1,721,156 research outputs found
Current industrial practice critical issues in hard PVD and PA-CVD coatings
No full textIn this paper the authors address a few - amongst many others - critical issues in hard coatings. These issues are: (1) the development of standardisation techniques for quality assurance and how well laboratory tests can be used for supporting such techniques. As an example fretting wear testing is discussed. (2) The importance of developing dedicated coatings for dry machining and/or manufacturing under reduced cooling/lubrication. (3) The role of plasma diagnostics in the development of coatings. (4) The problem of process control in CVD diamond coating in relation to adhesion and film structure.This work is financially supported by the "Nationaal
Fonds voor Wetenschappelijk Onderzoek, Brussels"
under contract no. G.0014.96 and contract no.
G.4.0004.94. This paper presents research results of the
Belgian Programme on Interuniversity Attraction Poles
initiated by the Belgian State Prime Minister's Office
(Brussels), Science Policy Programming. Scientific
responsibility is assumed by the authors.
Thanks are due to Ing. M. Kerkhofs (WTCM-Surface
Treatment, Diepenbeek, Belgium) for providing the
results of the experiment on deep drawing of catalysts
shells, to dr. S. Kadlec and drs. S. Wouters for providing
the results of Figs. 4-6, to dra. K. Yandierendonck for
allowing to make use of the data of Figs. 7-11, to drs
Th. Vandevelde for providing the data of Fig. 14. Thanks
are also due to Prof. G. Knuyt for critical discussions
related to Fig. 12
A method for determination of the effective diffusion coefficient and sputtering rate during plasma diffusion treatment
No full textA method for determination of the effective diffusion coefficient and sputtering rate in plasma diffusion treatment of materials is presented. The method is based on a previously proposed plasma nitriding diffusion model, where the nitrided layer thickness as a Function of time is the main input data for determination of the nitrogen diffusion coefficient. The method is compared with the results of determination of diffusion coefficients in plasma nitrided austenitic stainless steels as received by the internal nitriding model, which is analogous to the internal oxidation model. it is demonstrated that the method predicts the correct temperature dependence of the nitrogen diffusion coefficient contrary to the internal nitriding model. The calculated sputtering rate is in good agreement with that estimated in the frame of Thornton's ion plating model. (C) 1998 Elsevier Science S.A.This work was performed at the Institute for Materials
Research, Limburg Universitaire Centrum, Belgium.
This text presents research results of the Belgium program on Interuniversity attraction poles initiated by the
Belgian State Prime Minister's Office (Brussels), Science
Policy Programming. One of the authors (V. I.D.) wishes
to acknowledge Limburg Universitaire Centrum for
financial support and hospitalit
Different tribological behavior of MoS2 coatings under fretting and pin-on-disk conditions
No full textThe performance of tribological coatings is often evaluated by fretting or pin-on-disk measurements. However, only a few papers dealt with the comparison of the two methods on the same coating. In this paper, a comparison of the tribological behavior of sputtered MoS2 coatings in fretting and pin-on-disk tests under different conditions is studied. The relationship between the mechanical properties of the coatings and their wear performance in both type of sliding tests is discussed. MoS2 coatings were deposited by magnetron sputtering from a MoS2 target. The coating thickness and adhesion were evaluated by respectively the ball crater and scratch test. The hardness as well as the toughness were obtained by a Vickers microhardness test. After the tribological tests the surface morphology of the wear scar in the coating was observed by scanning electron microscope. Also transfer films on the counterbody were investigated. It appears that the fretting and pin-on-disk tests can give considerably different friction and wear results. Coatings that show excellent performance in fretting tests have shown a low endurance in pin-on-disk tests. Sliding speed appears to be a crucial factor. Also the material of the counterbody, steel or corundum, influences the results in both tests in a different way. The different behavior of a coating in both tests is related to the toughness of the coating and to the way that the debris is involved in the friction and wear mechanisms. (C) 2002 Elsevier Science B.V. All rights reserved
Photocurrent and optical absorption spectroscopic study of n-type phosphorus-doped CVD diamond
No full textA low-temperature spectroscopic study of epitaxial phosphorus-doped n-type CVD diamond films deposited on a type-Ia diamond crystal, was been carried out using the constant photocurrent method (CPM). Two new defect levels in the gap of CVD diamond were detected. A numerical fitting of the optical cross-section data positions the first level, here denoted X-P1, at an optical excitation energy of 0.55 eV. The second level, denoted X-P2, is positioned at about 0.8 eV. The 0.55 eV energy obtained from the fitting procedure is in good agreement with Hall measurements of the activation energy of the carrier concentration for low P-doped samples. SIMS measurement shows a concentration of about 1 part per million (ppm) of phosphorus in the film. (C) 1999 Elsevier Science S.A, All rights reserved
Study by means of photothermal deflection methods of the opto-electronic properties of CVD diamon in relation to the defect population
