Enhancing corrosion resistance of plasma electrolytic oxidation coatings on AM50 Mg alloy by inhibitor containing Ba(NO_(3))_(2) solutions

To enhance the long-term corrosion resistance of the plasma electrolytic oxidation(PEO)coating on the magnesium(Mg)alloy,an inorganic salt combined with corrosion inhibitors was used for posttreatment of the coating.In this study,the corrosion performance of PEO-coated AM50 Mg was significantly improved by loading sodium lauryl sulfonate(SDS)and sodium dodecyl benzene sulf-onate into Ba(NO_(3))_(2) post-sealing solutions.Scanning electron microscopy,X-ray photoelectron spectroscopy,X-ray diffraction,Fourier transform infrared spectrometer,and ultraviolet-visible analyses showed that the inhibitors enhanced the incorporation of BaO_(2) into PEO coatings.Electrochemical impedance showed that post-sealing in Ba(NO_(3))_(2)/SDS treatment enhanced corrosion resistance by three orders of magnitude.The total impedance value remained at 926Ω·cm^(2)after immersing in a 0.5wt%NaCl solution for 768 h.A salt spray test for 40 days did not show any obvious region of corrosion,proving excellent post-sealing by Ba(NO_(3))_(2)/SDS treatment.The corrosion resistance of the coating was enhanced through the synergistic effect of BaO2 pore sealing and SDS adsorption.

Diluent decomposition-assisted formation of Li F-rich solid-electrolyte interfaces enables high-energy Li-metal batteries

Passivation by the inorganic-rich solid electrolyte interphase(SEI),especially the LiF-rich SEI,is highly desirable to guarantee the durable lifespan of Li metal batteries(LMBs).Here,we report a diluent with the capability to facilitate the formation of LiF-rich SEI while avoiding the excess consumption of Li salts.Dissimilar to most of reported inert diluents,heptafluoro-l-methoxypropane(HM) is firstly demonstrated to cooperate with the decomposition of anions to generate LiF-rich SEI via releasing Fcontaining species near Li surface.The designed electrolyte consisting of 1.8 M LiFSI in the mixture of1,2-dimethoxyethane(DME)/HM(2:1 by vol.) achieves excellent compatibility with both Li metal anodes(Coulombic efficiency~99.8%) and high-voltage cathodes(4.4 V LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811) and 4.5 V LiCoO_(2)(LCO) vs Li^(+)/Li).The 4.4 V Li(20μm)‖NMC811(2.5 mA h cm^(-2)) and 4.5 V Li(20μm)‖LCO(2.5 mA h cm^(-2)) cells achieve capacity retentions of 80% over 560 cycles and 80% over 505 cycles,respectively.Meanwhile,the anode-free pouch cell delivers an energy density of~293 W h kg^(-1)initially and retains 70% of capacity after 100 deep cycles.This work highlights the critical impact of diluent on the SEI formation,and opens up a new direction for designing desirable interfacial chemistries to enable high-performance LMBs.

Incorporation of LDH nanocontainers into plasma electrolytic oxidation coatings on Mg alloy

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.

Improvement on the Corrosion Resistance of AZ91D Magnesium Alloy by Aluminum Diffusion Coating

By combination of magnetron sputtering deposition and vacuum annealing, an aluminum diffusion coating was prepared on the substrate of AZ91D alloy to improve its corrosion resistance. The microstructure and composition of the diffusion coating was investigated by scanning electron microscopy and X-ray diffraction. The diffusion coating was mainly comprised of β phase-Al12Mg17. The continuous immersion test in 3.5 wt pct neutral NaCl solution indicated that the specimen with diffusion coating had better corrosion resistance compared with the bare AZ91D alloy specimen. The potentiodynamic polarization measurement indicated that the diffusion coating could function as an effectively protective layer to reduce the corrosion rate of AZ91D alloy when exposed to 3.5 wt pct NaCl solution.

