Papers by Keyword: Ceramic Coating

Abstract: Micro-arc oxidation coating on ZAlSi12Cu2Mg1 alloy were prepared in Na2SiO3 electrolyte, effects of C6H8O7 and C3H8O3 as additive on resistances of micro-arc oxidation coatings were investigated. Results show that coatings containing completest ceramic particles were obtained on alloys surface processed in electrolyte solution including 2.0 g/L C6H8O7 additive, the size of micro-arc wholes becomes larger with more C6H8O7, and it has improved with 1ml/L C3H8O3 in the solution. The results of XRD analysis indicates that the coatings are mainly composed of alumina and mullite. EDS analysis showed the element contains sodium, oxygen, silicon and aluminum. Wear resistance of coating were increased by adding C3H8O3.

Abstract: aluminum nitride ceramic coating were obtained on LY12 aluminum alloy by plasma electrolytic oxidation in CO(NH₂)₂ electrolyte. The microstructure of the ceramic coating including phase and elements composition, surface and cross section morphology were investigated. The properties of the ceramic coatings such as surface roughness, thickness and bonding strength were primarily studied. The results show that the ceramic coating on LY12 aluminum alloy surface was AlN coating with the thickness of 12 um. The AlN ceramic coating showed rough and porous. The average diameter of the pores was 6 um and the surface roughness was 1.5 um. The bonding strength of the coating was 18 ± 2 MPa.

Abstract: Self-lubricative ceramic coatings were prepared on Q235 carbon steel by plasma electrolytic oxidation (PEO) in aluminate electrolyte containing graphite. The microstructure of the PEO coatings were examined. Influence of graphite in electrolyte on the coating growth properties was analyzed according to the voltage vs. time plots. Effect of graphite concentration on the properties of the coatings such as bonding strength, surface roughness and thickness were studied. The tribological behavior of the coating was primarily evaluated.The results showed that the self-lubricative coatings consisted of FeAl₂O₄, Fe₃O₄ and a certain amount of graphite. With increasing the concentration of graphite in the electrolyte, the coating growth gradually became stable with lower breakdown voltage and end voltage. The bonding strength and the thickness of the coating were not strongly affected by the graphite concentration whose value remained approximately 19Mpa and 110μm, respectively. With increasing the graphite concentration, the surface roughness first decreased and then increased a little. The friction coefficient of the coatings also varied with the concentration of graphite. When the concentration of graphite was 8 g/l, the tribological property of the coatings was the most excellent with the friction coefficient bellow 0.1.

Abstract: The ceramic coatings, on the substrate of LY12 Al alloy, were prepared by micro-arc oxidation (MAO) technique with different electrical source parameters. The microstructure and tribological properties of the resulting micro-arc oxidation ceramic coatings(MAOC) were tested and analyzed by Nano-scratch tester, Micro-hardness tester and ball-on-disk friction tester etc. The results indicate that the thickness, roughness, micropore sizes and wear-resistance of MAOC increase with impulse frequency decreasing, however, the porosity is correspondingly reduced.

Abstract: Al₂O₃ and Al₂O₃-40wt.%TiO₂ ceramic coatings on H13 hot-worked die steel have been prepared by plasma spraying, and then the microstructure, micro-hardness as well as wear resistance of the prepared coatings have been investigated by means of x-ray diffraction (XRD), scanning electron microscope (SEM), Vickers hardness tester and ball-on-disk high temperature tribometer. The results showed that the plasma sprayed ceramic coatings are of higher hardness and wear resistance than H13 hot-worked die steel.

Abstract: Ceramic coatings were fabricated by plasma arc oxidation on Ti₆Al₄V alloy in phosphate –containing solution. The growth rate, microstructure and phase composition of ceramic coatings were investigated using coating thickness gauge, scanning electron microscope (SEM) and X-Ray diffraction (XRD). After plasma arc oxidation treatment, the microstructure of the remained Ti₆Al₄V alloy substrate remains unchanged and no hardening zone in the substrate is found. Ceramic coating formed on Ti₆Al₄V alloy surface by alternating-current plasma arc oxidation contains two layers: an outer layer and an inner layer. The outer layer coating consists of a large amount of rutile and a little anatase. But in the inner layer, anatase becomes a main phase while the rutile fraction obviously decreases, which indicates that phase transformation of anatase into rutile occurs in the duration of oxidizing process. In the mean time, with increasing treatment duration, coating growth varies from rapidness to tardiness accompanied by gradually roughening in appearance.

Abstract: Adhesion is one of the most important mechanical properties of ceramic coatings. Scratch testing is considered as a simple and effective method to evaluate adhesion of ceramic coatings. In this paper, the critical normal forces and scratch morphologies for different coating-substrate systems were studied by scratch testing. It is shown that the critical normal force obtained by acoustic emission (AE) signals decreases from 12 N to 7 N when the applied normal force rate increases from 20 N/min to 100 N/min for CVD SiC on C, and the failure area of this scratched sample increases with increasing maximum normal force; Based on scratch morphologies, spallation or delamination can be observed for hard-brittle coatings on glass or metal, while discontinuous or continuous ductile perforation can be observed for ductile coatings on metal; The critical normal force for hard-brittle coatings can be effectively obtained by AE signals.

Abstract: Ceramic oxide coatings were produced on pure titanium by plasma electrolytic oxidation in different electrolytes. The variation of coating thickness with applied voltages revealed coating almost kept a steady-state growth rate in electrolyte A and B, but not for electrolyte C. Numerous nodules occurred on the surface of the coatings at 200V in electrolyte A and B, and then nodules disappeared with the applied voltage increasing to 300V. There was no nodules occurred, and pore size was evidently different in electrolyte C. When the applied voltage was 300V, the coating formed in electrolyte C exhibited the highest corrosion potential and lowest corrosion current density in 3.5% NaCl aqueous solution.

Abstract: Plasma Electrolytic Oxidation (PEO) is a powerful technique allowing hardening and corrosion protection of valve metals due to formation of an oxide layer on the metal surface. The addition of fluoride ions to the alkaline electrolyte for the PEO processing of aluminum and magnesium alloys produces significant changes in the structure and properties of the coating [1-, however the mechanism of these changes is not clear. A study of the influence of the fluoride concentration on the composition, structure and morphology of thin (to 20 µm) PEO layers was performed. The oxide layer thickness on aluminum is significantly smaller than that on magnesium. Fluorine is detected as an amorphous phase in the vicinity of the base metal.

Abstract: LY12 aluminum alloy samples were treated by microarc oxidation in sodium metasilicate electrolytes. The effects of treatment time on cell violate and ceramic coating thickness were investigated. The results indicate that the micro-arc oxidization process was divided into two stages, at the first stage, the cell voltage increased linearly at a very high rate of 70 V/min, at the second stage, in the range of 430-470 V, the cell voltage reached a relative stable value. The thickness of the coating increased linearly at the whole stage with increasing treating time. XRD analyses indicate that the ceramic coatings fabricated on the surface of aluminum alloys by micro-arc oxidization are composed of Al phase Al2O3 phase. SEM show that the maximum porosity of the ceramic coatings with distributing uniformly pore diameter are decreased with the increasing treatment time.