Micro arc oxidation

Brasses belong to a group of copper-based alloys with a wide variety of important applications. Traditionally, lead was a necessary alloying element in brasses due to its ability to improve machining in terms of time and quality. Additional effect of lead is a wear reduce of machining tools. The main risk of using lead-containing brasses is lead’s toxicity for humans. Various stages of producing and machining of brasses may be harmful, so certain safety regulations are normally required, which is time and
money expensive[1].
That’s why alternative technologies of producing lead-free brasses, using graphite, are of great interest. Carbon Nano-tubes (CNTs) can be considered as ideal reinforcements, due to their high specific strength, thermal, electrical and mechanical characteristics.
In the present study brass (Cu-Zn)/carbon nanotubes (CNT) composites were produced by injection of CNTs in brass using high pressure die casting method. Current
investigation demonstrates that more than 50% efficiency of direct injection of CNT in the brass has been achieved. The inserted CNTs have been partially dispersed in the metal matrix. Furthermore the friction coefficient significantly decreases with an increase of the amount of CNT content in the examined Cu-Zn brass alloy. Thus, the machinability improvement as a result of CNT performance in the examined Cu-Zn brass alloy is expected.

Orthopedic implants, such as those made of stainless steel, cobalt (Co)-based alloys and titanium (Ti) alloys, are commonly used to stabilize, protect, improve, replace or regenerate damaged musculoskeletal tissues both anatomically and functionally in millions of bone injury patients. The biggest drawback of these metallic biomaterials is their non-degradability in the body environment. Magnesium (Mg) and magnesium-based alloys are a new generation of degradable implant materials that have attracted great attention in the past 10 years. There are several advantages of magnesium-based alloys for orthopedic application over other metallic biomaterials. First, magnesium is an essential element for many biological activities, including enzymatic reactions, the formation of apatite and bone cell adsorption. Second, their mechanical properties, including density, elastic modulus and compressive yield strength, are much closer to those of natural bone, and, therefore, they can avoid the stress-shielding effect. Third, magnesium alloys can eliminate the necessity of a second surgery to remove permanent bone implants. Recent results show that alloying of magnesium with aluminum (Al), zinc (Zn), calcium (Ca), zirconium (Zr), yttrium (Y) and rare-earth elements can significantly improve its corrosion resistance and mechanical strength. This paper reviews and compares the mechanical properties, corrosion resistance and biocompatibility of currently researched magnesium-based alloys for use in medical implant applications.

MgO/ZnO composite coatings were successfully prepared on AZ91 Mg alloy by plasma electrolytic oxidation (PEO) method using electrolytes containing ZnO nanoparticles (NPs) to extend their biomedical applications. The effect of the concentration of 0 to 4.5 g·L −1 ZnO NPs in phosphate-based electrolyte on the microstructure, composition, physical features, corrosion and biodegradation properties of coatings was investigated. Observing the microstructure through field emission scanning electron microscopy (FESEM) confirmed that ZnO NPs were well up-taken in the coating structure with crater-like morphology and, they were mostly accumulated near the pores. As ZnO NPs concentration increased, more particles were incorporated in the coating; however, porosity, thickness and surface roughness reduced. The evaluation of the electrochemical behavior of specimens using potentiodynamic polarization test revealed that the polarization resistance of the samples increased from 9.26 to 683.2 kΩ·cm 2 by adding 4.5 g·L −1 ZnO NPs. The study of corrosion mechanism by identifying the coating features using electrochemical impedance spectroscopy (EIS) indicated that the compacting of the coating and the difficulty of the penetration path of corrosive ions between the coating layers due to the presence of ZnO NPs had a more dominant effect relative to thickness reduction. Conducting the bioactivity test by immersion of coatings in simulated body fluid (SBF) solution for 14 days showed the higher growth of calcium phosphate layer formed on the sample as the concentration of ZnO NPs increases. In addition, the changes in weight loss and volume of hydrogen evolution were much less, and the mechanism of these changes was presented.

