Papers by Keyword: Plasma Electrolytic Oxidation (PEO)

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Authors: Hai He Luo, Qi Zhou Cai
Abstract: A ZrO2-Y2O3-containing composite ceramic coating was firstly in situ prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline silicate-containing electrolyte. The morphology, chemical composition and corrosion resistance of the PEO coating were investigated by environmental scanning electron microscopy (ESEM), X-ray diffractometer (XRD), energy dispersive X-ray (EDX) spectrometer, dropping corrosion and electrochemical corrosion test. The results showed that the ceramic coating consisted of two distinct structural layers: an outer loose layer and an inner dense layer; it was composed of t-ZrO2, Y2O3, SiO2 and some magnesium compounds, such as MgO, MgF2 and Mg2SiO4. In addition, the ceramic coating also showed excellent dropping and electrochemical corrosion resistance, which was mainly attributed to its special phase composition and microstructure.
Authors: Myoung Ryul Ok, Eun Young Kang, Ji Hye Kim, Young Su Ji, Chang Woo Lee, Young Joo Oh, Kyung Tae Hong
Abstract: Plasma electrolytic oxidation (PEO) has drawn attention and been studied intensively all through the world. The thick ceramic coatings fabricated by the technique exhibit excellent properties, including hardness and wear resistance, thermal and electrical insulation, and corrosion resistance, due to the characteristic phase composition and microstructure of the coating layers. However, most of the studies have dealt with manufacturing process itself and the apparent properties of coating layers and researches on the microstructural basis including transmission electron microscopy analysis are limited so far. In this investigation, a basic approach to PEO process was tried, adapting time-potential behavior analysis under constant current mode (galvanostatic) oxidation, and microstructural analysis on the coating structure, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The time-potential behavior analysis under constant current DC was carried out, and the resultant evolution of the microstructure was characterized..
Authors: Li Shi Wang, Chun Xu Pan, Qi Zhou Cai, Bo Kang Wei
Abstract: This paper reports the heat-resistance of plasma electrolytic oxidation (PEO) coatings formed on AZ91D alloy in phosphate electrolytes (P-film) and silicate electrolytes (Si-film). The results showed that the P-film was mainly composed of MgAl2O4, MgO and the Si-film was composed of Mg2SiO4, MgO. Thermoanalysis results verified that all these phases contained in the two type coatings had excellent thermal stability below 800oC. Meanwhile, the total area of heat erosion formed on the surface of samples tended to be increased with the exposure time prolonged in high temperature (410 oC and air atmosphere).
Authors: Yong Feng Jiang, Hua Shan Yang, Ye Feng Bao, Ying Yue Zhang
Abstract: The composite coatings were prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) plus cathodic electrophoretic deposition (E-coat) to improve corrosion protection. SEM observation revealed that the organic layer was integrated with PEO film by physically interlocking; Potentiodynamic polarization(E-i) measurements in 3.5% NaCl solution, copper accelerated acetate salt spray(CASS) test and immersion test were employed to evaluate corrosion principle and corrosion rate of composite coatings. It is indicated that the corrosion resistance of composite coatings was improved obviously compared to the PEO film. There is no noticeable pitting corrosion on the composite coatings after 320h CASS test. The adhesion of composite coatings was evaluated by cross-cut and pull-off test. The results show that adhesion of composite coatings can reach to level 0 and 11.3 N/mm2 as a result of the blocking effect between organic layer and PEO film.
Authors: In Jun Hwang, Kang Min Lee, Bong Young Yoo, Dong Hyuk Shin
Abstract: Characterization of nickel oxide layers on the AZ91 Mg alloys by plasma electrolytic oxidation (PEO) was investigated. For this purpose, PEO coating was carried out on the present sample in the alkaline electrolyte with nickel ion at three different voltage responses, i.e., 150, 250, 350 V. The amount of nickel oxide increased by increasing process time, and changed the color of sample from light grey to moderate olive brown. It was observed from potentio-dynamic polarization analysis that polarization resistance of oxide layer was increased with increasing nickel ions. Also microhardness of the sample processed at 350 V was higher than those of the samples.
