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TC11 alloy is an important high temperate Ti alloy. Its laser in-situ alloying by powder bed fusion-laser beam (PBF-LB) has been explored in this study. Results show that it is feasible to print the TC11 alloy using elemental powders rather than pre-alloyed powder, in terms of high density and good combination of strength and ductility at both room and elevated temperatures, along with minor loss of composing elements. Interestingly, it is noticed that an unusual nanocrystalline microstructure has formed due to the use of ZrH2 powder feedstock, partially explaining the reason for the good mechanical properties achieved. Finite element analysis has been employed to understand the in-situ alloying. Furthermore, a post processing by micro-arc oxidation (MAO) has been employed to the alloy, aiming to enhance its high-temperature oxidation resistance. The results make an implication that hydrides such as ZrH2 may hold the promise to develop nanosized, advanced Ti materials through laser in-situ alloying, and MAO can be considered for PBF-LB prepared TC11 alloy. [ABSTRACT FROM AUTHOR]

The technique of micro arc oxidation (MAO) uses arc discharge and high-voltage breakdown to produce a ceramic layer on valve metal surfaces. However, the common method of MAO requires immersing the workpiece in an electrolyte solution, which can result in elevated temperatures due to the arc discharge, thus negatively affecting the coating's quality and performance. This article investigates the influence of electrolyte temperature on the performance of MAO ceramic coatings, with the assistance of a robotic arm enabling valve metal reaction without immersion in the electrolyte, and precise control of electrolyte temperature through a MAO temperature monitoring system. Various techniques, such as scanning electron microscopy (SEM), hardness testing, electrochemical corrosion experiments, and friction-wear experiments, were utilized to characterize the performance of the prepared coating. The results indicate a nonlinear correlation between the temperature of the electrolyte and the thickness and hardness of the ceramic coating. The corrosion and wear resistance of the MAO ceramic coatings initially improve with increasing electrolyte temperature but eventually deteriorate. At an electrolyte temperature of 40 °C, the MAO ceramic coating exhibits the optimal corrosion and wear resistance. The variation in electrolyte temperature affects the reactivity of the electrolyte ions, leading to changes in the morphology and properties of the resulting MAO ceramic coating. These findings offer valuable insights into the interaction mechanism between electrolyte temperature and the properties of the resulting MAO ceramic coating. This is of great significance in optimizing the MAO process for specific applications and improving the overall performance of ceramic coatings. [ABSTRACT FROM AUTHOR]

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In recent years, magnesium (Mg) has evolved as a salient material, in affiliation with electroless nickel (Ni) coating, which have found applications in automobiles, aerospace and confederate fields attributing to its excellent inherent weight sensitive properties. However, being acknowledged for its remarkable auxiliary properties like flexible machining, appreciable weight sensitivity and ability to be patently diecast into mesh constructs, magnesium is prejudiced by aeronautical standards predominantly for its inferior corrosion resistance properties. In this sense, electroless nickel plating on magnesium and its alloys has been suggested to extricate it from corrosion problem and make it more competitive in industrial and defence applications. Autocatalytic fixation of metal ions onto respective substrates accrues and alters their mechanical, electrochemical and tribological properties, destitute of any electric current aid. This proficiently identified technique is prosecuted with the assistance of a series of sequenced operations involving a prior pretreatment, which corresponds to the chemical cleaning of the substrate surface; electroless coating; and a later activation process which is a mild etching of the electroless coated surface. The susceptibility of magnesium to this methodology has advanced and propagated its exercise and applicability in aircraft, satellites and allied aeronautical fields. Contemporarily, researchers have proposed various eco-friendly and modified duplex and composite coatings which have transmuted properties of these appendages by tailoring alloy compositions and reagents employed. This review article systematically colligates various considerations and evaluations on electroless nickel applications of magnesium and its alloys and explicates how it anchors its practice in the respective domains. Furthermore, a comprehensive analysis is devised based on the pre-existing treatment methods for accomplishing the same. [ABSTRACT FROM AUTHOR]

