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Ceramo-metallic materials of the Ti-B-C and Ti-B-N systems
Brožek, V. ; Doležal, J. ; Novák, M. ; Ctibor, Pavel ; Kolman, Blahoslav Jan
Products prepared by the sintering of titanium and boron carbide powder and by the sintering of titanium and boron nitride powder were studied. The sintering was performed at 2,000 °C under the pressure of 6 GPa in a high-pressure apparatus of BELT-type with sufficient holding time to reach thermodynamic equilibrium. The results of chemical and phase composition analyses were compared with thermodynamic prediction of possible reactions in the system. We proved the preferential formation of borides TiB and TiB2 prior to the carbides or nitrides formation. The products, which may be considered Ti-(TiB,TiB2)-TiN or Ti-(TiB,TiB2)-TiC cermets, were analysed in order to determine their microstructure, phase and chemical composition and their influence on mechanical properties such as hardness or elastic modulus. This work precedes similar study which will be performed using the same powders processed by plasma spraying, which enables to stabilize high-temperature phases by rapid cooling.
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Microstructure and performance of titanium oxide coatings sprayed by oxygen-acetylene flame
Ctibor, Pavel ; Štengl, Václav ; Zahálka, F. ; Murafa, Nataliya
TiO2 nano-powders were agglomerated by a spray drying process for applying to thermal spraying. A conventional oxygen-acetylene flame torch was used to deposit porous partially nanostructured TiO2 coatings. Steel substrates were used as a support for tested samples. Scanning Electron Microscopy, X-ray microanalysis and X-ray diffraction were performed to study the morphology and the crystalline phases of the titania coatings. Optical bandgap and kinetics of the acetone decomposition was studied too. The best results were obtained for the powder which is available as a commercial spray feedstock. This powder seems to be most resistant against the reducing atmosphere in the jet of combustive gasses.
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Tungsten cermets with zirconium and hafnium carbides
Brožek, Vlastimil ; Ctibor, Pavel ; Matušek, M. ; Sedláček, J.
Cermets with tungsten matrix and functional components of ZrC and HfC with absolutely highest meeting points are materials with good properties at high temperature exposure. Tungsten based cermets with 10, 20 and 30 % of the functional component were prepared by two different procedures and their properties were compared. The first series of the samples was manufactured by powder metallurgy. A homogenized and preformed mixture of powders was sintered at 2000°C and pressure 6 GPa by hot-pressing technique in the apparatus of BELT-type. The second series was prepared by plasma spraying with water-stabilized plasma WSP® by two different procedures. In the first case the powders of W and ZrC (or W and HfC) were injected into the plasma jet by two separate feeders. The feeding distance 25 to 75 mm was affected by different kinetic parameters, different size distribution and density. The second case represents deposition of pre-spheroidized powder mixtures prepared by spray drying
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Plasmachemical synthesis of borides, carbides and nitrides of transition metals
Brožek, Vlastimil ; Ctibor, Pavel
For technical practice the most important are up to now borides of titanium and zirconium, carbides of boron, calcium, silicium, titanium, zirconium, hafnium, aluminum and chromium. Nitrides of boron, silicium and titanium. Besides of tungssten carbide, any of the mentioned compounds is proced presently in the Czech Republic, however the know-how and suitable conditions are existing. The contribution describes possibilities of the processing of the mentioned materials to functional layers or thin-walled shaped parts by plasmachemical methods.
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Cermety z karbidu hafnia
Brožek, Vlastimil ; Ctibor, Pavel ; Dong-Ik, Ch. ; Eun-Pyo, K.
Cermets of the HfC in W matrix were prepared firstly by hot pressing at the temperature 2000°C and pressure 5.5 GPa and secondly by plasma spraying using water stabilized plasma gun WSP. Microhardness, elastic modulus and thermal expansion coefficients were measured for 10 % HfC and compared with pure tungsten.
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Improvement of mechanical properties of the sintered ceramics by plasma remelting
Ctibor, Pavel
Ways how to improve mechanical properties on a surface of bulk ceramics are drawn. In the experiments the author reach surface treatment by plasma torch producing thermal plasma and usually utilized for plasma spraying. Commercial bulk ceramic materials produced via sintering or casting were tested. The materials were members of ternary systems magnesia - alumina - silica and zirconia - alumina - silica. Before and after thermal treatment the microstructure was studied and the microhardness was measured on materialographically polished cross sections using Vickers indentation (HV) in surfacial layers and also deep inside the bulk body. Slurry abrasion resistance (SAR) was determined according ASTM G 75 standard. Various degree of improvement of HV and SAR was detected on treated samples. The microstructural character of completely remolten surfacial layer, partly influenced intermediate layers and original bulk body is discusses in connection with evaluated mechanical tests.
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Elektrická rezistivita podstechiometrického TiO2 vyrobeného plazmovým nástřikem
Ctibor, Pavel ; Sedláček, J. ; Neufuss, Karel
The work is concentrated on electric resistivity of plasma sprayed titania TiO2. Synthetic conventional TiO2 powder and powder prepared by agglomeration of nanopowder particles were sprayed and measured. Spraying was carried out using the water-stabilized plasma system (WSP®) and resistivity measurement was applied on TiO2 layers detached from the substrate. Variations in basic spray conditions – spray distance, feedindg distance and substrate preheating temperature were commented from the point of view of their influence on electric resistivity.
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Kvantifikace struktury žárovových nástřiků s pomocí objemové rekonstrukce
Ctibor, Pavel ; Lechnerová, R. ; Hofmann, P.
The paper introduces a way to study structure of thermally sprayed coatings in detail. Two microstructures are compared, which originate from two different spraying techniques used for the same material. The material selected is stainless steel AISI 316L and the techniques are plasma spraying using water-stabilized plasma gun and wire arc spraying. A sophisticated analytical technique is applied which was developed for a 3D reconstruction of the architecture of thermally sprayed coatings, revealing their main characteristic structural features such as porosity and oxide phase. The technique is called 3D mapping and describes the shape of pores, their interactions, etc. It is based on optical microscopy and software treatment of microstructural images. Also it is possible to detect pores or the structural phases, provided that they can be separated by proper threshold. This method is here applied first time on wire arc sprayed coating and also on metallic coating containing oxides.
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Elektrická rezistivita podstechiometrického TiO2 vyrobeného plazmovým nástřikem
Ctibor, Pavel ; Sedláček, J. ; Neufuss, Karel
The work is concentrated on electric resistivity of plasma sprayed titania TiO2. Synthetic conventional TiO2 powder and powder prepared by agglomeration of nanopowder particles were sprayed and measured. Spraying was carried out using the water-stabilized plasma system (WSP®) and resistivity measurement was applied on TiO2 layers detached from the substrate. Variations in basic spray conditions – spray distance, feedindg distance and substrate preheating temperature were commented from the point of view of their influence on electric resistivity.
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