Magnesium alloys are lightweight materials with great potential,and plasma electrolytic oxidation(PEO)is effective surface treatment for necessary improvement of corrosion resistance of magnesium alloys.However,the∼1...Magnesium alloys are lightweight materials with great potential,and plasma electrolytic oxidation(PEO)is effective surface treatment for necessary improvement of corrosion resistance of magnesium alloys.However,the∼14µm thick and rough PEO protection layer has inferior wear resistance,which limits magnesium alloys as sliding or reciprocating parts,where magnesium alloys have special advantages by their inherent damping and denoising properties and attractive light-weighting.Here a novel super wear-resistant coating for magnesium alloys was achieved,via the discontinuous sealing(DCS)of a 1.3µm thick polytetrafluoroethylene(PTFE)polymer layer with an initial area fraction(A_(f))of 70%on the necessary PEO protection layer by selective spraying,and the wear resistance was exceptionally enhanced by∼5500 times in comparison with the base PEO coating.The initial surface roughness(Sa)under PEO+DCS(1.54µm)was imperfectly 59%higher than that under PEO and conventional continuous sealing(CS).Interestingly,DCS was surprisingly 20 times superior for enhancing wear resistance in contrast to CS.DCS induced nano-cracks that splitted DCS layer into multilayer nano-blocks,and DCS also provided extra space for the movement of nano-blocks,which resulted in rolling friction and nano lubrication.Further,DCS promoted mixed wear of the PTFE polymer layer and the PEO coating,and the PTFE layer(HV:6 Kg·mm^(−2),A_(f):92.2%)and the PEO coating(HV:310 Kg·mm^(−2),A_(f):7.8%)served as the soft matrix and the hard point,respectively.Moreover,the dynamic decrease of Sa by 29%during wear also contributed to the super wear resistance.The strategy of depositing a low-frictional discontinuous layer on a rough and hard layer or matrix also opens a window for achieving super wear-resistant coatings in other materials.展开更多
Here we prepared PEO coatings on Mg alloys in silicate-NaOH-phosphate electrolyte containing different concentrations of NaF addition.The detailed microstructural characterizations combining with potentiodynamic polar...Here we prepared PEO coatings on Mg alloys in silicate-NaOH-phosphate electrolyte containing different concentrations of NaF addition.The detailed microstructural characterizations combining with potentiodynamic polarization and electrochemical impedance spectra(EIS)were employed to investigate the roles of fluoride in the growth and corrosion properties of PEO coating on Mg.The result shows the introduction of NaF led to a fluoride-containing nanolayer(FNL)formed at the Mg/coating interface.The FNL consists of MgO nanoparticles and insoluble MgF_(2)nanoparticles(containing rutile phase and cubic phase).The increase in the NaF concentration of the electrolyte increases the thickness and the MgF_(2)content in the FNL.When anodized in the electrolyte containing 2 g/L NaF,the formed FNL has the highest thickness of 100-200 nm along with the highest value of x of∼0.6 in(MgO)_(1-x)(MgF_(2))x resulted in the highest corrosion performance of PEO coating.In addition,when anodized in the electrolyte containing a low NaF concentration(0.4-0.8 g/L),the formed FNL was thin and discontinuous,which would decrease the pore density and increase the coating's uniformness simultaneously.展开更多
Magnesium(Mg) alloys are well-known in biomedical materials owing to their elastic module near to bone, biocompatibility and biodegradation properties. Nevertheless, poor corrosion resistance hinders their biomedical ...Magnesium(Mg) alloys are well-known in biomedical materials owing to their elastic module near to bone, biocompatibility and biodegradation properties. Nevertheless, poor corrosion resistance hinders their biomedical applications. Besides, it is necessary to endow Mg alloys with bioactive property, which is crucial for temporary bone implants. Here, a self-healing, corrosion resistant and bioactive duplex coating of plasma electrolytic oxidization(PEO)/polydopamine(PDA) is applied on AZ91 substrate using PEO and subsequent electrodeposition process. Moreover, the role of different electrodeposition times(60 s, 120 s) and dopamine concentrations(1 and 1.5 mg/ml) to improve corrosion resistance, bioactivity, biocompatibility and self-healing property and its mechanism are investigated. The results indicate that the PEO coating is efficiently sealed by the PDA, depending on the electrodeposition parameters. Noticeably, electrodeposition for 120 s in dopamine concentration of 1 mg/ml(120T-1C) results in the formation of uniform and crack-free PDA coating. Duplex PEO/PDA coatings reveal high bioactivity compared to PEO coating, owing to electrostatic interaction between PDA top-layer and calcium and phosphate ions as well as high hydrophilicity of coatings. In addition, duplex PEO/PDA coatings also show improved and more stable protective performance than the PEO and bare alloy, depending on the PDA deposition parameters. Noticeably, the corrosion current density of the 120T-1C decreases one orders of magnitude compared to PEO. In addition, the presence of a broad passivation region in the anodic polarization branch shows durable self-healing property via Zipper-like mechanism, demonstrating the duplex coating could preserve promising corrosion resistance.Furthermore, the cytocompatibility of duplex coated samples is also confirmed via interaction with MG63 cells. In summary, the PEO/PDA coating with great corrosion protection, self-healing ability, bioactivity and biocompatibility could be a promising candidate for degradable magnesium-based implants.展开更多
In-situ incorporation of layered double hydroxides(LDH)nanocontainers into plasma electrolytic oxidation(PEO)coatings on AZ91 Mg alloy has been achieved in the present study.Fumarate was selected as Mg corrosion inhib...In-situ incorporation of layered double hydroxides(LDH)nanocontainers into plasma electrolytic oxidation(PEO)coatings on AZ91 Mg alloy has been achieved in the present study.Fumarate was selected as Mg corrosion inhibitor for exchange and intercalation into the nanocontainers,which were subsequently incorporated into the coating.It was found that the thickness and compactness of the coatings were increased in the presence of LDH nanocontainers.The corrosion protection performance of the blank PEO,LDH containing PEO and inhibitor loaded coatings was evaluated by means of polarization test and electrochemical impedance spectroscopy(EIS).The degradation process and corrosion resistance of PEO coating were found to be greatly affected by the loaded inhibitor and nanocontainers by means of ion-exchange when corrosion occurs,leading to enhanced and stable corrosion resistance of the substrate.展开更多