Plasma Electrolytic Oxidation (PEO) known also as Micro Arc Oxidation (MAO) process is widely used to fabricate porous coatings on titanium and its alloys mainly in water- and acid-based solutions to different applications, e.g. in biomaterials, catalysts, and sensors. In the present paper, the SEM, EDS, and XPS results of porous coatings obtained by PEO treatment on titanium in electrolytes based on concentrated phosphoric H3PO4 acid with calcium nitrate tetrahydrate Ca(NO3)2·4H2O, or magnesium nitrate hexahydrate Mg(NO3)2·6H2O, or zinc nitrate hexahydrate Zn(NO3)2·6H2O for 3 minutes at 200 Vpp (peak to peak) with frequency of 50 Hz, are presented. Based on EDS results, the Ca/P, Mg/P, and Zn/P ratios, which equal to 0.95, 0.176, and 0.231, respectively, were found out. The XPS studies of the top 10 nm of the porous layer clearly indicate that it contains mainly phosphates (PO4 3- and/or HPO4 2- and/or H2PO4 -, and/or P2O7 4-) with titanium (Ti4+) and calcium (Ca2+) or magnesium (Mg2+), or zinc (Zn2+). [ABSTRACT FROM AUTHOR]

The in vitro and in vivo degradation behaviour and biocompatibility of a Mg-Mn-Zn alloy with MAO coating and MAO/PLLA composite coating were studied. The in vitro degradation behaviour was studied by investigating electrochemical behaviour and observing surface morphology for up to 12 weeks and the in vivo degradation behaviour and osteogenic effect were studied by implanting the samples in the mandibles for up to 16 weeks. Both in vitro and in vivo degradation results demonstrated the MAO/PLLA composite coating effectively reduced the degradation rate Mg-Mn-Zn alloy in comparison with MAO coated alloy, while localized degradation was the main degradation form for the coated Mg alloys. In vivo implantation analysis results clearly showed that the MAO/PLLA coated sample exhibited less local osteogenic defects, less bone cavities and less local inflammatory reaction than MAO coated sample. However, more attentions should be paid on the osteogenic defects around the localized corrosion region of the MAO/PLLA coated sample. It was suggested that MAO/PLLA might be an effective coating for the bone implant application of magnesium alloy. • PLLA polymer blocks MAO oxidation hole, hinders charge transfer and slows down corrosion process. • Samples with lower corrosion rate had stronger bone growth promoting ability. • Localized corrosion is the main corrosion form of the MAO/PLLA composite coating samples. • The rapid accumulation of local corrosion products and alkalization led to surrounding cavity bone non-union. • Tightly wrapped bone tissue surrounding the implant protected the erosion of body fluid and delayed the subsequent degradation process. [ABSTRACT FROM AUTHOR]

The aim of the paper is to study and determine the effect of voltage increasing from 500 up to 650 VDC on chemical and electrochemical properties of the obtained porous coatings with plasma electrolytic oxidation (PEO) processes, known also as micro arc oxidation (MAO). In the present paper, the chemical and electrochemical characterization of porous phosphate coatings enriched with magnesium or zinc on commercially pure (CP) Titanium Grade 2 under DC-PEO obtained in electrolytes based on concentrated 85% analytically pure H3PO4 (98 g/mole) acid with additions of 500 g·L-1 of zinc nitrate Zn(NO3)2·6H2O or magnesium nitrate Mg(NO3)2·6H2O, are described. These materials were characterized using scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectroscopy (GDOES). It was found that the voltage of PEO process has influence on the chemical composition and thickness of the obtained porous coatings as well as on their electrochemical behavior. The higher the potential of PEO treatment, the higher the amount of zinc-to-phosphorus ratio for zinc enriched coatings was obtained, whereas in magnesium enriched coatings, the average amount of magnesium detected in PEO coating is approximately independent of the PEO voltages. Based on XPS studies, it was found out that most likely the top 10 nm of porous coatings is constructed of titanium (Ti4+), magnesium (Mg2+), zinc (Zn2+), and phosphates PO43- and/or HPO42- and/or H2PO4-and/or P2O7 4-. On the basis of GDOES studies, a four-sub-layer model of PEO coatings is proposed. Analysis of the potentiodynamic corrosion curves allowed to conclude that the best electrochemical repeatability was noted for magnesium and zinc enriched coatings obtained at 575 VDC. [ABSTRACT FROM AUTHOR]