Effect of phosphate-based sealing treatment on the corrosion performance of a PEO coated AZ91D mg alloy

This study investigated the effect of sealing treatment on the corrosion performance of plasma electrolytic oxidation(PEO)coated AZ91D Mg alloy with and without addition of corrosion inhibitor.The microstructure,phase composition and corrosion property of the sealed and unsealed coatings were evaluated by using scanning electron microscopy(SEM),energy dispersion spectroscopy(EDS),x-ray diffraction(XRD),x-ray photoelectron spectroscopy(XPS),polarization,and electrochemical impedance spectroscopy(EIS)tests.Electrochemical experiments and salt spray tests showed that,after sealing in phosphate solution containing corrosion inhibitor,the corrosion current density of PEO-coated AZ91D decreased more than 10-fold and the anti-corrosion time in a salt spray environment increased more than three-fold.The corrosion rate of the PEO coating slowed down due to the releasing and adsorbing of the corrosion inhibitors in the pores and cracks of the coating during the corrosion process.

New design principles for the bath towards chromate-and crack-free conversion coatings on magnesium alloys

Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new principles regarding the design of conversion bath were proposed.The treatment bath should be composed of species that can be categorized into two groups:the first group of species that react with Mg substrate to increase the local p H at the interface;the second group that precipitate and contributes to the growth of coating.The species belong to second group exists in a supersaturated state and its precipitation process is almost independent on the reactions of the species in first group.By this way,a thick and crack-free two-layered conversion coating is obtained.Moreover,the nature of the adjustment of TA/p H and the roles of the oxidizing agent and catalyst were discussed.

A self-healing coating based on facile pH-responsive nanocontainers for corrosion protection of magnesium alloy

The preparation of pH-responsive nanocontainers by typical silane modification of the mesoporous silica nanoparticle(MSN)surface is usually high-cost,complex,and time-consuming,which remains a great challenge for effective corrosion protection of magnesium alloy.Here,a new strategy to construct pH-responsive nanocontainers(MSN-MBT@LDH)is demonstrated.The nanocontainers consist of corrosion inhibitor(2-mercaptobenzothiazole,MBT)loaded MSN core and layered double hydroxide(LDH)nanosheet shell serving as gatekeepers.The successful loading of MBT and encapsulation by LDH nanosheets were confirmed by a series of characterization such as scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy(STEM-EDS)and N2 adsorption/desorption isotherms.The pH-responsive feature of the nanocontainers was demonstrated by determination of the MBT concentration in buffer solutions with different pH values.A smart corrosion protection system on Mg alloy is obtained by incorporating the synthesized nanocontainers into a self-assembled nanophase particle(SNAP)coating.The electrochemical tests and visual observations show that the hybrid coating has the best barrier properties and robustness in corrosion protection in NaCl corrosive solutions in comparison with the control coatings.The present method simplifies the synthesis processes of nanocontainers and eliminates the potential detrimental effect of excess gatekeepers on the coating.The findings provide new insights into the preparation of scalable nanocontainers.The self-healing coatings are expected to have widespread applications for corrosion protection of Mg alloy and other metals.

Passivation of corrosion product layer on AM50 Mg by corrosion inhibitor

The influence of sodium dodecyl sulfate(SDS)on morphology and chemical composition of corrosion product layer formed onα-Mg matrix and cathodic Al-Mn intermetallic was systematically investigated by using FIB and TEM analysis for the first time to disclose the underlying inhibition mechanism.A porous corrosion bi-layer composed of crystalline MgO and Mg(OH)_(2)was observed on both ofα-Mg and Al-Mn intermetallic.It was found that a passive inner layer was deposited onα-Mg after immersion in SDS-containing NaCl solution,which can be ascribed to steady-state growth of magnesium and aluminum oxide under the protection of hydrophobic group of SDS.The inhibition mechanism of the inhibitor was mainly associated with formation of dense oxide layer onα-Mg matrix and preferential adsorption of SDS on the corrosion layer deposited on Al-Mn intermetallic.

Influence of Al Content on the Atmospheric Corrosion Behaviour of Magnesium-Aluminum Alloys

The influence of AI content on the Mg-AI alloys corrosion performance during sodium chloride induced atmospheric corrosion has been studied. It was found that the corrosion rate of three Mg-AI alloys was accelerated with increasing AI content. The poor corrosion resistance was attributed to the galvanic coupling between the phase and eutectic phase or α phase and the formation of porous corrosion products.