Mg and its alloys have been introduced as promising biodegradable materials for biomedical implant applications due to their excellent biocompatibility, mechanical behavior, and biodegradability. However, their suscep...Mg and its alloys have been introduced as promising biodegradable materials for biomedical implant applications due to their excellent biocompatibility, mechanical behavior, and biodegradability. However, their susceptibility to rapid corrosion within the body poses a significant challenge and restricts their applications. To overcome this issue, various surface modification techniques have been developed to enhance the corrosion resistance and bioactivity of Mg-based implants. PEO is a potent technique for producing an oxide film on a surface that significantly minimizes the tendency to corrode. However, the inevitable defects due to discharges and poor biological activity during the coating process remain a concern. Therefore, adding suitable particles during the coating process is a suitable solution. Hydroxyapatite(HAp)has attracted much attention in the development of biomedical applications in the scientific community. HAp shows excellent biocompatibility due to its similarity in chemical composition to the mineral portion of bone. Therefore, its combination with Mg-based implants through PEO has shown significant improvements in their corrosion resistance and bioactivity. This review paper provides a comprehensive overview of the recent advances in the preparation, characterization, corrosion behavior and bioactivity applications of HAp particles on Mg-based implants by PEO.展开更多
This work looked into the influence of the sealing treatment on the structural feature and electrochemical response of AZ31 Mg alloy coated via plasma electrolytic oxidation(PEO).Here,the inorganic layers produced by ...This work looked into the influence of the sealing treatment on the structural feature and electrochemical response of AZ31 Mg alloy coated via plasma electrolytic oxidation(PEO).Here,the inorganic layers produced by PEO in an alkaline-phosphate electrolyte were subsequently immersed for different periods in cold(60°C)and hot(100°C)aqueous solutions containing either 1 or 3 gr of cobalt nitrate hexahydrate in the presence of hydrogen peroxide as an initiator.The results showed that the sealing treatments in the hot solutions could trigger the hydration reactions of PEO coating which would largely assist the surface incorporation of Co_(3)O_(4)into the coating.In contrast,the sealing in cold solutions led to less compact coatings,which was attributed to the fact the hydration reactions would be restricted at 60°C.A nearly fully sealed coating with a porosity of~0.5%was successfully formed on the sample immersed in the hot solution containing 1 gr of cobalt nitrate hexahydrate.Thus,the electrochemical stability of this fully sealed coating was superior to the other samples as it had the lowest corrosion current density(4.71×10^(-10)A·cm^(-2))and the highest outer layer resistance(3.81×10^(7)Ω·cm^(2)).The composite coatings developed in this study are ideal for applications requiring high electrochemical stability.展开更多
Plasma Electrolyte Oxidation(PEO)process has increasingly been employed to improve magnesium surface properties by fabrication of an MgO-based coating.Originating from conventional anodizing procedures,this high-volta...Plasma Electrolyte Oxidation(PEO)process has increasingly been employed to improve magnesium surface properties by fabrication of an MgO-based coating.Originating from conventional anodizing procedures,this high-voltage process produces an adhesive ceramic film on the surface.The present article provides a comprehensive review around mechanisms of PEO coatings fabrication and their different properties.Due to complexity of PEO coatings formation,a complete explanation regarding fabrication mechanisms of PEO coatings has not yet been proposed;however,the most important advancements in the field of fabrication mechanisms of PEO coatings were gathered in this work.Mechanisms of PEO coatings fabrication on magnesium were reviewed considering voltage–time plots,optical spectrometry,acoustic emission spectrometry and electronic properties of the ceramic film.Afterwards,the coatings properties,affecting parameters and improvement strategies were discussed.In addition,corrosion resistance of coatings,important factors in corrosion resistance and methods for corrosion resistance improvement were considered.Tribological properties(important factors and improvement methods)of coatings were also studied.Since magnesium and its alloys are broadly used in biological applications,the biological properties of PEO coatings,important factors in their biological performance and existing methods for improvement of coatings were explained.Addition of ceramic based nanoparticles and formation of nanocomposite coatings may considerably influence properties of plasma electrolyte oxidation coatings.Nanocomposite coatings properties and nanoparticles adsorption mechanisms were included in a separate sector.Another method to improve coatings properties is formation of hybrid coatings on PEO coatings which was discussed in the end.展开更多
Plasma electrolytic oxidation(PEO),a promising surface treatment method to improve the corrosion and wear resistance of magnesium and its alloys,operates at high voltages,resulting in a relatively high energy cost.To ...Plasma electrolytic oxidation(PEO),a promising surface treatment method to improve the corrosion and wear resistance of magnesium and its alloys,operates at high voltages,resulting in a relatively high energy cost.To make the PEO process more economically viable,its energy efficiency needs to be improved.This study investigates the growth behaviour and microstructural characteristics of low-energy PEO coatings on an AM50 magnesium alloy in a concentrated electrolyte containing sodium tetraborate.The surface morphology of the coatings was different from typical PEO coating morphologies and a large voltage oscillation was observed during treatment.Using different characterisation techniques,and based on a micro-discharge model,a correlation was made between the voltage-time behaviour,microdischarge characteristics and the composition and microstructure of the coated samples.The results suggest electrolyte chemistry can somewhat control discharge behaviour,which plays an important role in PEO coating growth.展开更多
The plasma electrolytic oxidation(PEO)procedure is utilized in order to amend the surface properties of Mg and its alloys.This procedure creates a ceramic coating on the surface applying high-voltage.The presence of d...The plasma electrolytic oxidation(PEO)procedure is utilized in order to amend the surface properties of Mg and its alloys.This procedure creates a ceramic coating on the surface applying high-voltage.The presence of deep pores and porosities in the surface that affect the corrosion resistance of the coatings is one of the PEO procedure limitations.One of the useful methods to decrease porosities of coating and improve its final properties is changing electrolyte conditions based on the presence of micro-and nanoparticles.The present paper reviews the mechanisms of particle adsorption and composition in PEO thin films in addition to the effect of particle addition on the microstructure,composition and corrosion behavior of coatings that were applied on magnesium alloys.展开更多