No full textThe main objective of this thesis was to investigate if Photothermal Deflection Spectroscopy (PDS) could be applied to study the defects present in undoped and doped polycrystalline CVD diamond films. Up till now, PDS was only used for the characterisation of semiconductors such as a-Si and a-Ge. Photothermal Deflection Spectroscopy: PDS is a very sensitive characterisation technique which allows to determine the defectinduced optical absorption coefficient α of semiconducting films. We have adapted the PDS set-up in such a way that it meets the specific requirements of polycrystalline CVD diamond films and moreover, we studied the validity of the PDS theory for diamond. This resulted in the construction of two different PDS configurations: the transverse and the collinear set-up. (i) Transverse PDS was used for the first time as a gap state spectroscopic tool to study the optical transitions due to the presence of defects in the bandgap of diamond. The spectral dependence of the optical absorption coefficient α in the energy range of 0.5 to 5.4 eV can be studied. (ii) Collinear PDS was used to map the optical absorption (in our case at the CO2 laser wavelength of 10.6 µm, with a spatial resolution of about 100 µm) in high quality CVD diamond windows. In general, it is not straightforward to get absolute optical absorption values out of PDS measurements in arbitrary units. (i) We compared different scaling procedures for transverse PDS measurements to calculate the absolute optical absorption coefficient. - low quality CVD diamond films: Ssat-scaling procedure (transverse PDS + saturation value). - intermediate to high quality CVD diamond films: T-scaling procedure (transverse PDS + transmission measurements) (ii) In the case of collinear PDS, absorption values of high quality diamond films were calibrated by means of laser calorimetry on a reference sample. (Our collinear arrangement is not suitable to measure absorption in low quality diamond films.) In particular, the influence of light scattering in diamond films on transverse PDS measurements has been studied thoroughly. In the low absorption range (αd < 1), the effect of scattering and light trapping results in an artificially increased effective optical thickness. This enhancement is spectral independent and thus, the shape of the spectrum is not distorted. Actually, it comes down to an enhancement of the sensitivity of PDS. Since we measure PDS spectra in arbitrary units this influence is not relevant. In contrast with the transmission measurements, the PDS measurements are not hindered by scattering losses. Because specular transmission measurements suffer much more from scattering than integrated sphere transmission measurements, the latter are used to scale the PDS measurements...
Bipolar pulsed sputtering of MoSx coatings: plasma diagnostics, micro-structural and tribological study
No full textMoSx coatings were deposited by magnetron sputtering of an MoS2 target in an argon atmosphere with different process parameters. Their composition, surface morphology and structure were determined, and the friction and wear behaviour of these coatings were evaluated under fretting tests in air of< 10% and 50% or even 90% RH. The results obtained in this thesis indicate that the properties of sputtered MoSx films are influenced in a complex manner by the main process parameters. To establish a deep understanding between these parameters, the micro-structural properties and the tribological properties of the MoSx films, the energy distribution of neutral and ionised particles impinging on the growing film was studied by means of energy resolved mass spectrometry. T he results can be summarised as follows: MoSx coatings can be prepared either with the basal (002) planes oriented parallel to the substrate or with random or preferential edge orientation. Films with basal plane orientation are only obtained when they are deposited by bipolar pulsed sputtering at 0.4 Pa argon pressure and with a target current of 0.6 A. These films have a low sulphur to molybdenum ratio, contain approximately 4 At% Ar and exhibit a dense and featureless morphology. Using BPDC sputtering at high argon pressures or different target currents or using UPDC or DC sputtering results in films with a preferential edge or random orientation. Generally, these films have a higher sulphur to molybdenum ratio, a lower argon content and show a porous, worm-like morphology. ... (Excerpt from the conclusions
Bipolar pulsed sputtering of MoSx coatings: plasma diagnostics, micro-structural and tribological study
No full textMoSx coatings were deposited by magnetron sputtering of an MoS2 target in an argon atmosphere with different process parameters. Their composition, surface morphology and structure were determined, and the friction and wear behaviour of these coatings were evaluated under fretting tests in air of< 10% and 50% or even 90% RH. The results obtained in this thesis indicate that the properties of sputtered MoSx films are influenced in a complex manner by the main process parameters. To establish a deep understanding between these parameters, the micro-structural properties and the tribological properties of the MoSx films, the energy distribution of neutral and ionised particles impinging on the growing film was studied by means of energy resolved mass spectrometry. T he results can be summarised as follows: MoSx coatings can be prepared either with the basal (002) planes oriented parallel to the substrate or with random or preferential edge orientation. Films with basal plane orientation are only obtained when they are deposited by bipolar pulsed sputtering at 0.4 Pa argon pressure and with a target current of 0.6 A. These films have a low sulphur to molybdenum ratio, contain approximately 4 At% Ar and exhibit a dense and featureless morphology. Using BPDC sputtering at high argon pressures or different target currents or using UPDC or DC sputtering results in films with a preferential edge or random orientation. Generally, these films have a higher sulphur to molybdenum ratio, a lower argon content and show a porous, worm-like morphology. ... (Excerpt from the conclusions
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