Prague, Czech Republic
Prague, Czech Republic

Time filter

Source Type

Kadlec S.,HVM Plasma | Capek J.,University of West Bohemia
Journal of Applied Physics | Year: 2017

A tendency to disappearing hysteresis in reactive High Power Impulse Magnetron Sputtering (HiPIMS) has been reported previously without full physical explanation. An analytical model of reactive pulsed sputtering including HiPIMS is presented. The model combines a Berg-type model of reactive sputtering with the global HiPIMS model of Christie-Vlček. Both time and area averaging is used to describe the macroscopic steady state, especially the reactive gas balance in the reactor. The most important effect in the presented model is covering of reacted parts of target by the returning ionized metal, effectively lowering the target coverage by reaction product at a given partial pressure. The return probability of ionized sputtered metal has been selected as a parameter to quantify the degree of HiPIMS effects. The model explains the reasons for reduced hysteresis in HiPIMS. The critical pumping speed was up to a factor of 7 lower in reactive HiPIMS compared to the mid-frequency magnetron sputtering. The model predicts reduced hysteresis in HiPIMS due to less negative slope of metal flux to substrates and of reactive gas sorption as functions of reactive gas partial pressure. Higher deposition rate of reactive HiPIMS compared to standard reactive sputtering is predicted for some parameter combinations. Comparison of the model with experiment exhibits good qualitative and quantitative agreement for three material combinations, namely, Ti-O2, Al-O2, and Ti-N2 © 2017 Author(s).

Capek J.,University of West Bohemia | Kadlec S.,HVM Plasma
Journal of Applied Physics | Year: 2017

Titanium and aluminum targets have been reactively sputtered in Ar +O2 or Ar +N2 gas mixtures in order to systematically investigate the effect of reduced hysteresis in reactive high power impulse magnetron sputtering (HiPIMS) as compared to other sputtering techniques utilizing low discharge target power density (e.g., direct current or pulsed direct current mid-frequency magnetron sputtering) operated at the same average discharge power. We found that the negative slope of the flow rate of the reactive gas gettered by the sputtered target material as a function of the reactive gas partial pressure is clearly lower in the case of HiPIMS. This results in a lower critical pumping speed, which implies a reduced hysteresis. We argue that the most important effect explaining the observed behavior is covering of the reacted areas of the target by the returning ionized metal, effectively lowering the target coverage at a given partial pressure. This explanation is supported by a calculation using an analytical model of reactive HiPIMS with time and space averaging (developed by us). © 2017 Author(s).

Joska L.,Institute of Chemical Technology Prague | Fojt J.,Institute of Chemical Technology Prague | Mestek O.,Institute of Chemical Technology Prague | Cvrcek L.,HVM Plasma | Brezina V.,Masaryk University
Surface and Coatings Technology | Year: 2012

The properties of DLC layers provide for their broad use in medical applications. Their tribological properties are frequently utilized in big joint implants, and their barrier effect offers another benefit. The present work studied corrosion behavior of DLC coatings formed on titanium and Ti6Al4V alloy with a titanium or chromium inter-layer, in environments to which dental implants may be exposed. Electrochemical impedance spectroscopy, XPS surface analysis, ICP/MS chemical analysis method and a set of standard biological tests were employed in the study.The behavior of both coated systems, regardless of the basic material, was comparable in an environment that did not contain fluoride ions. An addition of fluorides revealed the occurrence of pores as deep as the DLC layer even in specimens with a surface polished prior to coating. Porosity of layers was clearly evident on jet-blasted specimens. The best corrosion behavior was recorded in specimens with a chromium inter-layer on both types of the basic material. With the titanium inter-layer applied, coatings on TiAlV exhibited higher corrosion resistance than those on commercial-pure titanium. The conducted biological tests indicated applicability of a chromium inter-layer on DLC coated implants. © 2012 Elsevier B.V.

Joska L.,ICT in Prague | Fojt J.,ICT in Prague | Cvrcek L.,HVM Plasma | Brezina V.,Masaryk University | Malek J.,UJP Prague
METAL 2012 - Conference Proceedings, 21st International Conference on Metallurgy and Materials | Year: 2012

Properties of DLC (diamond-like carbon) layers provide for their broad use in medical applications. Their tribological properties are frequently utilized in big joint implants. Another benefit is offered by their barrier effect. In the frame of presented work the corrosion behavior of DLC-Ti alloyed coatings formed on TiNbTa alloy in environments to which dental implants may be exposed was studied. Electrochemical impedance spectroscopy, XPS and a cell colonization test were employed in the study. Influence of DLC alloying by titanium was tested on samples with 3 levels of titanium amount. According to results of XPS analysis, surface concentration of titanium was 3.4, 10.2 and 23.6 at.%. Unambiguous and marked peak of titanium carbide was detected only in the case of highest concentration of titanium. Corrosion resistance of TiNbTa/Ti/DLC and TiNbTa/Ti/DLC-Ti was in low-aggressive physiological solution slightly different nevertheless very high in both cases. Electrochemical behaviour of carbon was significantly suppressed by titanium; character of EIS spectra was more capacitive than in the case of pure DLC. Decrease of pH did not influence the level of charge transfer resistance (polarization resistance). The main disadvantage of titanium - sensitivity to fluorides - was emphasized by alloying. Colonization by cells was slightly increased on alloyed samples in comparison with unalloyed DLC.

Joska L.,Institute of Chemical Technology Prague | Fojt J.,Institute of Chemical Technology Prague | Hradilova M.,Institute of Chemical Technology Prague | Hnilica F.,UJP | Cvrcek L.,HVM Plasma
Biomedical Materials | Year: 2010

Nowadays, a wide range of materials for human implants is used. To reach the required properties of implants, coatings are applied in some cases. This contribution is focused on the corrosion properties of TiN and ZrN layers on cp-titanium (commercially pure titanium) under environment modelling conditions in an oral cavity. Measurements were done in artificial saliva and a physiological solution unbuffered and buffered to a pH value of 4.2 with the addition of fluoride ions up to 4000 ppm. Standard corrosion electrochemical techniques were applied. Both types of layers were stable in both model saliva and physiological solution with non-adjusted pH. The decrease in pH to 4.2 resulted in a minor decrease of corrosion resistance in all cases, but polarization resistance was still in the order of 105 Ω cm 2. An important change in a specimens' behaviour was noticed in the presence of fluoride ions. TiN was stable in the highest concentration of fluorides used. The ZrN layers were destabilized in an environment containing a few hundred ppm of fluoride ions. As for TiN, the decisive factor is the influence of porosity; the corrosion resistance of ZrN is limited. From the corrosion point of view, the application of the TiN-based barrier layers in dental implantology is more advisable than the use of ZrN, provided that the application of a barrier is inevitable. © 2010 IOP Publishing Ltd.

Loading HVM Plasma collaborators
Loading HVM Plasma collaborators