The growth kinetics of PEO coatings on AZ31 and AZ91 magnesium alloys were studied and correlated with their structure,compositions(phase and elemental)and corrosion resistance.It was established that the coatings hav...The growth kinetics of PEO coatings on AZ31 and AZ91 magnesium alloys were studied and correlated with their structure,compositions(phase and elemental)and corrosion resistance.It was established that the coatings have a two-(outer and anodic)or three-layer structure(outer,inner and anodic)depending on the treatment time.Briefly,at short treatment time only an anodic layer and outer layer exists.Growth of the outer PEO layer takes place due to the micro discharges,which occur in vertical pores and voids with spherical cross-section.If the time is increasing,and electrolyte inside of the pores is heating-up,etching of the Mg substrate and oxide film becomes more dominant and horizontal pores in the interface between coating and metal are formed.In the pores new anodic layer will form and at this time the formation of the third inner layer starts.The growth of the inner layer happens via the anodic film as a result of micro discharge ignition in the horizontal pores,accompanied by formation of plasma in numerous micro-voids of this layer.The coatings formed on AZ91 alloy are denser,than those on AZ31,which is related to the difference in the rates of inner layer growth and dissolving of oxides which are located at the bottom of the horizontal pores.Because of the lower Al content,the AZ31 substrate itself and the also the oxide films are less stable and tend to dissolve at a higher rate compared to AZ91.Thus,it was demonstrated that a good corrosion resistance of the coatings was only obtained on AZ91 and if the average thickness of the coating is around 50μm,correlating with the formation of a sufficiently dense inner laye-Knowing this mechanism,a new two-step treatment was suggested,combining the standard PEO treatment with a subsequent PEO process in an electrolyte supporting the inner film formation.The concept was successfully applied and a further improved corrosion resistance was obtained compared to the single stage PEO process.This improvement of corrosion resistance was related to the better sealing of porosity and formation of a denser inner layer.展开更多
Magnesium has been known as an appropriate biological material on account of its good biocompatibility and biodegradability properties in addition to advantageous mechanical properties.Mg and its alloys are of poor co...Magnesium has been known as an appropriate biological material on account of its good biocompatibility and biodegradability properties in addition to advantageous mechanical properties.Mg and its alloys are of poor corrosion resistance.Its high corrosion rate leads to its quick decomposition in the corrosive ambiance and as a result weakening its mechanical properties and before it is repaired,it will vanish.The corrosion and degradation rate must be controlled in the body to advance the usage of Mg and its alloys as implants.Different techniques have been utilized to boost biological properties.Plasma electrolytic oxidation(PEO)can provide porous and biocompatible coatings for implants among various techniques.Biodegradable implants are generally supposed to show enough corrosion resistance and mechanical integrity in the body environment.Much research has been carried out in order to produce PEO coatings containing calcium phosphate compounds.Calcium phosphates are really similar to bone mineral composition and present great biocompatibility.The present study deals with the usage of calcium phosphates as biocompatible coatings applied on Mg and its alloys to study the properties and control the corrosion rate.展开更多
Plasma electrolytic oxidation(PEO)coatings were prepared on AZ91D magnesium alloys in alkaline silicate-based electrolyte with and without additives.The mutual effects among additives including TiC particles,dispersan...Plasma electrolytic oxidation(PEO)coatings were prepared on AZ91D magnesium alloys in alkaline silicate-based electrolyte with and without additives.The mutual effects among additives including TiC particles,dispersant polyethylene glycol 6000(PEG6000)and anionic surfactant sodium dodecyl sulfate(SDS)were studied based on orthogonal experiment.The content and distribution of TiC deposited in the coatings were measured by EPMA and EDS.The thicknesses,phase compositions,microstructures and corrosion resistances of the codlings were cAarnined by using TT260 eddy current tuickncss gage,XRD,SEM and clcctrochcniical test,respectively.The results show that the experiment design of this study is the key to study the mutual effects among these additives.Each additive and their interactions all remarkably influence TiC content and corrosion resistance of the coatings.Smaller size TiC is much easier to migrate towards the anode,and the interaction between PEG6000 and SDS both effectively prevents its agglomeration and increases the number of its negative surface charges,which further increase the migration rate and the deposited uniformity of TiC and make TiC have more opportunity to deposit in the discharge channel.Thus,when smaller size TiC,PEG6000 and SDS are all added into the electrolyte,they could improve the anti-corrosion property of the coating to the largest extent attributed to higher TiC content and the densest microstructure of the coating.展开更多
Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,struct...Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,structure,and phase composition of the coating were investigated by scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion resistance of the coating was evaluated by electrochemical experiment,hydrogen evolution,and immersion test.The results showed that the addition of carbonate resulted in a denser coating with increased hardness,and the corrosion-resistant Li_(2)CO_(3) phase was formed.Electrochemical experiments showed that compared with the coating without carbonate,the corrosion potential of the carbonate coating positively shifted(24 mV),and the corrosion current density was reduced by approximately an order of magnitude.The coating with carbonate addition possessed a high corrosion resistance and long-term protection capability.展开更多
As an efficient surface modification approach,the plasma electrolytic oxidation(PEO)technique can boost the capability of wear protection in Mg and its alloys by applying a hard and thick ceramic coating.In this proce...As an efficient surface modification approach,the plasma electrolytic oxidation(PEO)technique can boost the capability of wear protection in Mg and its alloys by applying a hard and thick ceramic coating.In this procedure,more efficient protection can be acquired via adding additives(in the form of particle,powder,sheet,etc.)into solutions and producing composite coatings.These additives result in more efficient protection against wear via getting stuck in the cracks and pores of coatings and rising the thickness,hardness,and diminishing the porosity size and content.The efficiency of each additive can be changed owing to its intrinsic properties like melting point,size,participation type(reactive,partly reactive,or inert)and potential of zeta.In this review,the effects of distinct additives in nano-and micro-scale size on wear behavior of PEO coatings on Mg and its alloys is going to be reviewed.展开更多