The hydroxyapatite (HA); a bioactive and biocompatible; was formed on steel by electro-spark deposition (ESD) and micro-arc oxidation (MAO). At the first stage, Ti6Al4V alloy was coated on steel by ESD method under argon atmosphere. And then, the HA-based ceramic coatings were directly fabricated on ESD coated surface by MAO in an aqueous electrolyte containing calcium acetate and β-calcium glycerophosphate-based electrolyte at 30 min. The phase structure, surface and cross-sectional morphology, surface topography and roughness, wettability, surface and cross-sectional elemental composition and functional groups of the coatings were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), surface profilometer, contact angle goniometer (CAG), energy dispersive spectroscopy (EDX-Mapping) and Fourier transformed infrared spectroscopy (FTIR), respectively. The highly crystalline HA structure was detected on ESD + MAO surface. The HA-based surface was rough and porous due to the existence of micro discharge channels through MAO. The elements such as Ca and P in the structure of HA were homogeneously distributed over the whole surface. The HA-based duplex coating had a low contact angle indicated a hydrophilic character due to the existence of porous and rough structure on the surface. The bioactivity of HA-based coatings was carried out by immersion test in simulated body fluid (SBF) at body temperatures up to 14 days. After 14 days, the HA-based surface was uniformly covered by secondary apatite structure. The HA-based coating on steel significantly contributed improving bioactivity. [ABSTRACT FROM AUTHOR]

In the paper, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Glow Discharge Optical Emission Spectroscopy (GDOES) analyses of calcium- and phosphorus-enriched coatings obtained on commercial purity (CP) Titanium Grade 2 by plasma electrolytic oxidation (PEO), known also as micro arc oxidation (MAO), in electrolytes based on concentrated phosphoric acid with calcium nitrate tetrahydrate, are presented. The preliminary studies were performed in electrolytes containing 10, 300, and 600 g/L of calcium nitrate tetrahydrate, whereas for the main research the solution contained 500 g/L of the same hydrated salt. It was found that non-porous coatings, with very small amounts of calcium and phosphorus in them, were formed in the solution with 10 g/L Ca(NO3)2·4H2O, whereas the other coatings, fabricated in the consecutive electrolytes containing from 300 up to 650 g/L Ca(NO3)2·4H2O, were porous. Based on the GDOES data, it was also found that the obtained porous PEO coating may be divided into three sub-layers: the first, top, porous layer was the thinnest; the second, semi-porous layer was about 12 times thicker than the first; and the third, transition sub-layer was about 10 times thicker than the first. Based on the recorded XPS spectra, it was possible to state that the top 10-nm layer of porous PEO coatings included chemical compounds containing titanium (Ti4+), calcium (Ca2+), as well as phosphorus and oxygen (PO43- and/or HPO42- and/or H2PO4-, and/or P2O74-). [ABSTRACT FROM AUTHOR]

In this paper, a preparation method and characteristics of porous coatings enriched in copper distributed in the whole volume on a ternary Ti-Nb-Zr alloy biomaterial obtained by plasma electrolytic oxidation (PEO) in an electrolyte containing HPO within Cu(NO) at potentials of 180 and 450 V are presented. It has been shown that the PEO potential has impact on the thickness of the coatings, i.e., the higher the potential used, the thicker the coating obtained. Using XPS study, it was shown that copper inside the coating appears as Cu and Cu ions, while titanium, niobium, and zirconium appear as Ti, Nb, and Zr (x ≤ 2), respectively. It was also found that the roughness of PEO coating formed at 450 V is higher than the one obtained at 180 V, and it is well correlated with bigger pores after the PEO treatment. Additionally, in this paper two PEO coating models composed of three sub-layers are presented. The thickness of the outer top porous sub-layer obtained after PEO oxidation at both 180 and 450 V equals to about 2 μm, while the semi-porous as well as transition sub-layers are thicker after PEO processing at 450 V (5 μm) than those obtained at 180 V (4 μm thick). The creation of the top porous and transition compact sub-layer of PEO coating may be explained by switch-on and switch-off of the PEO potential, while the middle and semi-porous sub-layers are most likely formed during the stable voltage conditions of PEO treatment. [ABSTRACT FROM AUTHOR]