Biodegradable magnesium (Mg) alloys have been widely used in fabrication of biomedical orthopedic implants owing to their similar characteristics to natural bone. In order to create a strong connection to the bone and to prevent inflammation, these implants should have a high corrosion resistance in physiological environment. In this study, Graphene oxide (GO) layer was produced on a plasma electrolytic oxidation (PEO) coating of AZ91 Mg alloy by electrophoretic deposition (EPD) process. The field emission scanning electron microscopy (FE-SEM) micrographs of the coating surfaces and cross sections showed that PEO coating had porous structure which considerably changed after EPD treatment and its micropores and microcracks were sealed by GO particles. Also, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) results confirmed the formation of GO layers on MgO coating after PEO/EPD process. The corrosion behavior was studied by conducting potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in simulated body fluid (SBF) solution. Potentiodynamic tafel curve measurements demonstrated that the corrosion current density of the MgO/GO coating decreased by 56 and 708 times compared to PEO coating and bare substrate, respectively. Moreover, the EIS results indicated that the value of |Z| f→0 of the MgO/GO coating (1.64×10 6 Ώ.cm 2) was slightly higher than PEO coating (8.21×10 4 Ώ.cm 2), attributed to the formation of a GO film as the top layer preventing infiltration of aggressive solution into the AZ91 substrate.

In this study, pre anodized Al 6061 alloy was coated with protective ceramic coatings using micro-arc oxidation process (MAO). MAO electrolyte was modified using natural additives of rice hushes ash (RHA) fired at 800 ͦ C and porcelanite rocks fired at 700 ͦ C. The surface morphology, phase content, structure, and element distribution of the coatings were investigated by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and atomic force microscopy. Results showed that the samples coatings contained γ-alumina, and their thickness and hardness increased by the increasing of deposition time. The research demonstrates that a relatively hard, thick and uniform coatings with good wear resistance, can successfully be deposited on pre anodized Al alloy using natural additives of rice hushes ash (RHA) and porcelanite rocks containing MAO electrolytes as natural additives. The results proved that the pre anodized surfaces promoted the MAO coating in providing the higher hardness in comparison to untreated surfaces.

This paper aims at presenting preliminary findings of TSAO-tech project, focused on steel-based components coated with thermal spray aluminum (TSA) and treated by Micro-Arc Oxidation (MAO) to obtain alumina coatings. The MAO process, which is also known as plasma electrolytic oxidation, spark anodization or micro-arc discharge oxidation, is a combination of electrochemical oxidation and high voltage spark treatment. As a result, a protective layer which has excellent adhesive, strength, friction, corrosion, wear, electrical and thermal properties is obtained. The received technical benefits from TSA coatings treated by MAO allow to increase items service life, reduce maintenance costs and find new applications for TSA in fields such as marine industry and chemical industry.

Protective coatings are formed on different magnesium-based alloys (Mg-Mn-Ce, Mg-Zn-Zr, Mg-Al-Zn-Mn, Mg-Zn-Zr-Y, and Mg-Zr-Nd) by plasma electrolytic oxidation. Electrochemical and mechanical properties of the coatings are studied, as well as their chemical and phase compositions and structures. Analysis of the data obtained revealed the reasons for the differences in the corrosion and mechanical characteristics between plasma electrolytic layers formed on different magnesium alloys used in aviation and space engineering.

Keywords: Monocrystalline silicon Plasma electrolytic oxidation Silicate electrolyte Boric acid A B S T R A C T The feasibility of preparing oxide layer on a monocrystalline silicon (mc-Si) using the plasma electrolytic oxidation (PEO) process was investigated in this study and the influence of adding boric acid to the silicate based electrolyte on the formation and the properties of the oxide layer was evaluated. The morphology, chemical composition and phase structure of the layers were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), grazing incidence X-ray diffractometry (GIXRD) and transmission electron microscopy (TEM) techniques. The optical and electrical properties of the grown layers were assessed by ultraviolet-visible spectroscopy (UV-Vis), photoluminescence spectroscopy (PL) and current-voltage measurement methods. The results revealed that an amorphous silicon oxide (SiO 2) layer with a crater-like morphology was formed on the mc-Si substrate in the silicate based elec-trolyte. The addition of boric acid to the electrolyte led to dramatic arcing, stable layer formation conditions, and improved feature quality. The presence of BO 3 3− anions in the electrolyte accelerated the rate of growth, increased the layer surface porosity, and doped the SiO 2 structure with boron cations. As a result of these changes, the optical absorbance and photoluminescence emission intensity of the doped oxide layer was enhanced in both ultraviolet and visible regions, as well as the Urbach tail widened, which is declining the band gap energy. In addition, despite the increased surface electrical resistance, the current gain was also increased significantly.