Magnesium(Mg)and its alloys have become a hot research topic in various industries owing to the specific physical and chemical properties.However,high corrosion rate is considered the key lifetime-limiting.Plasma elec...Magnesium(Mg)and its alloys have become a hot research topic in various industries owing to the specific physical and chemical properties.However,high corrosion rate is considered the key lifetime-limiting.Plasma electrolytic oxidation(PEO)method is a simple strategy to deposit an oxide layer on the surface of light metals such as magnesium alloys,to control corrosion rate and promote some other properties,depending on their performances.Nevertheless,their features including their micropore size,distribution,and interconnectivity,and microcracks have not been improved to an acceptable level to support long-term performances of the magnesium-based substrates.Studies have introduced micro/nano-enabled approaches to enhance various properties of PEO coatings such as corrosion resistance,tribological properties,self-healing ability,bioactivity,biocompatibility,antibacterial properties,or catalytic performances.These strategies consist of incorporating of micro and nanoparticles into the PEO layers to produce multi-functional surfaces or the formation of multi-layered coatings to cover the defects of PEO coatings.In this perspective,the present paper aims to overview various nano/micro-enabled strategies to promote the properties of PEO coatings on magnesium alloys.The main focus is given to the functional changes that occurred in response to the incorporation of various types of nano/micro-structures into the PEO coatings on magnesium alloys.展开更多
Plasma electrolytic oxidation(PEO)has held great potential for the advancement of biodegradable implants,as it helps in developing porous bioceramic coatings on the surface of magnesium alloys.In this research work,Mg...Plasma electrolytic oxidation(PEO)has held great potential for the advancement of biodegradable implants,as it helps in developing porous bioceramic coatings on the surface of magnesium alloys.In this research work,MgO-based bioceramic coatings containing the Si,P,Ca,Na,and F elements have been successfully fabricated on an AZ31 magnesium alloy plate utilizing the PEO method.The characteristic current-voltage behavior of the samples during the process was surveyed in an electrolyte containing Ca(H_(2)PO_(4))_(2),Na_(2)SiO_(3)·9H_(2)O,Na_(3)PO_(4)·12H_(2)O,NaF,and KOH with a pH of 12.5 and electrical conductivity of 20 mS/cm^(-1).The results revealed that applying a voltage of 350-400 V(that is 50-100 V higher than the breakdown limit)could greatly facilitate the synthesis of a PEO ceramic coating with fewer defects and more uniform morphology.The resulting coating was a compositionally graded bioceramic layer with a thickness in the range of 3.5±0.4 to 6.0±0.7µm,comprising the above-mentioned elements as promising bioactive agents.The synthesized ceramic features were investigated in terms of the elemental distribution of components through the thickness,which indicated a gradual rise in the Si and P contents and,conversely,a decline in the F content towards the outer surface.The growth mechanism of the PEO coating has been discussed accordingly.展开更多
ZrO2-Y2O3 ceramic coating was produced by plasma electrolytic oxidation (PEO) on ZAlSil2Cu3Ni2 alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD.: The results show that...ZrO2-Y2O3 ceramic coating was produced by plasma electrolytic oxidation (PEO) on ZAlSil2Cu3Ni2 alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD.: The results show that adding an appropriate amount of yttrium ion can improve the growing rate of ceramic coating at different oxidation stages and decrease arc voltage. The thickness of ZrO2-Y2O3 coating is 16 μn thicker than that of ZrO2 coating and the maximum oxidation rate improves by 0.6 μm/min. In addition, the arc voltage decreases from 227 to 172 V. It can be seen that the rate of oxidation firstly increases to some extent and then decreases with the content of yttrium ion increasing. The growth rate reaches the maximum while the content of yttrium ion is 0.05 g-L-1The maximum thickness is 90 μm.Compared to ZrO2 coating, the micropores of ZrO2-Y2O3 coating are less and the ceramic layer is repeatedly deposited by ZrO2 and Y2O3 ceramic particles. Meanwhile, the binding force between coating and substrate is better and the coating is uniform and compact. The ceramic layer is mainly composed of c-Y0.15Zr0.85O1.93□0.07, m-ZrO2, α-Al2O3, ,γ-Al2O3 and Y2O3. It is indicated that ZrO2 has beert fully stabilized by yttrium ion through the formation of solid solution.展开更多
The influence of incorporating different sizes of Si_(3)N_(4) particles on the microstructure and corrosion properties of a phosphate-based plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was inves...The influence of incorporating different sizes of Si_(3)N_(4) particles on the microstructure and corrosion properties of a phosphate-based plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was investigated. The experiments for this study were performed in alkaline electrolytes containing 1 g/L KOH, 10 g/L Na_(3)PO_(4) with and without three different sized of Si_(3)N_(4) particles. The corrosion properties of PEO coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.5 wt.% NaCl solution. Microstructure observations by SEM showed that the surface morphology and composition of the PEO coating were affected greatly by particle addition. Si_(3)N_(4) particles can still be found without decomposition in the final coating due to their high melting point.展开更多
Plasma electrolytic oxidation(PEO)is a promising surface treatment to generate adherent and thick anti-corrosive coating on light-weight metals(Al,Mg,Ti,etc.)using an eco-friendly alkaline electrolyte.High energy plas...Plasma electrolytic oxidation(PEO)is a promising surface treatment to generate adherent and thick anti-corrosive coating on light-weight metals(Al,Mg,Ti,etc.)using an eco-friendly alkaline electrolyte.High energy plasma,however,inevitably generates porous structures that limit their practical performance.The present study proposes a straight-forward simple method by utilizing sub-zero electrolyte(268 K)to alter the plasma characteristics during formation of the protective coating on AZ31 Mg alloy via PEO with a comparison to the electrolyte at room temperature(298 K).In refrigerated electrolyte,the formation of micro-defects is suppressed relatively at the expense of low coating growth,which is measured to be twice lower than that at 298 K due to the temperature-dependent soft plasma discharges contributing to the development of the present coating.As a consequence,corrosion resistance of the sample processed at 268 K is superior to that of 298K,implying that the effect of coating thickness is less dominant than that of compactness.This phenomenon is interpreted in relation to the ionic movement and oxide solidification controlled by soft plasma discharges arising from the temperature gradient between electrolyte and surface of the substrate during PEO.展开更多
基金This work was financially supported by the Jiangsu Distinguished Professor Project,the Innovate UK(Project reference:10004694)the National Key R&D Program of China 2021YFB3401200.The Experimental Techniques Centre at Brunel University London and Nanjing University of Aeronautics and Astronautics are acknowledged.The authors also acknowledge the characterization facility at Shanghai Jiao Tong University,Central South University,University of Birmingham and University of Lille.
