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6061 aluminium was treated by Plasma electrolytic oxidation (PEO) where a new experimental method was introduced: the applied voltage of the PEO process was quickly increased to 486 V by different ...

Various plasma electrolytic oxidation (PEO) ceramic coatings were fabricated on aluminum in the electrolytes with different concentrations of Na2SiO3·9H2O. The morphology of fractured cross-section and coating/substrate (C/S) interface, phase compositions, and corrosion behavior of these ceramic coatings were characterized employing field emission scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffractometer (XRD), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results showed that adding Na2SiO3·9H2O in the electrolyte could reduce the decrease amplitude of the voltage-time curve, and it can affect the types of the anodic film before the beginning of plasma discharges. A novel phenomenon was recorded as PEO treatment was carried out in the electrolyte with 1.85 g l−1 Na2SiO3·9H2O that the substrate was first covered by a barrier-type anodic film, and then a porous-type anodic film appeared after the barrier-type anodic film was broken down. The anodic film continued to grow for a long duration in the PEO process after being broken down. Characteristics of PEO ceramic coatings with a similar thickness acquired in various electrolytes were also evaluated. XRD results indicated that these ceramic coatings of similar thickness were mainly composed of α-Al2O3 and γ-Al2O3, and the α-Al2O3 proportion decreased with increasing Na2SiO3·9H2O concentration. The electrochemical data showed that the corrosion resistance of these PEO ceramic coatings of similar thickness decreased by adding Na2SiO3·9H2O in the electrolyte.

Plasma electrolytic oxidation (PEO) of Al was carried out in dilute alkaline sodium tripolyphosphate (Na5P3O10) electrolyte. Surface and cross-section morphologies, elemental and phase compositions were characterized by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometer (XRD). The results revealed that a severe thinning of the anodic film resulted in the voltage decrease at the initial stage of the PEO process. Porous-type anodic film with uniform pore diameter were fabricated at the initial stage of PEO process. Subsequently, detachments and cracks took place on the anodic films, and served as weak regions occurring dielectric breakdown preferentially due to the concentration of electric current at these sites. Two origins of PEO coatings, the transformation of anodic films and the normal generation of PEO coatings through the plasma discharges, were proposed. The results also indicated that P element mainly participated in the anodic oxidation and existed as amorphous phase in the inner side areas of anodic films except the barrier layer. Based on the analyses of the microstructure evolution and the chemical composition, a schematic of coating growth mechanism was proposed in the end.

In this work, a new type of Ti-Se conversion coating was formed on the surface of an aluminum alloy using titanium and selenide as the main salts. An examination of the surface morphology, composition and microstructure of the conversion coating was done using scanning electron microscopy, energy-dispersive spectrometry and x-ray photoelectron spectroscopy. The results showed that the surface of the conversion coating possessed a reticular structure with uniform cracks and a dense coating with a thickness of 0.4 μm. The elements in the conversion coating were C, O, Ti, Al and Se. The corrosion resistances of both the Ti-Se conversion coatings and the bare substrate were evaluated by an immersion test, polarization curves and electrochemical impedance spectroscopy. The results showed that the corrosion current of the conversion coating improved the corrosion resistance of the aluminum alloy and effectively protected the aluminum alloy in the immersion test. Furthermore, the corrosion current obtained from the polarization curves and electrochemical impedance spectroscopy decreased by one order of magnitude after the formation of the Ti-Se conversion coating, suggesting an improvement in polarization resistance.

A plasma electrolytic oxidation (PEO) coating was fabricated on AA1060 alloy in an alkaline sodium hexametaphosphate ((NaPO3)6) electrolyte. The growth characteristic of the PEO coating was investigated by means of a substrate-detachment technique, Scanning electron microscope (SEM) equipped with energy dispersive spectrometry (EDS), X-ray photoelectron spectrometer (XPS), X-ray diffractometer (XRD) and Mott-Schottky analysis. The results showed that an ordered and porous anodic aluminum oxide (AAO) film was formed at the anodic oxidation stage by the influence of (NaPO3)6 in the electrolyte, and the microstructure of the AAO film induced the plasma discharge events to initiate inside the AAO film. The Mott-Schottky analysis showed that the PEO coated samples were all represented n-type semiconducting behavior. The microstructures of detached coatings showed that the coating/substrate interfaces formed at the anodic oxidation stage and sparking stage consist of numerous hemispherical cap structures, but with different sizes. It was also revealed that the inward growth of the hemispherical cap structures is dependent on the diffusion of oxygen from the electrolyte or plasma gases to substrate, and P atoms mainly exist in the amorphous phase of the PEO coating.