HOT CORROSION BEHAVIOR OF K38G ALLOY AND ITS SPUTTERED NANOCRYSTALLINE COATING BY PRE-DEPOSITED SULFATE AT 900℃

The sputtered nanocrystalline coating of K38G alloy was obtained by magnetron sput-tering. The hot corrosion behaviors of cast K38G alloy and its sputtered nanocrys-talline coating by pre-deposited 75wt%Na2SO4+25wt%K2SO4 at 900℃ were studied. The results indicated the occurrence of internal sulfidation in the cast K38G alloy with pre-deposited sulfattes of 0.8 and 3.0mg/cm2. However, the internal sulfidation was not observed in the coating with pre-deposited 0.8mg/cm2 sulfate. The hot corrosion resistance of K38G alloy was clearly enhanced through nanocrystallinzation, although the internal sulfides were still formed for the coating with sulfate deposit of 3mg/cm2. The relevant hot corrosion mechanism was also discussed.

Water vapor effects on the oxidation resistance of modified potassium silicate coating at high temperature

An inorganic potassium silicate coating with pigments of alumina,aluminum phosphate,NiCrAlY and copper chromite black was prepared on CB2 stainless steel.Oxidation behavior in either ambient air or O_(2)+H_(2) O mixture at 630℃ for 2000 h was comparatively studied,and the coating exhibited excellent resistance under both test conditions.The water vapor considerably accelerated the oxidation of the uncoated CB2 steel,as the hydroxide,the main constituent of the coating,had a negligible evaporation rate at test temperature,while it had a limited effect on the coated sample.Meanwhile,the existence of coating may prolong or eliminate the incubation period in the O_(2)+H_(2) O mixture at 630℃.After oxidation,the coating matrix is in an amorphous state and fillers as alumina and copper chromite black are stable in the coating.Leucite(KAlSi_(2) O_(6))formed by Al from NiCrAlY and potassium silicate in the coatings was detected after tests either in O_(2) or O_(2)+H_(2) O mixture.

Effect of exogenous flavins on the microbial corrosion by Geobacter sulfurreducens via iron-to-microbe electron transfer

Microbes can cause or accelerate metal corrosion,leading to huge losses in corrosion damages each year.Geobacter sulfurreducens is a representative electroactive bacterium in many soils,sediments,and wastew-ater systems.It has been confirmed to directly extract electrons from elemental metals.However,little is known about the effect of electron shuttles in G.sulfurreducens corrosion on stainless steel.In this study,we report that exogenous flavins promote iron-to-microbe electron transfer,accelerating micro-bial corrosion.G.sulfurreducens caused 1.3 times deeper pits and increased electron uptake(with 2 times increase of i_(corr))from stainless steel when riboflavin was added to the culture medium.OmcS-deficient mutant data suggest that G.sulfurreducens utilizes riboflavin as a bound-cofactor in outer membrane c-type cytochromes.The finding that,in the presence of microbes,riboflavin can substantially accelerate corrosion highlights the role of flavin redox cycling for enhanced iron-to-microbe electron transfer by G.sulfurreducens and provides new insights in microbial corrosion.

A Semi-Mechanistic Model for Predicting the Service Life of Composite Coatings on VW63Z Magnesium Alloy

The application of Mg alloys is always accompanied by various coating technology, but a reliable model predicting the service life of coatings on Mg alloys is lacking but urgent. In this work, a semi-mechanistic model was proposed to predict the service life of plasma electrolytic oxidation (PEO) coating/electrophoretic coatings on a VW63Z Mg alloy;the model was decomposed into three parts: a first part depicting the degradation time of organic coating (L_(1)) and the diffusion time of electrolyte in the inorganic coating (L_(2)), respectively;a second part interpreting the breakdown of coatings due to the corrosion process (L_(3));a final part establishing an algorithm converting the accelerated tests into the real service environment (α);the effect of structural stress and dissimilar metal joints on the service life of coatings was also considered. Based on the ongoing accelerated experiments, the semi-mechanistic model could be able to predict the service life of both PEO coatings and composite coatings on VW63Z Mg alloy with a satisfiable precision.