文摘Magnesium alloys are lightweight materials with great potential,and plasma electrolytic oxidation(PEO)is effective surface treatment for necessary improvement of corrosion resistance of magnesium alloys.However,the∼14µm thick and rough PEO protection layer has inferior wear resistance,which limits magnesium alloys as sliding or reciprocating parts,where magnesium alloys have special advantages by their inherent damping and denoising properties and attractive light-weighting.Here a novel super wear-resistant coating for magnesium alloys was achieved,via the discontinuous sealing(DCS)of a 1.3µm thick polytetrafluoroethylene(PTFE)polymer layer with an initial area fraction(A_(f))of 70%on the necessary PEO protection layer by selective spraying,and the wear resistance was exceptionally enhanced by∼5500 times in comparison with the base PEO coating.The initial surface roughness(Sa)under PEO+DCS(1.54µm)was imperfectly 59%higher than that under PEO and conventional continuous sealing(CS).Interestingly,DCS was surprisingly 20 times superior for enhancing wear resistance in contrast to CS.DCS induced nano-cracks that splitted DCS layer into multilayer nano-blocks,and DCS also provided extra space for the movement of nano-blocks,which resulted in rolling friction and nano lubrication.Further,DCS promoted mixed wear of the PTFE polymer layer and the PEO coating,and the PTFE layer(HV:6 Kg·mm^(−2),A_(f):92.2%)and the PEO coating(HV:310 Kg·mm^(−2),A_(f):7.8%)served as the soft matrix and the hard point,respectively.Moreover,the dynamic decrease of Sa by 29%during wear also contributed to the super wear resistance.The strategy of depositing a low-frictional discontinuous layer on a rough and hard layer or matrix also opens a window for achieving super wear-resistant coatings in other materials.
基金Zhu.L.and Li.H.contributed equally to this work.This work is supported by the National Natural Science Foundation of China(Grant No.51901121)the Natural Science Foundation of Shaanxi Province(Grant No.2021JM-203,2019JQ-433,2020zdzx04-03-02)the Fundamental Research Funds for the Central Universities(Grant No.GK202103022).
文摘Here we prepared PEO coatings on Mg alloys in silicate-NaOH-phosphate electrolyte containing different concentrations of NaF addition.The detailed microstructural characterizations combining with potentiodynamic polarization and electrochemical impedance spectra(EIS)were employed to investigate the roles of fluoride in the growth and corrosion properties of PEO coating on Mg.The result shows the introduction of NaF led to a fluoride-containing nanolayer(FNL)formed at the Mg/coating interface.The FNL consists of MgO nanoparticles and insoluble MgF_(2)nanoparticles(containing rutile phase and cubic phase).The increase in the NaF concentration of the electrolyte increases the thickness and the MgF_(2)content in the FNL.When anodized in the electrolyte containing 2 g/L NaF,the formed FNL has the highest thickness of 100-200 nm along with the highest value of x of∼0.6 in(MgO)_(1-x)(MgF_(2))x resulted in the highest corrosion performance of PEO coating.In addition,when anodized in the electrolyte containing a low NaF concentration(0.4-0.8 g/L),the formed FNL was thin and discontinuous,which would decrease the pore density and increase the coating's uniformness simultaneously.
文摘Magnesium(Mg) alloys are well-known in biomedical materials owing to their elastic module near to bone, biocompatibility and biodegradation properties. Nevertheless, poor corrosion resistance hinders their biomedical applications. Besides, it is necessary to endow Mg alloys with bioactive property, which is crucial for temporary bone implants. Here, a self-healing, corrosion resistant and bioactive duplex coating of plasma electrolytic oxidization(PEO)/polydopamine(PDA) is applied on AZ91 substrate using PEO and subsequent electrodeposition process. Moreover, the role of different electrodeposition times(60 s, 120 s) and dopamine concentrations(1 and 1.5 mg/ml) to improve corrosion resistance, bioactivity, biocompatibility and self-healing property and its mechanism are investigated. The results indicate that the PEO coating is efficiently sealed by the PDA, depending on the electrodeposition parameters. Noticeably, electrodeposition for 120 s in dopamine concentration of 1 mg/ml(120T-1C) results in the formation of uniform and crack-free PDA coating. Duplex PEO/PDA coatings reveal high bioactivity compared to PEO coating, owing to electrostatic interaction between PDA top-layer and calcium and phosphate ions as well as high hydrophilicity of coatings. In addition, duplex PEO/PDA coatings also show improved and more stable protective performance than the PEO and bare alloy, depending on the PDA deposition parameters. Noticeably, the corrosion current density of the 120T-1C decreases one orders of magnitude compared to PEO. In addition, the presence of a broad passivation region in the anodic polarization branch shows durable self-healing property via Zipper-like mechanism, demonstrating the duplex coating could preserve promising corrosion resistance.Furthermore, the cytocompatibility of duplex coated samples is also confirmed via interaction with MG63 cells. In summary, the PEO/PDA coating with great corrosion protection, self-healing ability, bioactivity and biocompatibility could be a promising candidate for degradable magnesium-based implants.
基金support from National Natural Science Foundation of China(No.52071067 and U1737102)Mobility Programme of the Sino-German Center(M-0056)+1 种基金the Fundamental Research Funds for the Central Universities(N2002009)FUNCOAT project(H2020-MSCA-RISE-2018,Grant Agreement N 823942).