Plasma electrolytic oxidation (PEO) coatings were prepared on AA1060 alloy substrate by a galvanostatic regime in an alkaline sodium hexametaphosphate ((NaPO3)6) electrolyte, and the influences of ...

Evolution of M23C6 carbide during isothermal aging of the 10% Cr martensite ferritic steel at 650 °C has been investigated by mainly using SEM-BSE and TEM-EELS. It was found that the M23(C,N)6 carbonitride formed after aging for 27,000 h since nitrogen atoms replacing part of carbon atoms dissolved into the M23C6 carbide. Such M23(C,N)6 carbonitride exhibited high stability as compared with previous M23C6 carbide. The size of M23(C,N)6 hardly changed even if the duration of aging exceeded 36,700 h, keeping at the level of ~200 nm. This suggests that the nitrogen could suppress the coarsening of M23C6 carbide once it dissolved into the M23C6 carbides. Moreover, the hardness of the10% Cr steel remained stable during aging from 27,000 h to 36,700 h, attributing to the high stability of the M23(C,N)6.

Plasma electrolytic oxidation (PEO) coatings were fabricated on the aluminum in silicate electrolyte. Microstructures and elemental compositions of these PEO coatings were examined by scanning electron microscopy (SEM) equipped with an energy-dispersive x-ray spectroscopy (EDS). Corrosion resistances of the coated samples were evaluated using the measurements of open-circuit potential (OCP), repetitive polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The results indicated that the PEO coatings not only act as a physical shield limiting the penetration of corrosive solution, but also establish an anodic location with high concentration of H+ ions and other product ions as pitting corrosion begins. With the development of pitting corrosion, the accumulation of corrosion products inside the pits and pores of the coatings decreases the corrosion process effectively.

In the current investigation, plasma electrolytic oxidation (PEO) ceramic coatings on Al are galvanostatically synthesized at various processing stages in an alkaline silicate system. The resultant coatings are systematically surveyed in terms of the following respects: the applied voltage and surface sparking evolution over the studied course of PEO are recorded by the signal acquisition system and the real time imaging, respectively; the phase constitution, the surface morphology, polished cross section of the coated specimens, the fractured cross section and coating/substrate interface of the detached coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy-dispersive X-ray spectrometer (EDS), respectively. In particular, the coatings detached by an in-house developed electrochemical way disclose the coating microstructure in a new angle, which allows the cross section and the coating/substrate interface to come clearly into focus. The microstructure evolution of the oxide ceramic coatings and the correspondences among the characteristic microstructures of the free surface, the fractured cross section and the coating/substrate interface are presented and discussed. Further, based on the present PEO coating microstructure, a model of the coating growth that evolves over time is proposed.

Coatings prepared by different electrolyte additives were investigated on AZ31 magnesium alloy by plasma electrolytic oxidation. In this study, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis were employed to assess the morphologies, chemical and phase compositions of the plasma electrolytic oxidation (PEO) coatings, respectively. Furthermore, electrochemical impedance spectroscopy was used to evaluate the corrosion behavior of the composite coating. The investigation of the effect of electrolyte additives in the base electrolyte showed that the PEO specimens exhibit different surface and cross-sectional morphologies, and phase compositions. The results showed that SiO32&minus, was conducive to the growth of the ceramic layer, and the ceramic layer developing in the electrolyte which contained AlO2&minus, showed a typical double-layer structure. The corrosion resistance of coating formed in a phosphate bath was higher than that of the coating formed in silicate bath and coating formed in an aluminate bath. Moreover, the corrosion resistance of the coating formed in the fluoride bath was the highest.

The plasma electrolytic oxidation (PEO) coatings were fabricated on AA1060 aluminum alloy at a constant current density of 4.4 A/dm2. The images of discharge sparks and voltage-time response were recorded during the PEO process. The characteristics of the two interfaces of coatings were investigated as a function of PEO processing time by using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Hundreds of coatings were detached from the substrate by an electrochemical method and ground into homogeneous powders to carry out differential scanning calorimeter (DSC) and further XRD qualitative test. In addition, matrix-flushing method was employed to quantitatively measure the content evolution of phase compositions of Al-based detached PEO coatings. The distribution rule of amorphous phases in the PEO coatings was investigated by thickness-reduction method for the first time. Based on the experiments above, gaining an insight into the formation, distribution and evolution of the amorphous and crystalline phases in the PEO process.