In the paper, the effect of voltage increase (from 500 VDC up to 650 VDC) on the structure and chemical composition of the porous coating on titanium made by Plasma Electrolytic Oxidation is presented. Phosphates-based coatings enriched with calcium, magnesium, zinc, and copper in electrolyte based on 1 L of 85% concentrated H3PO4, with additions of Ca(NO3)2·4H2O, and Mg(NO3)2∙6H2O, and Zn(NO3)2∙6H2O, and Cu(NO3)2∙3H2O, are described. The morphology and chemical and phase composition are evaluated using SEM, EDS, XRD, XPS, GDOES, and CLSM. Based on these analyses, it was found that PEO coatings are porous and enriched with calcium, magnesium, zinc and copper. They consist mainly of the amorphous phase, which is more visible for higher voltages; this is correlated with an increase in the total PEO coating thickness (the higher the voltage, the thicker the PEO coating). However, for 650 VDC, an amorphous phase and titanium substrate were also recorded, with a signal from Ti2P2O7 crystalline that was not observed for lower voltages. It was also found that all obtained coatings may be divided into three sub-layers, i.e., porous, semiporous, and transitional.

The SEM and EDS study results of coatings obtained on titanium by Plasma Electrolytic Oxidation (PEO) in the electrolytes containing of 600 g copper nitrate in 1 liter of concentrated phosphoric acid at 450 V for 1 and 3 minutes, are presented. The obtained coatings are porous and consist mainly of phosphorus within titanium and copper. It was found that the time of PEO oxidation has impact on the chemical composition of the coatings. The longer time of PEO treatment, the higher amount of copper inside coating. The PEO oxidation of titanium for 1 minute has resulted in the creation of coating, on which 3 phases where found, which contained up to 13.4 wt% (9 at%) of copper inside the phosphate structure. In case of 1 minute PEO treatment of titanium, the 2 phases were found, which contained up to 13 wt% (8 at%) of copper inside the phosphate structure. The copper-tophosphorus ratios after 1 minute processing belong to the range from 0.28 by wt% (0.14 by at%) to 0.47 by wt% (0.23 by at%), while after 3 minutes the same ratios belong to the range from 0.27 by wt% (0.13 by at%) to 0.35 by wt% (0.17 by at%). In summary, it should be stated that the higher amounts of phosphorus and copper were recorded on titanium after PEO oxidation for 3 minutes than these after 1 minute. [ABSTRACT FROM AUTHOR]

In the paper, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) results of the Ti6Al4V alloy treated by a novel plasma electrolytic oxidation (PEO) (micro arc oxidation) in the electrolyte containing concentrated phosphoric acid and copper nitrate are presented. The PEO treatment was performed at the voltage of 450 ± 10 V. The main problem to solve under the experiments was to obtain a porous surface layer composed mainly of titanium phosphates within the copper ions. The performed study has shown that the amount of copper nitrate in 85 % concentrated phosphoric acid should be not less than 1.60 mol/L. The best result in the case of copper (4.3 ± 0.6 wt%) and phosphorus (19.9 ± 0.5 wt%) contents in the surface layer was obtained after the PEO treatment in electrolyte with the highest amount of copper nitrate used, i.e., in 3.20 mol/L of Cu(NO) in HPO. Concerning the Ti6Al4V alloy for the use as biomaterial, an interesting characteristic and a great advantage obtained from the proposed PEO treatment is eliminating vanadium and a considerable diminishing of aluminum from the surface coating. Two elements forming Ti6Al4V alloy, vanadium, and aluminum are detrimental for human body. After implantation, vanadium leaking from this biomaterial reveals the carcinogenic effects whereas aluminum has an impact on acceleration and stimulation of Alzheimer's disease. Separation and isolation of the human tissue from the matrix is a crucial task of researchers. The proposed new PEO process fulfills this requirement and may result in great improvement of the biomedical surface characteristics. [ABSTRACT FROM AUTHOR]