文摘In-situ incorporation of layered double hydroxides(LDH)nanocontainers into plasma electrolytic oxidation(PEO)coatings on AZ91 Mg alloy has been achieved in the present study.Fumarate was selected as Mg corrosion inhibitor for exchange and intercalation into the nanocontainers,which were subsequently incorporated into the coating.It was found that the thickness and compactness of the coatings were increased in the presence of LDH nanocontainers.The corrosion protection performance of the blank PEO,LDH containing PEO and inhibitor loaded coatings was evaluated by means of polarization test and electrochemical impedance spectroscopy(EIS).The degradation process and corrosion resistance of PEO coating were found to be greatly affected by the loaded inhibitor and nanocontainers by means of ion-exchange when corrosion occurs,leading to enhanced and stable corrosion resistance of the substrate.
文摘Mg and its alloys have been introduced as promising biodegradable materials for biomedical implant applications due to their excellent biocompatibility, mechanical behavior, and biodegradability. However, their susceptibility to rapid corrosion within the body poses a significant challenge and restricts their applications. To overcome this issue, various surface modification techniques have been developed to enhance the corrosion resistance and bioactivity of Mg-based implants. PEO is a potent technique for producing an oxide film on a surface that significantly minimizes the tendency to corrode. However, the inevitable defects due to discharges and poor biological activity during the coating process remain a concern. Therefore, adding suitable particles during the coating process is a suitable solution. Hydroxyapatite(HAp)has attracted much attention in the development of biomedical applications in the scientific community. HAp shows excellent biocompatibility due to its similarity in chemical composition to the mineral portion of bone. Therefore, its combination with Mg-based implants through PEO has shown significant improvements in their corrosion resistance and bioactivity. This review paper provides a comprehensive overview of the recent advances in the preparation, characterization, corrosion behavior and bioactivity applications of HAp particles on Mg-based implants by PEO.
基金supported by the National Research Foundation of Korea(NRF)funded by the Korean government(MSIT)(No.2022R1A2C1006743)
文摘This work looked into the influence of the sealing treatment on the structural feature and electrochemical response of AZ31 Mg alloy coated via plasma electrolytic oxidation(PEO).Here,the inorganic layers produced by PEO in an alkaline-phosphate electrolyte were subsequently immersed for different periods in cold(60°C)and hot(100°C)aqueous solutions containing either 1 or 3 gr of cobalt nitrate hexahydrate in the presence of hydrogen peroxide as an initiator.The results showed that the sealing treatments in the hot solutions could trigger the hydration reactions of PEO coating which would largely assist the surface incorporation of Co_(3)O_(4)into the coating.In contrast,the sealing in cold solutions led to less compact coatings,which was attributed to the fact the hydration reactions would be restricted at 60°C.A nearly fully sealed coating with a porosity of~0.5%was successfully formed on the sample immersed in the hot solution containing 1 gr of cobalt nitrate hexahydrate.Thus,the electrochemical stability of this fully sealed coating was superior to the other samples as it had the lowest corrosion current density(4.71×10^(-10)A·cm^(-2))and the highest outer layer resistance(3.81×10^(7)Ω·cm^(2)).The composite coatings developed in this study are ideal for applications requiring high electrochemical stability.
文摘Plasma Electrolyte Oxidation(PEO)process has increasingly been employed to improve magnesium surface properties by fabrication of an MgO-based coating.Originating from conventional anodizing procedures,this high-voltage process produces an adhesive ceramic film on the surface.The present article provides a comprehensive review around mechanisms of PEO coatings fabrication and their different properties.Due to complexity of PEO coatings formation,a complete explanation regarding fabrication mechanisms of PEO coatings has not yet been proposed;however,the most important advancements in the field of fabrication mechanisms of PEO coatings were gathered in this work.Mechanisms of PEO coatings fabrication on magnesium were reviewed considering voltage–time plots,optical spectrometry,acoustic emission spectrometry and electronic properties of the ceramic film.Afterwards,the coatings properties,affecting parameters and improvement strategies were discussed.In addition,corrosion resistance of coatings,important factors in corrosion resistance and methods for corrosion resistance improvement were considered.Tribological properties(important factors and improvement methods)of coatings were also studied.Since magnesium and its alloys are broadly used in biological applications,the biological properties of PEO coatings,important factors in their biological performance and existing methods for improvement of coatings were explained.Addition of ceramic based nanoparticles and formation of nanocomposite coatings may considerably influence properties of plasma electrolyte oxidation coatings.Nanocomposite coatings properties and nanoparticles adsorption mechanisms were included in a separate sector.Another method to improve coatings properties is formation of hybrid coatings on PEO coatings which was discussed in the end.
基金supported by Natural Science and En-gineering Research Council of Canada(NSERC)grant.
文摘Plasma electrolytic oxidation(PEO),a promising surface treatment method to improve the corrosion and wear resistance of magnesium and its alloys,operates at high voltages,resulting in a relatively high energy cost.To make the PEO process more economically viable,its energy efficiency needs to be improved.This study investigates the growth behaviour and microstructural characteristics of low-energy PEO coatings on an AM50 magnesium alloy in a concentrated electrolyte containing sodium tetraborate.The surface morphology of the coatings was different from typical PEO coating morphologies and a large voltage oscillation was observed during treatment.Using different characterisation techniques,and based on a micro-discharge model,a correlation was made between the voltage-time behaviour,microdischarge characteristics and the composition and microstructure of the coated samples.The results suggest electrolyte chemistry can somewhat control discharge behaviour,which plays an important role in PEO coating growth.
文摘The plasma electrolytic oxidation(PEO)procedure is utilized in order to amend the surface properties of Mg and its alloys.This procedure creates a ceramic coating on the surface applying high-voltage.The presence of deep pores and porosities in the surface that affect the corrosion resistance of the coatings is one of the PEO procedure limitations.One of the useful methods to decrease porosities of coating and improve its final properties is changing electrolyte conditions based on the presence of micro-and nanoparticles.The present paper reviews the mechanisms of particle adsorption and composition in PEO thin films in addition to the effect of particle addition on the microstructure,composition and corrosion behavior of coatings that were applied on magnesium alloys.
