Corrosion resistance and anti-soiling performance of micro-arc oxidation/graphene oxide/stearic acid superhydrophobic composite coating on magnesium alloys

Magnesium(Mg)alloys,the lightest metal construction material used in industry,play a vital role in future development.However,the poor corrosion resistance of Mg alloys in corrosion environments largely limits their potential wide applications.Therefore,a micro-arc oxidation/graphene oxide/stearic acid(MAO/GO/SA)superhydrophobic composite coating with superior corrosion resistance was fabricated on a Mg alloy AZ91D through micro-arc oxidation(MAO)technology,electrodeposition technique,and self-assembly technology.The composition and microstructure of the coating were characterized by scanning electron microscopy,X-ray diffraction,energy dispersive spectroscopy,and Raman spectroscopy.The effective protection of the MAO/GO/SA composite coating applied to a substrate was evaluated using potentiodynamic polarization,electrochemical impedance spectroscopy tests,and salt spray tests.The results showed that the MAO/GO/SA composite coating with a petal spherical structure had the best superhydrophobicity,and it attained a contact angle of 159.53°±2°.The MAO/GO/SA composite coating exhibited high resistance to corrosion,according to electrochemical and salt spray tests.

ZIF-8-based micro-arc oxidation composite coatings enhanced the corrosion resistance and superhydrophobicity of a Mg alloy

Mg alloys are considered the most promising engineering materials because of their unique properties.However,the uncontrolled corrosion rate of these alloys limits their applications.Therefore,in this study,a micro-arc oxidation layer was used as a transition layer to“directly”grow a zinc-based metal-organic framework(MOF)composite coating on the surface of a Mg alloy(AZ91D).Herein,the two zeolitic imidazolate framework(ZIF-8)coatings with different morphologies were separately prepared by homologous metal oxide induction and a one-step in-situ growth method.The superhydrophobic composite coating showed strong hydrophobicity and self-cleaning properties,which could prevent the penetration of water and corrosive ions(Cl^(−))into the surface of AZ91D.Electrochemical tests demonstrated that the super-hydrophobic composite coatings greatly enhanced the corrosion resistance of AZ91D,and the corrosion current density decreased from 10^(−5)to 10^(−9)A/cm^(2).These results indicate that the ZIF-8 coatings are beneficial for improving the hydrophobicity and enhancing the corrosion resistance of Mg alloys.Therefore,MOF composite coatings provide a new strategy that can be used to prepare multifunctional anticorrosion coatings on metal substrates.

Microstructure and properties of induction brazing nickel base/WC composite coating

BNi-2/WC composite wear-resisting coating was prepared on carbon steel by the method of induction brazing.The microstructure and phase composition of the composite coating were analyzed,and the bonding strength and wear-resisting performance of the coating were tested.During the process of induction brazing,the tungsten carbide partially dissolves and reacts with the filler metal alloy to form NiW compound phase,which realizes the metallurgical combination of tungsten carbide and filler metal alloy.The matrix of the filler metal alloy consists of Ni solid solution and Ni_(3)B/Ni_(3)Si eutectic phase,and the metallurgical diffusion reaction occurs between the filler metal alloy and the steel matrix.The mechanical analysis results show that the self-strength of the composite coating reaches 140 MPa and the bonding strength of the filler metal alloy to the steel matrix reaches 360 MPa.The dry sand rubber wheel wear testing machine showed that the coating weight loss was only 0.2824 g,which was only 1/5 of the weight loss of 65 Mn matrix under the same conditions.

New superhydrophobic composite coatings on Mg-Mn-Ce magnesium alloy

A novel combined method for the formation of composite coatings on the Mg-Mn-Ce alloy is developed.Ceramic like matrix was formed on the Mg alloy surface by the plasma electrolytic oxidation.Then the samples were subsequently processed by dip-coating in an alcohol suspension of superdispersed polytetrafluoroethylene and spraying with the tetrafluoroethylene telomers solution.SEM,OSP,and SPM was used to study structure of formed surfaces.It was established by measurements of CA and CAH,as well as surface free energy calculations that formed coatings demonstrate superhydrophobic properties due to the presence of an irregular hierarchical surface structure and low surface free energy of fluoropolymers.The coating preserves its hydrophobic properties after exposure to high and low temperatures,for a long time as well as being in corrosive environments.EDS and XRD data analysis confirmed the presence of organofluorine compounds in the composite layers,including in the form of crystalline polytetrafluoroethylene.Using potentiodynamic polarization test and EIS,it was found that the resulting coatings significantly increase the corrosion resistance of Mg material.These data are also confirmed by salt spray tests for 40 days.Incorporation of fluoropolymers additionally decrease coatings coefficient of friction.