Evolution processes of the corrosion behavior and structural characteristics of the plasma electrolytic oxidation (PEO) coated AZ31 magnesium alloy were investigated by using scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), potentio-dynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Detached coating samples were fabricated by an electrochemical method and more details of the internal micro-structure of coatings were clearly observed on the fractured cross-section morphologies of the samples compared to general polished cross-section morphologies. Evolution mechanisms of the coating corrosion behavior in relation to the evolution of micro-structural characteristics were discussed in detail.

A CuO-Al2O3 composite coating was obtained by an AC deposition and a followed secondary MAO treatment in an acidic copper sulfate electrolyte and an alkaline sodium hexametaphosphate electrolyte. Analyzes on phase and elemental composition and microstructure showed that a continuous CuO layer was formed on the top of the original MAO coating. EIS test suggested that after a secondary MAO treatment for 1 min, the samples obtained by AC deposition for 5 min had the best corrosion resistance, because of the barrier of CuO layer to the NaCl solution.

In this study, plasma electrolytic oxidation (PEO) coatings were produced on pure aluminum in an in-house developed composite electrolyte at three current densities of 2.2 A/dm2, 4.4 A/dm2 and 8.8 A/dm2, respectively. The coatings were investigated based on the observation and measurement of the working voltage, surface microdischarges and morphologies of surface, polished cross-section, fracture cross-section and inner surface of the coatings, by using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), data acquisition module, single-lens reflex camera. Especially, an in-house developed electrochemical detachment technique of the coatings was employed to observe some details of the internal micro-structure and coating/substrate interface morphology of the coatings. It was noted that the results from the above investigations are much related to the current densities going through the PEO coatings and the different growth mechanisms of coatings at low and high current densities were proposed and discussed.

Micro-arc oxidation (MAO) coatings were prepared on Al substrate in alkaline sodium hexametaphosphate, sodium silicate and sodium aluminate electrolytes, the breakdown voltage and responsive current respectively decreased and increased with increasing the electrolyte concentration. The behavior of electrolyte during MAO processes was analyzed and discussed based on the data of the coating microstructure, elemental and phase composition, and the carrier density and impedance of the coating. The behavior can be explained by a mechanism in which anions incorporated into the coating reduced the anion vacancies, thus reducing the carrier density and improving the impedance.

The effects of corrosion products on corrosion behaviors of AZ31 magnesium alloy with a plasma electrolytic oxidation (PEO) coating were investigated under the salt spray corrosion test (SSCT). The surface morphology, cross-sectional microstructure, chemical and phase compositions of the PEO coating were determined using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis (XRD), respectively. Further, the corrosion process of the samples under the SSCT was examined in a non-aqueous electrolyte (methanol) using electrochemical impedance spectroscopy (EIS) coupled with equivalent circuit. The results show that the inner layer of the coating was destroyed firstly and the corrosion products have significant effects on the corrosion behaviors of the coating. The results above are discussed and an electrochemical corrosion model is proposed in the paper.

Plasma electrolytic oxidation (PEO) coatings were fabricated on AA1060 commercial pure aluminum and detached from the substrate by an electrochemical method. The front view and fracture cross-section morphologies of the coating/substrate (C/S) interface were observed by scanning electron microscopy (SEM). The results show that the C/S interface layer consists of inter-connected tiny globular particles. During the PEO process, the thickness of the C/S interface layer and the diameter of the inter-connected tiny globular particles maintain approximately constant values of ~ 1 μm and ~ 0.7 μm, respectively. Based on the results, a C/S interface discharge mechanism is proposed and discussed.