In this study, pre anodized Al 6061 alloy was coated with protective ceramic coatings using micro-arc oxidation process (MAO). MAO electrolyte was modified using natural additives of rice hushes ash (RHA) fired at 800 ͦ C and porcelanite rocks fired at 700 ͦ C. The surface morphology, phase content, structure, and element distribution of the coatings were investigated by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and atomic force microscopy. Results showed that the samples coatings contained γ-alumina, and their thickness and hardness increased by the increasing of deposition time. The research demonstrates that a relatively hard, thick and uniform coatings with good wear resistance, can successfully be deposited on pre anodized Al alloy using natural additives of rice hushes ash (RHA) and porcelanite rocks containing MAO electrolytes as natural additives. The results proved that the pre anodized surfaces promoted the MAO coating in providing the higher hardness in comparison to untreated surfaces.

In this work, the morphology, phase composition, and corrosion properties of microarc oxidized (MAO) gas tungsten arc (GTA) weldments of AZ31 alloy were investigated. Autogenous gas tungsten arc welds were made as full penetration bead-on-plate welding under the alternating-current mode. A uniform oxide layer was developed on the surface of the specimens with MAO treatment in silicate-based alkaline electrolytes for different oxidation times. The corrosion behavior of the samples was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. The oxide film improved the corrosion resistance substantially compared to the uncoated specimens. The sample coated for 10 min exhibited better corrosion properties. The corrosion resistance of the coatings was concluded to strongly depend on the morphology, whereas the phase composition and thickness were concluded to only slightly affect the corrosion resistance.

In this research, porous plasma electrolyte oxidation (PEO) coatings were prepared on AZ31 magnesium alloys with the aim of investigating how PEO competitive mechanism affects the coating properties. Thickness of the coated layer, surface morphology, phase structure and quantitative information about porosity were analyzed by FE-SEM, XRD and MATLAB software. The result showed that PEO competitive mechanism was influenced by process parameters such as time, current density, conductivity and breaking voltage. It was concluded that the competition between dissolution rate of magnesium alloy and ceramic coating formation, determines the pore size, thickness and porosity of coating, which are of great importance in bone cell interlocking after implantation. Moreover, various phosphate salt solutions were studied in terms of conductivity. It was concluded that, the degree of phosphate hydration and hydrogenation affects the conductivity and pH of electrolyte. Also, hydrogenated phosphate ions, caused the formation of PEO coating layer including non-adhesive compound which prevented plasma sparking.

The micro arc oxidation (MAO) technique is being increasingly recognized as a novel and ecofriendly means of depositing dense ceramic oxide coatings on Al and its alloys. In the present study, the deposition kinetics, surface roughness, morphology, phase distribution and the microhardness of the MAO coatings deposited on ten different commercially available Al substrates having widely differing chemical composition has been investigated. Further, the tribological properties of the coatings obtained on different Al alloys in comparison with the bare substrates have also been evaluated using dry sand abrasion, solid-particle erosion and pin-on-disc dry sliding wear tests. The results clearly demonstrate that the alloying elements added to the Al substrate substantially influence the MAO coating deposition kinetics and coating properties. In the case of Al-Si alloys, the coating deposition kinetics is non-linear and the Al6Si2O13 (mullite) is observed to form. With increasing Si content, the corresponding mullite phase also increases. Increasing mullite content in the coating adversely affects the tribological performance. Excepting Al-Si alloys, all other alloys investigated including commercial purity Al exhibit linear coating deposition kinetics. Of all the alloys investigated, Al-Li alloy exhibits the highest coating deposition rate and the 6061 T6 Al alloy exhibits the best coating properties.