In the paper, the Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) results of the surface layer formed on pure titanium after plasma electrolytic oxidation (micro arc oxidation) at the voltage of 450 V are shown. As an electrolyte, the mixture of copper nitrate Cu(NO3)2 (10-600 g/L) in concentrated phosphoric acid H3PO4 (98 g/mol) was used. The thickness of the obtained porous surface layer equals about 10 µm, and it consists mainly of titanium phosphates and oxygen with embedded copper ions as a bactericidal agent. The maximum percent of copper in the PEO surface layer was equal to 12.2 ± 0.7 wt % (7.6 ± 0.5 at %), which is the best result that the authors obtained. The top surface layer of all obtained plasma electrolytic oxidation (PEO) coatings consisted most likely mainly of Ti3(PO4)4⋅nH3PO4 and Cu3(PO4)2⋅nH3PO4 with a small addition of CuP2, CuO and Cu2O. [ABSTRACT FROM AUTHOR]

The aim of the paper is to study and determine the effect of voltage increasing from 500 up to 650 VDC on chemical and electrochemical properties of the obtained porous coatings with plasma electrolytic oxidation (PEO) processes, known also as micro arc oxidation (MAO). In the present paper, the chemical and electrochemical characterization of porous phosphate coatings enriched with magnesium or zinc on commercially pure (CP) Titanium Grade 2 under DC-PEO obtained in electrolytes based on concentrated 85% analytically pure H3PO4 (98 g/mole) acid with additions of 500 g·L−1 of zinc nitrate Zn(NO3)2∙6H2O or magnesium nitrate Mg(NO3)2∙6H2O, are described. These materials were characterized using scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectroscopy (GDOES). It was found that the voltage of PEO process has influence on the chemical composition and thickness of the obtained porous coatings as well as on their electrochemical behavior. The higher the potential of PEO treatment, the higher the amount of zinc-to-phosphorus ratio for zinc enriched coatings was obtained, whereas in magnesium enriched coatings, the average amount of magnesium detected in PEO coating is approximately independent of the PEO voltages. Based on XPS studies, it was found out that most likely the top 10 nm of porous coatings is constructed of titanium (Ti4+), magnesium (Mg2+), zinc (Zn2+), and phosphates PO43− and/or HPO42− and/or H2PO4− and/or P2O74−. On the basis of GDOES studies, a four-sub-layer model of PEO coatings is proposed. Analysis of the potentiodynamic corrosion curves allowed to conclude that the best electrochemical repeatability was noted for magnesium and zinc enriched coatings obtained at 575 VDC.

In the paper, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Glow Discharge Optical Emission Spectroscopy (GDOES) analyses of calcium- and phosphorus-enriched coatings obtained on commercial purity (CP) Titanium Grade 2 by plasma electrolytic oxidation (PEO), known also as micro arc oxidation (MAO), in electrolytes based on concentrated phosphoric acid with calcium nitrate tetrahydrate, are presented. The preliminary studies were performed in electrolytes containing 10, 300, and 600 g/L of calcium nitrate tetrahydrate, whereas for the main research the solution contained 500 g/L of the same hydrated salt. It was found that non-porous coatings, with very small amounts of calcium and phosphorus in them, were formed in the solution with 10 g/L Ca(NO3)2·4H2O, whereas the other coatings, fabricated in the consecutive electrolytes containing from 300 up to 650 g/L Ca(NO3)2·4H2O, were porous. Based on the GDOES data, it was also found that the obtained porous PEO coating may be divided into three sub-layers: the first, top, porous layer was the thinnest; the second, semi-porous layer was about 12 times thicker than the first; and the third, transition sub-layer was about 10 times thicker than the first. Based on the recorded XPS spectra, it was possible to state that the top 10-nm layer of porous PEO coatings included chemical compounds containing titanium (Ti4+), calcium (Ca2+), as well as phosphorus and oxygen (PO43− and/or HPO42− and/or H2PO4−, and/or P2O74−).