Ceramic coatings were performed on aluminum through plasma electrolytic oxidation (PEO) in a Na5P3O10 solution with various concentrations of NaOH. It was revealed that the concentration of NaOH affected the types of anodic films and the activity of plasma discharges. Emphatic investigation was performed on the coatings fabricated in the electrolyte with addition of 1 g L−1 NaOH, focusing on the coating microstructure evolution and coating corrosion resistance. Some coatings were detached from the substrate, showing that the oxide particles on the anodic film C/S interface underwent profile variations from hemisphere to polygon, and its interpore distance decreased over time. The formations of pores of anodic films and plasma discharge of the PEO coatings were both easy to occur around the existing pores and the existing discharge channels. Fractured cross-section showed that a pancake-like structure corresponded to a discharge channel, a cavity, and a barrier layer protrusion whose area was similar to that of the corresponding pancake-like structure. The data of potentiodynamic polarization measurements showed that the sample treated with PEO for 10 min possessed the lowest icorr value of 4.97E-8 A cm−2, the most positive Epit value of −0.63 V, and the highest Rp value of 2.66E5 Ω cm2. EIS data of 10 min sample exhibited the highest R2 value of 1.61E6 Ω cm2, demonstrating the best corrosion resistance among these samples.

In an attempt to investigate the formation rule and corrosion resistance of the plasma electrolytic oxidation (PEO) coating on crevice surface of AZ31 magnesium alloy, the crevice coatings were fabricated on the samples of irregular shapes with different values of crevice width. The value of crevice width was varied from 200 to 350 μm for investigating the effect of crevice width on the surface and cross-sectional morphology, phase composition, corrosion resistance of crevice coatings. The results indicated that the crevice coating differs markedly in morphology and corrosion resistance when the value of crevice width reaches 350 μm, in spite of all coated samples have similar phase compositions. The effect of current density and ultrasound treatment on crevice coatings thickness were also studied systematically. Studies have shown that the increase of current density and the introduction of ultrasound treatment are both favorable for the crevice coatings.

Micro-arc oxidation (MAO) in an environmentally friendly alkaline silicate electrolyte containing various concentrations of (NaPO 3 ) 6 has been used to produce oxide coatings on an AZ31 magnesium alloy. The variations of voltage, current and microdischarges with the treating time were recorded. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize microstructures and compositions of the coatings. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in the 3.5 wt.% NaCl solution were used to evaluate the corrosion behaviors of the coated samples. EIS conducted in the working electrolyte was used to test electrochemical properties of the passive films formed in the initial stage during the MAO process. The results show that (NaPO 3 ) 6 concentration significantly influences the initial passive film and hence the voltage rise rate and microdischarges. Further, the corrosion resistance of the samples decreases with increase of (NaPO 3 ) 6 concentration due to complex evolution in the microdischarges and the microstructures.

Ultrasound vibration was introduced during and after MAO process of A96061 aluminum alloy to investigate the effect mechanism of ultrasonic action on the growth of MAO coatings. The results show that during the MAO process ultrasound improved the growth behavior and the vibration-resistance performance of MAO coatings, while ultrasound post-treatment greatly increased the number of micro-flaws in the coatings and decreased the corrosion resistance of the coatings. Producing-healing circulation of micro-flaws caused by ultrasonic vibration during PEO process was thought to be the mechanism of ultrasonic action on coating growth.

It has usually been reported that the elastic stiffness of polycrystals is lower than that of the corresponding monocrystals. Recent experimental results made by Tanigaki et al. (2013) indicate that twin boundaries can improve the elastic stiffness of synthesized nano-polycrystalline diamonds. These researches imply that it may be a universal law for the twin boundary enhancing elastic stiffness. To verify this hypothesis, the elastic properties of ten face-centered-cubic (FCC) structure metals’ perfect crystals and twin crystals have been studied by using first-principles calculations. Our research findings indicated that twins cannot always enhance the elastic stiffness of FCC structure metals. These results further clarify the fact that twin boundary enhancing elastic stiffness is not a universal law.

In this paper, we investigate the microstructure and corrosion behavior of the micro-arc oxidation (MAO) coating on 6061 aluminum alloy that pre-treated by high-temperature oxidation (HTO). Microstructure, chemical and corrosion behaviors of the fabricated MAO ceramic coatings were studied by using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electrochemical corrosion tests. The results reveal that the pre-fabricated HTO film remarkably affects the formation of the MAO coating, leads to an enriched content of Mg, and decreases the compactness of the coating. The corrosion resistance of the 6061 aluminum alloy has been significantly improved by treatments of HTO, normal MAO (NMAO) and HTO pre-treated MAO (HTO-MAO), and the NMAO coating exhibits the best corrosion performance. The content of Mg in HTO pre-fabricated film is remarkedly higher than that in the substrate, which greatly influences the formation of the MAO coating.