High temperature self-lubricating Ti-Mo-Ag composites with exceptional high mechanical strength and wear resistance

Titanium alloys are of keen interest as lightweight structural materials for aerospace and automotive in-dustries.However,a longstanding problem for these materials is their poor tribological performances.Herein,we designed and fabricated a multiphase Ti-Mo-Ag composite(TMA)with heterogeneous triple-phase precipitation(TPP)structure by spark plasma sintering.A lamellarα-phase(αL)precipitates from theβ-phase under furnace cooling conditions and maintains a Burgers orientation relationship(BOR)withβ-matrix.An active eutectic transition also occurs in the titanium matrix,resulting in TiAg phase.The intersecting acicular TiAg and lamellarαL cutβgrains into fine blocks and the primary equiaxedαphase also provides many interfaces withβphase,which together effectively impede dislocation move-ment and increase strength.Compared with other titanium composites,TMA with TPP microstructure gets an excellent combination of strength(yield strength 1205 MPa)and toughness(fracture strain 27%).Furthermore,the TPP structure endows TMA with strong cracking resistance,which aids in reducing abra-sive debris at high temperatures during sliding and obtaining a low wear rate.Simultaneously,Ag parti-cles distributed at grain boundaries will easily diffuse to the wear surface,in situ forming the necessary lubricating phase Ag_(2)MoO_(4) with Mo-rich matrix debris via oxidation.TMA possesses excellent tribologi-cal properties with especially low wear rate of 8.0 x 10^(-6)mm^(3)N^(-1)m^(-1) and friction coefficient(CoF)of merely 0.20 at 600℃.Unlike other self-lubricating composites with high volume fraction of soft ceramic lubricants,which inevitably sacrifice their mechanical strength and ductility,the composite TMA pos-sesses well-balanced strength,toughness and self-lubricating properties.It holds important implications to design other metal matrix self-lubricating composites(MMSCs)used for load-bearing moving parts.

Investigation of the Corrosion and Passive Behavior of HP-13Cr Stainless Steel in Formate Annulus Protection Fluid

The corrosion and passive behavior of HP-13Cr stainless steel(HP-13Cr SS)in formate annulus protection fluid was investigated.HP-13Cr SS exhibited good passive behavior in clean formate annulus protection fluid,which was attributed to a thinner and more dense passive film mainly composed of Cr_(2)O_(3).In the formation water solution,the passive film was composed of metastable Cr(OH)3,which was explained by the isoelectric point theory,resulting in the deterioration of the passive behavior of HP-13Cr SS.When the formation water penetrated the formate annulus protection fluid,a large number of loose FeCO_(3)particles formed in the corrosion scales,thus HP-13Cr SS suffered severe corrosion.Therefore,avoiding formation water penetrating the formate annulus protection fluid is conducive to improving the service life of HP-13Cr SS oil tubes in extremely aggressive environment.

Corrosion Behavior of Pre-oxidized GH4169 Alloy with Solid NaCI Deposited in a Wet Oxygen Flow at 600 ℃

The corrosion behavior of the pre-oxidized GH4169 alloy was studied after 20 h of exposure under a solid NaCl deposit film in a wet O_(2) environment at 600℃ by mass-gain measurements,X-ray diffraction,scanning electron microscopy,transmission electron microscopy methods.The results indicate that the pre-oxidized GH4169 alloy undergoes serious corrosion in the corrosive condition.The preformed Cr_(2)O_(3) layer is gradually destroyed by deposit NaCl,and the inner Nb2O5 layer beneath the complete outer Cr_(2)O_(3) layer also reacts with NaCl to form NaNbO_(3).The electrochemical test results testified the existence of electrochemical reactions during this corrosion process.The corrosion behavior of pre-oxidized GH4169 under a solid NaCl deposit film in a wet O_(2) environment at 600℃has been discussed in detail.

Simulation and experiment of a transplanting mechanism for sweet potato seedlings with ‘boat-bottom’ transplanting trajectory

Planting on mulched soil is the main cultivation mode for sweet potato slips in spring in northern China.The‘boatbottom’planting method can bring high quantity and similar size for sweet potatoes.In this study,a mechanism for transplanting sweet potato seedlings on mulched was proposed,which could realize‘boat-bottom’transplanting trajectory and improve the planting efficiency.The virtual prototype model of the transplanting mechanism was constructed using ADAMS software,a soil particle model and a flexible body model of sweet potato seedling were established using EDEM software,and then a joint simulation was carried out to find out the interaction of mechanism,seedling and soil.By simulation,the trajectory of the clamping point,the sweet potato seedling posture,soil particles,pits,and relative force were all analyzed,which verified the rationality of the transplanting mechanism design.Finally,three kinds of sweet potato seedlings,watermelon red,Yan-25,and purple sweet potato seedlings were selected,and transplanting experiments were carried out on the mulch to verify that the theoretical trajectory,the simulated trajectory,and the actual trajectory were consistent.The transplanting success rates of the three kinds of sweet potato seedlings were all above 85%,indicating that different varieties of sweet potato seedlings had little effect on the transplanting effect of the mechanism,which reflected that the transplanting mechanism had good practicability and adaptability.