The oxide coatings with thicknesses of 8 μm, 10 μm, and 15 μm were prepared on 7475 aluminum alloy with micro arc oxidation (MAO) by controlling MAO time, the fatigue limits of original and MAO samples were contrastively measured by the Roccati method. The surface-interface morphologies, fracture morphologies, surface phases, and residual stresses of MAO coating were analyzed with a scanning electron microscopy (SEM), X-ray diffractometer (XRD) and XRD stress tester, respectively. The results show that fatigue limits of the MAO samples decreases as the coating thickness increasing. The fatigue limit of MAO sample with thickness of 8 μm, 10 μm, and 15 μm decreases by 6.48%, 8.33%, and 11.11%, respectively, compared with the original sample. The residual stress and defects introduced by MAO were the main factors of decreasing fatigue limits. [ABSTRACT FROM AUTHOR]

Abstracts: The commercial pure magnesium was coated by micro arc oxidation method in different aqueous solution, containing sodium silicate and sodium phosphate. Micro arc oxidation process was carried out at 0.060A/cm2, 0.085A/cm2 and 0.140A/cm2 current densities for 30min. The thickness, phase composition, morphology, hardness, adhesion strength and wear resistance of coatings were analyzed by eddy current, X-ray diffraction (XRD), scanning electron microscope (SEM), micro hardness tester, scratch tester and ball-on disk tribometer, respectively. The average thicknesses of the micro arc oxidized coatings ranged from 27 to 48μm for sodium silicate solution and from 45 to 75μm for sodium phosphate solution. The dominant phases formed on the pure magnesium were found to be a mixture of spinel Mg2SiO4 (Forsterite) and MgO (Periclase) for sodium silicate solution and Mg3(PO4)2 (Farringtonite) and MgO (Periclase) for sodium phosphate solution. The average hardnesses of the micro arc oxidized coatings were between 260HV and 470HV for sodium silicate solution and between 175HV and 260HV for sodium phosphate solution. Adhesion strengths and wear resistances of coatings produced in sodium silicate solution were higher than those of the ones in sodium phosphate solution due to high hardness of coatings produced in sodium silicate solution. [Copyright &y& Elsevier]

Magnesium alloys are used in the motorsport and aerospace fields because of their high specific strength. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating, are necessary when they are used in humid or corrosive environments. The present study aimed at evaluating the effect of plasma electrolytic oxidation (PEO), followed by the deposition of a polymeric layer by powder coating, on the rotating bending fatigue behaviour of the wrought magnesium alloy ZK60A-T5. The specimens were extracted from forged wheels of racing motorbikes and were PEO treated and powder coated. Microstructural characterization was carried out by optical (OM) and scanning electron microscopy (SEM) to analyse both the bulk material and the multilayer, consisting of the anodic oxide interlayer with the powder coating top layer (about 40 µm total thickness). Rotating bending fatigue tests were carried out to obtain the S–N curve of PEO-treated specimens. The results of the rotating bending tests evidenced fatigue strength equal to 104 MPa at 106 cycles and 90 MPa at 107 cycles. The results of the investigation pointed out that PEO led to a reduction in fatigue strength between 14% and 17% in comparison to the untreated alloy. Fracture surface analyses of the fatigue specimens, carried out by SEM and by 3D digital microscopy, highlighted multiple crack initiation sites at the interface between the PEO layer and substrate, induced by the concurrent effects of coating defects, local tensile stresses in the substrate, and increased roughness at the substrate–coating interface. [ABSTRACT FROM AUTHOR]

Coatings enriched with zinc and copper as well as calcium or magnesium, fabricated on titanium substrate by Plasma Electrolytic Oxidation (PEO) under AC conditions (two cathodic voltages, i.e., −35 or −135 V, and anodic voltage of +400 V), were investigated. In all experiments, the electrolytes were based on concentrated orthophosphoric acid (85 wt%) and zinc, copper, calcium and/or magnesium nitrates. It was found that the introduced calcium and magnesium were in the ranges 5.0–5.4 at% and 5.6–6.5 at%, respectively, while the zinc and copper amounts were in the range of 0.3–0.6 at%. Additionally, it was noted that the metals of the block S (Ca and Mg) could be incorporated into the structure about 13 times more than metals of the transition group (Zn and Cu). The incorporated metals (from the electrolyte) into the top-layer of PEO phosphate coatings were on their first (Cu+) or second (Cu2+, Ca2+ and Mg2+) oxidation states. The crystalline phases (TiO and Ti3O) were detected only in coatings fabricated at cathodic voltage of −135 V. It has also been pointed that fabricated porous calcium–phosphate coatings enriched with biocompatible magnesium as well as with antibacterial zinc and copper are dedicated mainly to medical applications. However, their use for other applications (e.g., catalysis and photocatalysis) after additional functionalizations is not excluded. [ABSTRACT FROM AUTHOR]