Plasma electrolytic oxidation (PEO) coatings on AZ31 magnesium (Mg) alloy were developed using the aqueous solution with alkaline silicate and sodium hydroxide as a base electrolyte system. The effects of cerium (Ce) nitrate and lanthanum (La) nitrate additives on the voltage response, microstructure, compositions and corrosion resistance of PEO coatings were investigated by scan- ning electron microscopy (SEM), energy-dispersive spectrum (EDS), X-ray diffraction (XRD) and potentiodynamic polarization tests, etc. The results showed that Ce and La additives increased the stable voltage and compactness of the PEO coatings, while, those did not change the compositions of the PEO coatings. The corrosion resistance of the PEO coating obtained in solutions with La nitrate of 0.1 g/L was the best, followed by that with Ce nitrate of 0.1 g/L and that without additives.

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4±0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 μm. Residual stresses attributed to γ-Al2O3 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2ψ method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667±20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.

Porous carbide-derived carbons (CDCs) are synthesized from different carbide (VC, TiC, NbC) as electrode materials for electrochemical capacitors. The process of carbide–carbon transformation is investigated by observations at different carbide/CDC interfaces. It is found that the restructuring process has much influence on formation of microstructure as well as the resultant electrochemical performance. The carbon structure in the produced CDC is well in accordance with that formed at the carbide/CDC interface, indicating that the microstructure in the produced CDC is decided by re-bonding of the residual carbon atoms. It is further found that the internal stress during carbide–carbon transformation has much influence on the CDC microstructure. In addition, the microstructure in CDCs is dependent on the volumetric concentration of carbon atoms in carbide precursor. Lower volumetric concentration of carbon atoms facilitates the formation of CDC with short and curved graphene structure, which owns easily accessible pores and large specific surface area, and thus high electrochemical performance for ultracapacitor. A novel strategy that controlling microstructure of CDC through controlling the volumetric concentration of carbon atoms in carbide precursor is presented. This strategy is very effective to form designed microstructure of CDC for electrochemical applications.

Poor electrical conductivity and mechanical instability are two major obstacles to realizing high performance of MnO2 as pseudocapacitor material. The construction of unique hierarchical core-shell nanostructures, therefore, plays an important role in the efficient enhancement of the rate capacity and the stability of this material. We herein report the fabrication of a hierarchical α-MnO2 nanowires@ultrathin δ-MnO2 nanosheets core-shell nanostructure by adopting a facile and practical solution-phase technique. The novel hierarchical nanostructures are composed of ultrathin δ-MnO2 nanosheets with a few atomic layers growing well on the surface of the ultralong α-MnO2 nanowires. The first specific capacitance of hierarchical core-shell nanostructure reached 153.8 F g(-1) at the discharge current density of as high as 20 A g(-1), and the cycling stability is retained at 98.1% after 10,000 charge-discharge cycles, higher than those in the literature. The excellent rate capacity and stability of the hierarchical core-shell nanostructures can be attributed to the structural features of the two MnO2 crystals, in which a 1D α-MnO2 nanowire core provides a stable structural backbone and the ultrathin 2D δ-MnO2 nanosheet shell creates more reactive active sites. The synergistic effects of different dimensions also contribute to the superior rate capability.

The hybrid method of PEO and hot-dipping aluminum (HDA) was employed to deposit composite ceramic coatings on the surface of Q235 steel. The composition of the composite coatings was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The cross-section microstructure and micro-hardness of the treated specimens were investigated and analyzed with scanning electron microscopy (SEM) and microscopic hardness meter (MHM), respectively. The wear resistance of the ceramic coatings was investigated by a self-made rubbing wear testing machine. The results indicate that metallurgical bonding can be observed between the ceramic coatings and the steel substrate. There are many micro-pores and micro-cracks, which act as the discharge channels and result of quick and non-uniform cooling of melted sections in the plasma electrolytic oxidation ceramic coatings. The phase composition of the ceramic coatings is mainly composed of amorphous phase and crystal Al2O3 oxides. The crystal Al2O3 phase includes κ-Al2O3, θ-Al2O3 and β-Al2O3. The grain size of the κ-Al2O3 crystal is quite non-uniform. The hardness of the ceramic coatings is about HV1300 and 10 times higher than that of the Q235 substrate, which was favorable to the better wear resistance of the ceramic coatings.