Biomimetic apatite coatings on micro-arc oxidized titania films were investigated and their apatite-inducing ability was evaluated in a simulated body fluid (1.0SBF) as well as in a 1.5 times concentrated SBF (1.5SBF). Titania-based films on titanium were prepared by micro-arc ...

rGO/SiO 2 composite coating was successfully prepared by plasma electrolyte oxidation (PEO) process on monocrystalline silicon (mc-Si) substrate. Investigating the effect of rGO incorporation into the SiO 2 coating revealed that the addition of rGO leads to a significant increase in the photo-trapping ability due to the high specific surface area and excellent electron transfer efficiency. The PL intensity of the composite sample was found to decrease, which signified the suspension of the electron-hole pairs' recombination. As a result, the photocurrent gain of the composite coating enhanced about 5.5 times. Likewise, the time-response switching featured an over twofold increase for the rGO/SiO 2 coating, impressively.

The micro arc oxidation (MAO) process has been applied to produce ceramic oxide coating on Ti-6Al-4V alloy. The MAO process was carried out at the symmetric bipolar square pulse in electrolyte containing Na 2 CO 3 and Na 2 SiO 3. The effect of current frequency on the surface morphology, the chemical and the phase compositions as well as the corrosion resistance was examined. Morphology and cross-sectional investigation by electron microscopy evaluated more compacted and less porous coating produced by high current frequency (1000 Hz). This alloy also exhibited a high corrosion resistance in comparison with the untreated alloy. Additionally, the alloy subjected to MAO treatment by a current frequency of 1000 Hz showed a higher corrosion resistance in comparison with alloys obtained by lower current frequencies. This behavior was attributed to more compacted and less porous morphology of the coating.

Modified oxide layer was successfully prepared on AZ91 magnesium alloy by plasma electrolytic oxidation (PEO) using phosphate electrolyte containing calcium fluoride (CaF 2). Evaluating the corrosion behavior of the oxidized AZ91 magnesium alloy by potentiodynamic polarization in simulated body fluid (SBF) solution indicated that addition of CaF 2 to electrolyte leads to considerable decrease in corrosion rate caused by surface porosity, oxide layer thickness, and formation of MgF 2 phase. Electrochemical impedance spectroscopy (EIS) revealed that the resistance of the outer porous and the inner barrier parts of the oxide layer increased by 3 and 41 times, respectively. Presence of biological calcium ion along with fluorine and phosphorous ions in the oxide layer composition created a higher driving force for nucle-ation and growth of bioactive layer by decreasing the contact angle with SBF solution.

The current study investigates the corrosion
properties of Micro Arc Oxidized (MAO) AZ31 alloy and its
weldments. Autogenous full penetration bead-on-plate GTA
welds were made under alternating current mode. Uniform
oxide layer was developed on the surface of the specimens
with MAO treatment in silicate based alkaline electrolyte for
different times. The corrosion behavior of the samples was
evaluated by potentio dynamic polarization studies in 3.5 wt%
NaCl solution. The MAO layer improved the corrosion
resistance significantly compared to the uncoated specimens
irrespective of the base microstructure. Base metal coated for
20 min showed better corrosion resistance, whereas welds
coated for 10 min exhibited better corrosion resistance. It was
observed that corrosion resistance of the coatings strongly
depends on morphological characteristics, not on phase
composition.

Brasses belong to a group of copper-based alloys with a wide variety of important applications. Traditionally, lead was a necessary alloying element in brasses due to its ability to improve machining in terms of time and quality. Additional effect of lead is a wear reduce of machining tools. The main risk of using lead-containing brasses is lead’s toxicity for humans. Various stages of producing and machining of brasses may be harmful, so certain safety regulations are normally required, which is time and money expensive[1]. That’s why alternative technologies of producing lead-free brasses, using graphite, are of great interest. Carbon Nano-tubes (CNTs) can be considered as ideal reinforcements, due to their high specific strength, thermal, electrical and mechanical characteristics. In the present study brass (Cu-Zn)/carbon nanotubes (CNT) composites were produced by injection of CNTs in brass using high pressure die casting method. Current investigation demonstrates that more than...