基金The authors would like to thank ACTICOAT project in frame of Era.NET-Rus+Call,2017(Project N477)RFBR(Project No.18-53-76008)in the frame of project ACTICOAT(Era.Net RUS Plus Call 2017,Project 477)for the partial financial support of this work.MS,MZ and CB additionally appreciate European project FUNCOAT("Development and design of novel multiFUNctional PEO COATings"in frame of H2020-MSCA-RISE-2018 call,Grant Agreement No 823942)for the financial assistance.
文摘The growth kinetics of PEO coatings on AZ31 and AZ91 magnesium alloys were studied and correlated with their structure,compositions(phase and elemental)and corrosion resistance.It was established that the coatings have a two-(outer and anodic)or three-layer structure(outer,inner and anodic)depending on the treatment time.Briefly,at short treatment time only an anodic layer and outer layer exists.Growth of the outer PEO layer takes place due to the micro discharges,which occur in vertical pores and voids with spherical cross-section.If the time is increasing,and electrolyte inside of the pores is heating-up,etching of the Mg substrate and oxide film becomes more dominant and horizontal pores in the interface between coating and metal are formed.In the pores new anodic layer will form and at this time the formation of the third inner layer starts.The growth of the inner layer happens via the anodic film as a result of micro discharge ignition in the horizontal pores,accompanied by formation of plasma in numerous micro-voids of this layer.The coatings formed on AZ91 alloy are denser,than those on AZ31,which is related to the difference in the rates of inner layer growth and dissolving of oxides which are located at the bottom of the horizontal pores.Because of the lower Al content,the AZ31 substrate itself and the also the oxide films are less stable and tend to dissolve at a higher rate compared to AZ91.Thus,it was demonstrated that a good corrosion resistance of the coatings was only obtained on AZ91 and if the average thickness of the coating is around 50μm,correlating with the formation of a sufficiently dense inner laye-Knowing this mechanism,a new two-step treatment was suggested,combining the standard PEO treatment with a subsequent PEO process in an electrolyte supporting the inner film formation.The concept was successfully applied and a further improved corrosion resistance was obtained compared to the single stage PEO process.This improvement of corrosion resistance was related to the better sealing of porosity and formation of a denser inner layer.
文摘Magnesium has been known as an appropriate biological material on account of its good biocompatibility and biodegradability properties in addition to advantageous mechanical properties.Mg and its alloys are of poor corrosion resistance.Its high corrosion rate leads to its quick decomposition in the corrosive ambiance and as a result weakening its mechanical properties and before it is repaired,it will vanish.The corrosion and degradation rate must be controlled in the body to advance the usage of Mg and its alloys as implants.Different techniques have been utilized to boost biological properties.Plasma electrolytic oxidation(PEO)can provide porous and biocompatible coatings for implants among various techniques.Biodegradable implants are generally supposed to show enough corrosion resistance and mechanical integrity in the body environment.Much research has been carried out in order to produce PEO coatings containing calcium phosphate compounds.Calcium phosphates are really similar to bone mineral composition and present great biocompatibility.The present study deals with the usage of calcium phosphates as biocompatible coatings applied on Mg and its alloys to study the properties and control the corrosion rate.
基金The authors are grateful to the Department of Science&Technology of Gansu Province(China)for the support of the Creative Research Group Fund Grant(1111RJDA011)the Open Fund(SKLAB02015006)from State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals(China).
文摘Plasma electrolytic oxidation(PEO)coatings were prepared on AZ91D magnesium alloys in alkaline silicate-based electrolyte with and without additives.The mutual effects among additives including TiC particles,dispersant polyethylene glycol 6000(PEG6000)and anionic surfactant sodium dodecyl sulfate(SDS)were studied based on orthogonal experiment.The content and distribution of TiC deposited in the coatings were measured by EPMA and EDS.The thicknesses,phase compositions,microstructures and corrosion resistances of the codlings were cAarnined by using TT260 eddy current tuickncss gage,XRD,SEM and clcctrochcniical test,respectively.The results show that the experiment design of this study is the key to study the mutual effects among these additives.Each additive and their interactions all remarkably influence TiC content and corrosion resistance of the coatings.Smaller size TiC is much easier to migrate towards the anode,and the interaction between PEG6000 and SDS both effectively prevents its agglomeration and increases the number of its negative surface charges,which further increase the migration rate and the deposited uniformity of TiC and make TiC have more opportunity to deposit in the discharge channel.Thus,when smaller size TiC,PEG6000 and SDS are all added into the electrolyte,they could improve the anti-corrosion property of the coating to the largest extent attributed to higher TiC content and the densest microstructure of the coating.
基金the Natural Science Foundation of China (Nos.51771060,51871068,51971071,and 52011530025)the Domain Foundation of Equipment Advance Research of 13th Five-year Plan,China(No.61409220118)+1 种基金the Zhejiang Province Key Research and Development Program,China (No.2021C01086)the Open Foundation of Key Laboratory of Superlight Materials&Surface Technology of Ministry of Education,China (No.HEU10202104)
文摘Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,structure,and phase composition of the coating were investigated by scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion resistance of the coating was evaluated by electrochemical experiment,hydrogen evolution,and immersion test.The results showed that the addition of carbonate resulted in a denser coating with increased hardness,and the corrosion-resistant Li_(2)CO_(3) phase was formed.Electrochemical experiments showed that compared with the coating without carbonate,the corrosion potential of the carbonate coating positively shifted(24 mV),and the corrosion current density was reduced by approximately an order of magnitude.The coating with carbonate addition possessed a high corrosion resistance and long-term protection capability.
文摘As an efficient surface modification approach,the plasma electrolytic oxidation(PEO)technique can boost the capability of wear protection in Mg and its alloys by applying a hard and thick ceramic coating.In this procedure,more efficient protection can be acquired via adding additives(in the form of particle,powder,sheet,etc.)into solutions and producing composite coatings.These additives result in more efficient protection against wear via getting stuck in the cracks and pores of coatings and rising the thickness,hardness,and diminishing the porosity size and content.The efficiency of each additive can be changed owing to its intrinsic properties like melting point,size,participation type(reactive,partly reactive,or inert)and potential of zeta.In this review,the effects of distinct additives in nano-and micro-scale size on wear behavior of PEO coatings on Mg and its alloys is going to be reviewed.