This paper presents a relatively new technique for producing metal ceramic coatings on metal surfaces by a combination of plasma electrolytic deposition from a liquid medium with an electric spark discharge. The technique has some advantages compared with the separate two techniques. Particularly, the advantages are low discharge voltage and preservation of the coatings by the liquid medium. The effectiveness of the new technique is shown in this paper by coating a high speed steel, W 9 Mo 5 Cr 4 V 2 , with a metal ceramic electrode in an aqueous solution of urea. In addition, the effects of the on/off voltage pulse ratio on thickness, hardness and wear resistance of the coatings were investigated.

Plasma electrolytic oxidation (PEO) is a novel surface technique for producing ceramic coatings on valve metals and their alloys. In this paper, microstructure, temperature estimation and thermal shock resistance of the ceramic coatings formed on pure aluminum by hetero-polar pulsed current ceramic synthesizing system were investigated. Results show that the coating roughness becomes greater and the plasma discharge channel populations in the ceramic coatings decrease while the pores enlarge with PEO treatment time. In addition, the surface morphology of the ceramic coating indicates that melting and solidifying process happen alternately in the process. The results also show that the coatings have a good thermal shock resistance. Moreover, the temperature and the temperature rise rate of the plasma discharge channels were investigated, and a formula for calculating the temperature and the temperature rise rate of the plasma discharge channels at any time during the PEO process was deduced.

A novel method of surface carbonitriding modification for Q235 steel in an ethanolamine electrolyte was proposed and demonstrated in this paper. Microstructure, chemical and phase composition and properties of the carbonitriding layer were investigated. The results show that the thick carbonitriding layer can be obtained. When the substrate was processed at 150 V for 75 s, the highest thickness is about 70 μm, and the corresponding microhardness is HV750, which is 4.5 times higher than that of the substrate. The carbonitriding layers are composed of martensite, remained austenite, carbonides and nitrides with iron, such as Fe3C, Fe5C2 and ɛ-Fe2–3N. Wear test shows that the wear resistance of the sample is improved significantly compared to the substrate.

Plasma electrolytic oxidation (PEO) is a cost-effective technique that can be used to prepare ceramic coatings on metals such as Ti, Al, Mg, Nb, etc., and their alloys, but this promising technique cannot be used to modify the surface properties of steels, which are the most widely used materials in engineering. In order to prepare metallurgically bonded ceramic coatings on steels, a combined technique of arc spraying and plasma electrolytic oxidation (PEO) was adopted. In this work, metallurgically bonded ceramic coatings on steels were obtained using this method. We firstly prepared aluminum coatings on steels by arc spraying, and then obtained the metallurgically bonded ceramic coatings on aluminum coatings by PEO. The characteristics of duplex coatings were analyzed by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The corrosion and wear resistance of the ceramic coatings were also studied. The results show that, duplex Al2O3/aluminum coatings have been deposited on steel substrate after the combined treatment. The ceramic coatings are mainly composed of alpha-Al2O3, gamma-Al(2)o(3), theta-Al2O3 and some amorphous phase. The duplex coatings show favorable corrosion and wear resistance properties. The investigations indicate that the combination of arc spraying and plasma electrolytic oxidation proves a promising technique for surface modification of steels for protective purposes. (c) 2005 Elsevier B.V. All rights reserved.

The plasma electrolytic oxidation (PEO) process of 6061Al alloy was carried out under the conditions with and without the assistance of ultrasound, respectively. The effects of ultrasound on the evolution of voltage, micro-discharge, morphology and composition of PEO coatings were investigated. The results show that ultrasound can greatly decrease the dielectric breakdown voltage of the coatings, increase the number of micro-discharges while decrease their average size, promote the evolution of micro-discharges, decrease the number and the average size of residual discharge pores in the coatings after 30 min of the process, promote the homogeneous distribution of elements and the formation of α-Al2O3 and 3Al2O3⋅2SiO2 in the coatings.

A correlation method is advanced for determining the crystallization mechanism and activation energy of amorphous alloys by investigating the crystallization rate of amorphous Zr70Cu30 alloy under high pressure. The results show that this method is much closer to phase transformation reality than the Kissinger method. In principle, this method also should be applicable to kinetics of common solid-state phase transformation.