This paper shows that the subject of porous coatings fabrication by Plasma Electrolytic Oxidation (PEO), known also as Micro Arc Oxidation (MAO), is still current, inter alia because metals and alloys, which can be treated by the PEO method, for example, titanium, niobium, tantalum and their alloys, are increasingly available for sale. On the international market, apart from scientific works/activity developed at universities, scientific research on the PEO coatings is also underway in companies such as Keronite (Great Britain), Magoxid-Coat (Germany), Mofratech (France), Machaon (Russia), as well as CeraFuse, Tagnite, Microplasmic (USA). In addition, it should be noted that the development of the space industry and implantology will force the production of trouble-free micro- and macro-machines with very high durability. Another aspect in favor of this technique is the rate of part treatment, which does not exceed several dozen minutes, and usually only lasts a few minutes. Another advantage is functionalization of fabricated surface through thermal or hydrothermal modification of fabricated coatings, or other methods (Physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel), including also reoxidation by PEO treatment in another electrolyte. In the following chapters, coatings obtained both in aqueous solutions and electrolytes based on orthophosphoric acid will be presented; therein, dependent on the PEO treatment and the electrolyte used, they are characterized by different properties associated with their subsequent use. The possibilities for using coatings produced by means of plasma electrolytic oxidation are very wide, beginning from various types of catalysts, gas sensors, to biocompatible and antibacterial coatings, as well as hard wear coatings used in machine parts, among others, used in the aviation and aerospace industries. [ABSTRACT FROM AUTHOR]

The present paper covers the possible ways to fabricate advanced porous coatings that are enriched in copper on a titanium substrate through Direct Current Plasma Electrolytic Oxidation (DC-PEO) with voltage control, in electrolytes made of concentrated orthophosphoric acid with the addition of copper(II) nitrate(V) trihydrate. In these studies, solutions containing from 0 to 650 g salt per 1 dm3 of acid and anodic voltages from 450 V up to 650 V were used. The obtained coatings featuring variable porosity could be best defined by the three-dimensional (3D) parameter Sz, which lies in the range 9.72 to 45.18 μm. The use of copper(II) nitrate(V) trihydrate in the electrolyte, resulted, for all cases, in the incorporation of the two oxidation forms, i.e., Cu+ and Cu2+ into the coatings. Detailed X-Ray Photoelectron Spectroscopy (XPS) studies layers allowed for stating that the percentage of copper in the surface layer of the obtained coatings was in the range of 0.24 at% to 2.59 at%. The X-Ray Diffraction (XRD) studies showed the presence of copper (α-Cu2P2O7, and Cu3(PO4)2) and titanium (TiO2-anatase, TiO3, TiP2O7, and Ti0.73O0.91) compounds in coatings. From Energy-Dispersive X-Ray Spectroscopy (EDS) and XPS studies, it was found that the Cu/P ratio increases with the increase of voltage and the amount of salt in the electrolyte. The depth profile analysis by Glow-Discharge Optical Emission Spectroscopy (GDOES) method showed that a three-layer model consisting of a top porous layer, a semi-porous layer, and a transient/barrier layer might describe the fabricated coatings. [ABSTRACT FROM AUTHOR]

