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Combined coatings against mechanical wear and corrosion low carbon steel
Brožek, Vlastimil ; Pokorný, P. ; Kolísko, J. ; Vokáč, M. ; Mastný, L. ; Stoulil, J.
In this study, special ceramic coatings were prepared on low carbon steel (1.0060 - EN 10027-2) via the plasma spraying technique using a WSP®-H plasma generator with output of up to 40 kg/h of aluminum oxide. Corundum coatings were deposited directly on the surface of steel plungers equipped with an anti-corrosion interlayer of zinc phosphate. Coating adhesion properties were tested using pin-off tests (modified ISO 4624) and reached a maximum value of 26 MPa. Corrosion resistance was evaluated by measurements of impedance spectra in the 100 kHz - 10 mHz range in a water solution of sodium sulfate. The capacity of electric double-layer varied depending on the porosity and thickness of the coating. Low-porosity coatings of >1.5 mm thickness had RCT 1.29·105 Ω·m2. The abrasive resistance of coatings was measured by rotary/machining test with SiC cutting knives, using a downforce of 50 kg·cm-2. Abrasion losses decreased with the quality of finish - starting at 0.00266 g cm-2 min-1 down to virtually zero losses after polishing the surface below Ra = 0.55 micro m.
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Black Chromia Plating for the Solar Radiation Absorbers
Brožek, Vlastimil ; Březina, Václav ; Brom, Petr ; Kubatík, Tomáš František ; Vilémová, Monika ; Mastný, L. ; Novák, M.
Black chromia layers were produced on copper, zirconium and aluminium substrates. These layers are aimed to serve as solar collectors. Efficiency of the layers during UV-VIS, UV radiation and WSP® plasma torch radiation is described. The chromia layers were prepared by a new procedure, i.e. deposition of ammonium dichromate solution using plasma torch or so called Liquid Precursor Plasma Spraying (LPPS). Solution of ammonium dichromate is fed into plasma stream, where dissociation takes place under temperatures of 4000 K – 25000 K. Up to nanometric oxide particles can be produced; the resulting size is dependent on solution concentration and feeding nozzle diameter. The particles impact on substrate and form coating. Using 2 wt.% to 5 wt.% solution of ammonium dichromate and feeding nozzle of 0.2 mm in diameter is the size of produced chromia particles about 6 µm which results in formation of 2 µm to 3 µm thick coating, i.e. according to the theory an optimal thickness 2.5 um for absorption layers, necessary condition for formation energy traps for IR radiation emitters up to 100°C. Moreover, black chromia coating is a suitable corrosion barrier of metallic substrates. \n\n
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Boronized stainless steel with zirconia coatings
Brožek, Vlastimil ; Kolísko, J. ; Kubatík, Tomáš František ; Mastný, L. ; Pokorný, P. ; Tej, P.
Conditions of boronizing are described using a reactive diffusion method of boron from boron carbide and lanthanum hexaboride so that the formation of Fe2B is preferred to FeB which is more brittle and whose structure does not satisfy the conditions for perfect adhesion of modified zirconia ceramics. Perfectly rigid adhesive connection of needle-like embedded interlayers Fe2B in steel AISI 303 prepared by reactive diffusion of a boronizing medium without activators at 1000 ° C and exposure of 2-4 hours has the value of 20 - 24 MPa at the Pinn-off test.Ceramic coatings from Al2O3-ZrO2 ceramics formed on those interlayers have the value of bond strength up to 14 - 20 MPa.Thermal cycling between 100°C - 600 °C confirmed good adhesion of coatings with the underlying steel.During thermal cycling at elevated temperatures (600-1000 °C) there occurs a statistically significant number of faults in cohesion and mechanical destruction of the coatings. One of the reasons are secondary changes
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Plasma coatings of phosphated steels II
Pokorný, P. ; Mastný, L. ; Brožek, Vlastimil
This article follows the introductory part, presented at the conference APROCHEM 2012 and evaluates the possibility of using different kind of phosphate coatings for the pretreatment of mild steel intended for plasma sprayed ceramic coatings. The phosphate conversion coating has to improve the corrosion resistance of coated steel and also to improve and extend the adhesion of ceramic coating to mild steel surface. Selection the most appropriate phosphate coating (zinc, zinc-calcium, manganese and „three-cations“ phosphate) was established to study the dehydration curves by means of DTA and TGA analysis with subsequent analysis of morphology, integrity and composition of the coating after each dehydration section.Samples were exposed at 200 °C for 10 hours.The measurement results showed that the most stable is manganese phosphate. Plasma deposition of corundum was carried out low-temperature plasma generator WSP ®. The corrosion resistance of coated samples with different phosphate
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Improving Bond Strenght between Carbon Steel and Plasma Sprayed Ceramics by Phosphating Process
Pokorný, P. ; Brožek, Vlastimil ; Mastný, L.
Phosphating is currently the highest standard of surface treatment before painting in the vehicle industry. Excluded phosphate crystal layer is due to its high porosity absorbing not only paints but also oil and lubricants that can reliably maintain the surface. Improved bond strenght in the case of coatings exposed in the humid atmospheres in comparison with multiple non-coated surface. Focus of this work is an effort to improve the bond strenght between the diferent plasma-sprayed coatings materials and carbon steel using different phosphate coatings. Because most of the eliminated phosphate crystallizes with four crystal waters the samples was covered by zinc-calcium phosphate, which crystallizes with only two waters [scholzite: Zn2Ca(PO4)2 . 2H2O] and coated from bath of „three-cationts“ phosphate due to the large thickness of the coating and compaction [fosfofylit: Zn2Fe(PO4)2 . 4 H2O]. They decided test for measuring the quality of bond strebght between coating and steel
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Ceramic coatings prepared by liquid precursor plasma spraying
Brožek, Vlastimil ; Kutílek, Zdeněk ; Bertolissi, Gabriele ; Mastný, L.
LPPS method (Liquid precursor plasma spraying) was performed using aqueous solutions of ammonium vanadate and chromate in order to přepade nano-crystalline ceramic coatings on steel and ceramic substrates. Their structure was studied and verified by injecting at different conditions the liquid precursors into the stream of water stabilized plasma. The surface coverage of nano-coatings is inversely proportional to the concentration of precursor and largely depends on the geometric arrangement of the depositing device in which there is a complex process multistage precursor processing within milliseconds.
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Interakce trhliny a kovového substrátu v plasmových keramických nástřicích
Náhlík, Luboš ; Knésl, Zdeněk ; Kroupa, František
Plasma-sprayed ceramic coatings contain a high density of intrasplat microcracks which are responsible for small YoungŽs moduli and low fracture toughness. The extension of an initial surface crack in the direction to the interface, where the crack is repelled by the metal substrate with higher YoungŽs modulus, is studied using the methods of fracture mechanics. It is shown that high tensile stresses induced by the crack in the interface can lead to a local decohesion along the interface so that the crack can deviate into the interface
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