Laser directed energy deposited, ultrafine-grained functional titanium-copper alloys tailored for marine environments: Antibacterial and anti-microbial corrosion studies

The microorganism-rich nature of the ocean imposes great challenges to the structural integrity of met-als over their service lifespan,including titanium(Ti)alloys,which are usually prone to microbiologically influenced corrosion(MIC).So,multifunctional anti-MIC Ti alloys need to be developed and studied.This paper investigates the effect of copper(Cu)concentration on the MIC resistance of a series of additively manufactured,ultrafine-grained Ti-x Cu(x=3.5,6.5 and 8.5 in wt.%)alloys.The dependence of the cor-rosion resistance and MIC resistance on the Cu concentration of Ti-Cu alloy is interpreted considering all conceivable mechanisms.The mechanisms for excellent corrosion resistance of Ti-Cu alloy in seawater are attributed to the strong passive film and small surface potential difference between phases.Microstruc-tural characterization reveals that uniformly distributed,nanosized Ti_(2) Cu phase led to increased reactive oxygen species in the bacterial membrane,which is the root reason for the superb anti-bacterial property(99.2%)for Ti-8.5Cu.Compared to pure Ti and Ti-6Al-4V,Ti-8.5Cu alloy features both high strength(yield stress>1000 MPa)and the best MIC resistance(97.5%).The combination of such balanced properties enables this functional 3D printed Ti-Cu alloy to become an ideal material for load-bearing applications in the marine environment.

On the rumpling mechanism in nanocrystalline coatings:Improved by reactive magnetron sputtering with oxygen

Surface rumpling is detrimental to high temperature protective coatings as it shortens their lifetime and leads to adhesion losses and unexpected corrosion degradation.The driving force and mass transport mechanism behind of rumpling remains to be clarified.In the present investigation,we subjected two types of nanocrystalline coating systems to avoid the influence of interdiffusion on rumpling study.One group was an ordinary nanocrystalline coating,and the other group was designed and prepared with trace oxygen by reactive magnetron sputtering.Systematic cyclic oxidation test at 1100°C was also car-ried out.Results show the ordinary nanocrystalline coating oxidized rapidly,which leads to the fast consumption of Al and the acceleration of phase transition in the coating.Meanwhile,severe surface rumpling is observed due to the stress release of nanocrystals through plastic deformation.Besides,the reactive doping of oxygen can significantly reduce the consumption process of Al in nanocrystalline coat-ing.The rumpling is controlled due to the improvement of coefficient of thermal expansion and Young’s modulus of the coating.Thereafter,the cyclic oxidation resistance is improved.

Enhanced pitting corrosion resistance of CoCrFeMnNi high entropy alloy in the presence of Desulfovibrio vulgaris via nitrogen doping

Corrosion-resistant high nitrogen high entropy alloys(HEAs)were manufactured by pressurized metal-lurgy.This work revealed the inhibitory effect of nitrogen on pitting corrosion of HEAs caused by sul-fate reducing bacterium Desulfovibrio vulgaris.Results indicated that HEA-0 N was susceptible to pitting corrosion and sulfidation under attack of D.vulgaris,whereas the addition of nitrogen significantly de-creased the pitting sensitivity.Pitting potentials of HEA-0.52 N and HEA-1.23 N increased by 133%and 171%,respectively compared to HEA-0 N in the presence of SRB.X-ray photoelectron spectroscopy results unveiled that nitrogen enriched in passive film and strengthened it by increasing fraction of Cr_(2)O_(3)and Fe^(3+)_(ox).Surface of the nitrogen-alloyed HEAs exhibited less defective passive films as revealed by Mott-Schottky results.Nitrogen doping provides a novel insight into the design of microbial corrosion resistant HEA.