文摘Magnesium(Mg)and its alloys have become a hot research topic in various industries owing to the specific physical and chemical properties.However,high corrosion rate is considered the key lifetime-limiting.Plasma electrolytic oxidation(PEO)method is a simple strategy to deposit an oxide layer on the surface of light metals such as magnesium alloys,to control corrosion rate and promote some other properties,depending on their performances.Nevertheless,their features including their micropore size,distribution,and interconnectivity,and microcracks have not been improved to an acceptable level to support long-term performances of the magnesium-based substrates.Studies have introduced micro/nano-enabled approaches to enhance various properties of PEO coatings such as corrosion resistance,tribological properties,self-healing ability,bioactivity,biocompatibility,antibacterial properties,or catalytic performances.These strategies consist of incorporating of micro and nanoparticles into the PEO layers to produce multi-functional surfaces or the formation of multi-layered coatings to cover the defects of PEO coatings.In this perspective,the present paper aims to overview various nano/micro-enabled strategies to promote the properties of PEO coatings on magnesium alloys.The main focus is given to the functional changes that occurred in response to the incorporation of various types of nano/micro-structures into the PEO coatings on magnesium alloys.
文摘Plasma electrolytic oxidation(PEO)has held great potential for the advancement of biodegradable implants,as it helps in developing porous bioceramic coatings on the surface of magnesium alloys.In this research work,MgO-based bioceramic coatings containing the Si,P,Ca,Na,and F elements have been successfully fabricated on an AZ31 magnesium alloy plate utilizing the PEO method.The characteristic current-voltage behavior of the samples during the process was surveyed in an electrolyte containing Ca(H_(2)PO_(4))_(2),Na_(2)SiO_(3)·9H_(2)O,Na_(3)PO_(4)·12H_(2)O,NaF,and KOH with a pH of 12.5 and electrical conductivity of 20 mS/cm^(-1).The results revealed that applying a voltage of 350-400 V(that is 50-100 V higher than the breakdown limit)could greatly facilitate the synthesis of a PEO ceramic coating with fewer defects and more uniform morphology.The resulting coating was a compositionally graded bioceramic layer with a thickness in the range of 3.5±0.4 to 6.0±0.7µm,comprising the above-mentioned elements as promising bioactive agents.The synthesized ceramic features were investigated in terms of the elemental distribution of components through the thickness,which indicated a gradual rise in the Si and P contents and,conversely,a decline in the F content towards the outer surface.The growth mechanism of the PEO coating has been discussed accordingly.
基金Funded by the National Natural Science Foundation of China(No.51401155)the School Foundation(No.XAGDXJJ1012)The Open Fund of Shaanxi Key Laboratory of Photoelectric Functional Materials and Devices(No.ZSKJ201416)
文摘ZrO2-Y2O3 ceramic coating was produced by plasma electrolytic oxidation (PEO) on ZAlSil2Cu3Ni2 alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD.: The results show that adding an appropriate amount of yttrium ion can improve the growing rate of ceramic coating at different oxidation stages and decrease arc voltage. The thickness of ZrO2-Y2O3 coating is 16 μn thicker than that of ZrO2 coating and the maximum oxidation rate improves by 0.6 μm/min. In addition, the arc voltage decreases from 227 to 172 V. It can be seen that the rate of oxidation firstly increases to some extent and then decreases with the content of yttrium ion increasing. The growth rate reaches the maximum while the content of yttrium ion is 0.05 g-L-1The maximum thickness is 90 μm.Compared to ZrO2 coating, the micropores of ZrO2-Y2O3 coating are less and the ceramic layer is repeatedly deposited by ZrO2 and Y2O3 ceramic particles. Meanwhile, the binding force between coating and substrate is better and the coating is uniform and compact. The ceramic layer is mainly composed of c-Y0.15Zr0.85O1.93□0.07, m-ZrO2, α-Al2O3, ,γ-Al2O3 and Y2O3. It is indicated that ZrO2 has beert fully stabilized by yttrium ion through the formation of solid solution.
文摘The influence of incorporating different sizes of Si_(3)N_(4) particles on the microstructure and corrosion properties of a phosphate-based plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was investigated. The experiments for this study were performed in alkaline electrolytes containing 1 g/L KOH, 10 g/L Na_(3)PO_(4) with and without three different sized of Si_(3)N_(4) particles. The corrosion properties of PEO coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.5 wt.% NaCl solution. Microstructure observations by SEM showed that the surface morphology and composition of the PEO coating were affected greatly by particle addition. Si_(3)N_(4) particles can still be found without decomposition in the final coating due to their high melting point.
基金the Mid-Level Researcher National Project of the National Research Foundation(NRF)funded by the Ministry of Science and ICT,Republic of Korea(NRF-2020R1A2C2004192)supported partly by the Competency Development Program for Industry Specialist of the Korea Institute for Advancement of Technology(KIAT)funded by the Ministry of Trade,Industry,and Energy,Republic of Korea(P0002019)。
文摘Plasma electrolytic oxidation(PEO)is a promising surface treatment to generate adherent and thick anti-corrosive coating on light-weight metals(Al,Mg,Ti,etc.)using an eco-friendly alkaline electrolyte.High energy plasma,however,inevitably generates porous structures that limit their practical performance.The present study proposes a straight-forward simple method by utilizing sub-zero electrolyte(268 K)to alter the plasma characteristics during formation of the protective coating on AZ31 Mg alloy via PEO with a comparison to the electrolyte at room temperature(298 K).In refrigerated electrolyte,the formation of micro-defects is suppressed relatively at the expense of low coating growth,which is measured to be twice lower than that at 298 K due to the temperature-dependent soft plasma discharges contributing to the development of the present coating.As a consequence,corrosion resistance of the sample processed at 268 K is superior to that of 298K,implying that the effect of coating thickness is less dominant than that of compactness.This phenomenon is interpreted in relation to the ionic movement and oxide solidification controlled by soft plasma discharges arising from the temperature gradient between electrolyte and surface of the substrate during PEO.