Authors: Li Wang, Li Chen, Wen Fu
Abstract: Plasma electrolyte oxidation films (PEO) on AZ31 magnesium alloy were prepared in alkaline silicate solutions with two kinds of voltage waveforms (constant voltage waveform and escalating voltage waveform). Discharge characteristics and the dielectric barrier layer formation of the films formed under two voltage waveforms were investigated. Structure, composition, morphology and corrosion resistance characteristics of the films were studied with scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and potentiodynamic corrosion testing. The porosity of the films was calculated with Mat lab software. Structure, composition and porosity of the films are correlated with changes in behaviors of spark discharges on the surface in oxidation process. The escalating voltage waveform strongly affects the transformation of Mg2+ from the substrate but not the SiO32- ions in the electrolyte and the compactness of dielectric barrier layer. The films formed under escalation voltage waveform exhibited lower porosity and higher corrosion resistance than the films formed under constant voltage waveform because of less defects on the surface of the films. The voltage waveform change has little influence on the thickness of the films.
Authors: Krzysztof Rokosz, Tadeusz Hryniewicz, Winfried Malorny
Abstract: The main goal of present paper is to obtain porous coatings enriched in copper by Plasma Electrolytic Oxidation on titanium and niobium as well as on NiTi and Ti6Al4V alloys. Performed SEM and EDS studies confirmed the hypothesis that it is possible to create the porous surfaces with pores, which shapes and size are different. In order to show the copper enrichment inside the surface layers, the copper-to-phosphorus ratios were used. Based on these ratios it may be concluded that average value of Cu/P is maximal for NiTi alloy after oxidation in electrolyte containing 300 g of copper nitrate in 1 liter of phosphoric acid and equals 0.26. The minimum of Cu/P ratio equaling to 0.12 was recorded for pure titanium and pure niobium treated in electrolyte containing 300 g of Cu (NO3)2 in 1 L H3PO4.
Authors: A. Venugopal, J. Srinath, P. Ramesh Narayanan, S.C. Sharma, Koshy M. George
Abstract: The electrochemical corrosion and mechanical properties of ceramic coatings fabricated by plasma electrolytic coating (PEO) and hard anodizing (HA) methods comparatively examined for AA2219. Potentiodynamic polarization results revealed that the corrosion resistance of both coatings are comparable to each other. However, the indentation and scratch testing indicated that the hardness and modulus of the PEO coating was significantly higher when compared to HA coating. The critical load (Lc2) causing adhesive failure of the PEO coating was much high (19N) when compared to HA coating (10N) showing better adhesive strength of the PEO coating.Key words: Plasma electrolytic oxidation (PEO), potentiodynamic polarization, nanoindentation, hard anodizing
Authors: Li Wang, Li Chen, Wen Fu
Abstract: The aim of this work is to discuss the corrosion characteristics of plasma electrolytic oxidation (PEO) films formed on AZ31 magnesium alloys in alkaline silicate solution. The uniform and pitting corrosion resistance of the PEO films was investigated by potentiodynamic polarization tests and potentiodynamic scanning curve tests. The composition, the structure and the element contents of the films after immersed in 3.5 wt.% NaCl solution for different time were investigated by XRD、SEM and EDS. The results indicated that the corrosion occurred on AZ31 magnesium alloy and treated PEO samples during five days immersion, but the corrosion tendency of the PEO treated samples is smaller than that of AZ31 magnesium alloy.
Authors: Li Wang, Wen Fu, Li Chen
Abstract: The corrosion mechanisms of plasma electrolytic oxidation (PEO) films formed on AZ31 magnesium alloys were discussed in alkaline silicate solution. The structure and element contents of the films after immersed in 3.5 wt.% NaCl solution were investigated by SEM and EDS. The results indicated that the corrosion occurred on AZ31 magnesium alloy and the treated PEO samples during five days immersion. The corrosion procedure of the samples was depicted.
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