coating - titanium interface.

Comparative study of the tribological behavior of self-lubricating W-S-C and Mo-Se-C sputtered coatings

  • DOI: 10.1016/j.wear.2008.04.011
  • Link: https://doi.org/10.1016/j.wear.2008.04.011
  • Department: Department of Control Engineering
  • Annotation:
    In this paper, the general comparison between W-S-C and Mo-Se-C coatings is presented. The main effort is pointed on the tribological behavior of both systems when tested by pin-on-disk against steel counterpart balls under different testing conditions: applied normal loads, temperatures and relative humidity of the atmospheres. Both coatings were deposited by co-sputtering from a C target with a varying number of TMD pellets which could lead to C contents in the films in the range from 30 up to 70 at.%. A Ti interlayer was interposed between the films and the substrates for improving the adhesion. Typically, W-S-C films are harder than Mo-Se-C films. From the tribological point of view, W-S-C films are more thermally stable than Mo-Se-C films although the friction coefficients of these last ones are lower when tested in humid containing atmospheres.

Synthesis and Structural Properties of Mo-Se-C Sputtered Coatings

  • Authors: prof. Ing. Tomáš Polcar, Ph.D., Evaristo, M., Stueber, M., Cavaleiro, A.
  • Publication: E-MRS Spring Meeting 2007 - Book of Abstracts. Strasbourg: E-MRS, 2007. pp. 150.
  • Year: 2007
  • Department: Department of Control Engineering
  • Annotation:
    Mo-Se-C coatings were prepared by non-reactive r.f. magnetron sputtering from carbon target with embedded MoSe2 pellets. The carbon content and Se/Mo ratio determined by electron probe microanalysis increased from 29 to 68 at.% and from 1.7 to 2.0, respectively, as a function of the decreasing number of pellets. The coating structure analyzed by X-Ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy showed that Mo-Se-C was a mixture of amorphous carbon and Mo-Se phases, since no traces of molybdenum carbides were observed. Linear increase of the hardness from 0.7 (29 at.% C) to 4.1 GPa (68 at.% C) showed a significant improvement compared to values typical for pure MoSe2 coating.

Structural and tribological characterization of tungsten nitride coatings at elevated temperature

  • DOI: 10.1016/j.wear.2007.10.011
  • Link: https://doi.org/10.1016/j.wear.2007.10.011
  • Department: Department of Control Engineering
  • Annotation:
    The structure, hardness, friction and wear of tungsten nitride coatings with nitrogen content in the range 30-58 at.% prepared by dc reactive magnetron sputtering were investigated. The tribological tests were performed on a pin-on-disc tribometer in terrestrial atmosphere with Al2O3 balls as sliding partner. The coating wear rate was negligible up to 200 °C exhibiting a decreasing tendency; however, the wear dramatically increased at higher temperatures. The coating peeled off after the test at 600 °C, which is connected with the oxidation of the coating.

Study of the Cathode Potential in a Sputtering Discharge by Pulsing the Reactive Gas: Case of a W Target in an Ar-O2 Atmosphere

  • Authors: Parreira, N.M.G., prof. Ing. Tomáš Polcar, Ph.D., Cavaleiro, A.
  • Publication: Plasma Processes and Polymers. 2007, 4(1), 62-68. ISSN 1612-8850.
  • Year: 2007
  • Department: Department of Control Engineering
  • Annotation:
    The process we used was d.c. magnetron sputtering, and we studied both the conventional process, using a constant flow of oxygen, and the process in which we pulsed the reactive gas. Square regulation signal with different pulsing periods (T) and oxygen injection time (ton) was used in the reactive gas pulsing (RGP), while the partial argon pressure was kept constant for all depositions.

Tribological Characterization of Tungsten Nitride Coatings Deposited by Reactive Magnetron Sputtering

  • Department: Department of Control Engineering
  • Annotation:
    The structure, hardness, friction and wear of tungsten nitrides prepared by d.c. reactive magnetron sputtering were investigated. The coatings were deposited with different nitrogen to argon ratios; the total pressure was kept constant. The tribological tests were performed on a pin-on-disc tribometer in terrestrial atmosphere with 100Cr6 steel, Al2O3 and Si3N4 balls as sliding counter-bodies. The wear tracks, the ball-wear scars and the wear debris were analysed by scanning electron microscopy in order to characterize the dominant wear mechanisms.

Responsible person Ing. Mgr. Radovan Suk