To fabricate porous copper coatings on titanium, we used the process of plasma electrolytic oxidation (PEO) with voltage control. For all experiments, the three-phase step-up transformer with six-diode Graetz bridge was used. The voltage and the amount of salt used in the electrolyte were determined so as to obtain porous coatings. Within the framework of this study, the PEO process was carried out at a voltage of 450 VRMS in four electrolytes containing the salt as copper(II) nitrate(V) trihydrate. Moreover, we showed that the content of salt in the electrolyte needed to obtain a porous PEO coating was in the range 300–600 g/dm3. After exceeding this amount of salts in the electrolyte, some inclusions on the sample surface were observed. It is worth noting that this limitation of the amount of salts in the electrolyte was not connected with the maximum solubility of copper(II) nitrate(V) trihydrate in the concentrated (85%) orthophosphoric acid. To characterize the obtained coatings, numerous techniques were used. In this work, we used scanning electron microscopy (SEM) coupled with electron-dispersive X-ray spectroscopy (EDS), conducted surface analysis using confocal laser scanning microscopy (CLSM), and studied the surface layer chemical composition of the obtained coatings by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), glow discharge of optical emission spectroscopy (GDOES), and biological tests. It was found that the higher the concentration of Cu(NO3)2∙3H2O in the electrolyte, the higher the roughness of the coatings, which may be described by 3D roughness parameters, such as Sa (1.17–1.90 μm) and Sp (7.62–13.91 μm). The thicknesses of PEO coatings obtained in the electrolyte with 300–600 g/dm3 Cu(NO3) 2∙3H2O were in the range 7.8 to 10 μm. The Cu/P ratio of the whole volume of coating measured by EDS was in the range 0.05–0.12, while the range for the top layer (measured using XPS) was 0.17–0.24. The atomic concentration of copper (0.54–0.72 at%) resulted in antibacterial and fungicidal properties in the fabricated coatings, which can be dedicated to biocompatible applications. [ABSTRACT FROM AUTHOR]

The bioactive and anti-bacterial Cu-based bioceramic TiO2 coatings have been fabricated on cp-Ti (Grade 2) by two-steps. These two-steps combine micro-arc oxidation (MAO) and physical vapor deposition–thermal evaporation (PVD-TE) techniques for dental implant applications. As a first step, all surfaces of cp-Ti substrate were coated by MAO technique in an alkaline electrolyte, consisting of Na3PO4 and KOH in de-ionized water. Then, as a second step, a copper (Cu) nano-layer with 5 nm thickness was deposited on the MAO by PVD-TE technique. Phase structure, morphology, elemental amounts, thickness, roughness and wettability of the MAO and Cu-based MAO coating surfaces were characterized by XRD (powder- and TF-XRD), SEM, EDS, eddy current device, surface profilometer and contact angle goniometer, respectively. The powder- and TF-XRD spectral analyses showed that Ti, TiO2, anatase-TiO2 and rutile-TiO2 existed on the MAO and Cu-based MAO coatings' surfaces. All coatings' surfaces were porous and rough, owing to the presence of micro sparks through MAO. Furthermore, the surface morphology of Cu-based MAO was not changed. Also, the Cu-based MAO coating has more hydrophilic properties than the MAO coating. In vitro bioactivity and in vitro antibacterial properties of the coatings have been investigated by immersion in simulated body fluid (SBF) at 36.5 °C for 28 days and bacterial adhesion for gram-positive (S. aureus) and gram-negative (E. coli) bacteria, respectively. The apatite layer was formed on the MAO and Cu-based MAO surfaces at post-immersion in SBF and therefore, the bioactivity of Cu-based MAO surface was increased to the MAO surface. Also, for S. aureus and E. coli, the antibacterial properties of Cu-based MAO coatings were significantly improved compared to one of the uncoated MAO surfaces. These results suggested that Cu-based MAO coatings on cp-Ti could be a promising candidate for biomedical dental implant applications. [ABSTRACT FROM AUTHOR]

In the paper, the effect of voltage increase (from 500 VDC up to 650 VDC) on the structure and chemical composition of the porous coating on titanium made by Plasma Electrolytic Oxidation is presented. Phosphates-based coatings enriched with calcium, magnesium, zinc, and copper in electrolyte based on 1 L of 85% concentrated H3PO4, with additions of Ca(NO3)2·4H2O, and Mg(NO3)2∙6H2O, and Zn(NO3)2∙6H2O, and Cu(NO3)2∙3H2O, are described. The morphology and chemical and phase composition are evaluated using SEM, EDS, XRD, XPS, GDOES, and CLSM. Based on these analyses, it was found that PEO coatings are porous and enriched with calcium, magnesium, zinc and copper. They consist mainly of the amorphous phase, which is more visible for higher voltages; this is correlated with an increase in the total PEO coating thickness (the higher the voltage, the thicker the PEO coating). However, for 650 VDC, an amorphous phase and titanium substrate were also recorded, with a signal from Ti2P2O7 crystalline that was not observed for lower voltages. It was also found that all obtained coatings may be divided into three sub-layers, i.e., porous, semiporous, and transitional. [ABSTRACT FROM AUTHOR]