One-step hydrothermal synthesis of 2,5-PDCA-containing MgAl-LDHs three-layer composite coating with high corrosion resistance on AZ31

The addition of 2,5-pyridinedicarboxylic acid(2,5-PDCA)to the Mg-Al LDH coating,which was prepared by one-step hydrothermal synthesis,had extremely enhanced the corrosion protection of AZ31 Mg alloy,although the 2,5-PDCA could not be intercalated into the interlayer spacing.The corrosion current density of 0.05 mol L^(−1)2,5-PDCA LDH containing LDH coating is 3.18 nA cm^(−2),reduced by two orders of magnitude compared to the LDH coating without inhibitor,and the corrosion inhibition efficiency of the coating is 98.05%.The coating formed on the surface of AZ31 was peeled off from the substrate by using a mechanical method and SEM observation of the cross-section showed that the coating consisted of three different layers.The innermost layer is a thick layer that consists of Mg(OH)_(2)and the intermediate layer is LDH,which is vertical to the substrate and the outmost layer is a thin but very dense deposit layer of LDH agglomerates with complexes of 2,5-PDCA and Mg.This kind of sediment/LDH/Mg(OH)_(2)three-layer composite structure was accountable for the increase in the corrosion resistance of AZ31 Mg alloy.

Corrosion behavior of composite coatings containing hydroxyapatite particles on Mg alloys by plasma electrolytic oxidation: A review

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.

Oxidation and Electrical Properties of Cu-Mn_(3)O_(4)Composite Coating Obtained by Electrodeposition on SOFC Interconnects

Cu-Mn_(3)O_(4)composite coating was prepared on the SUS 430 ferritic stainless steel by electrodeposition and then exposed in air at 800℃corresponding to the cathode atmosphere of solid oxide fuel cell(SOFC).A dual-layer oxide structure mainly comprising an external layer of CuO followed by(Cu,Mn,Fe)_(3)O_(4)spinel and an internal layer of Cr-rich oxide was thermally developed on the coated steel.The scale area-specific resistances(ASRs)of the coated steels were lower than the scale ASR of the uncoated steel after identical thermal exposure.The external layer of CuO/(Cu,Mn,Fe)_(3)O_(4)spinel not only served as a barrier to reduce the growth rate of Cr-rich oxide internal layer and to suppress the outward diffusion of Cr,but also lowered the surface scale ASRs considerably.

Tribological properties of Ni-base alloy composite coating modified by both graphite and TiC particles

In order to reduce the friction coefficient of Ni-base alloy coating and further improve its wear resistance,Ni-base alloy composite coatings modified by both graphite and TiC particles were prepared by plasma spray technology on the surface of 45 carbon steel.The results show that friction coefficient of the composite coating is 47.45% lower than that of the Ni-base alloy coating,and the wear mass loss is reduced by 59.1%.Slip lines and severe adhesive plastic deformation are observed on the worn surface of the Ni-base alloy coating,indicating that the wear mechanisms of the Ni-base alloy coating are multi-plastic deformation wear and adhesive wear.A soft transferred layer abundant in graphite and ferric oxide is developed on the worn surface of the composite coating,which reduces the friction coefficient and wear loss in a great deal.The main wear mechanism of the composite coating is fatigue delamination of the transferred layer.

Tribological properties of nanostructured Al_2O_3-40%TiO_2 multiphase ceramic particles reinforced Ni-based alloy composite coatings

The Ni-based alloy composite coatings reinforced by nanostructured Al2O3-40%TiO2 multiphase ceramic particles were prepared on the surface of 7005 aluminum alloy by plasma spray technology. The microstructure and tribological properties of the composite coatings were researched. The results show that the composite coatings mainly consist of γ-Ni, α-Al2O3, γ-Al2O3 and rutile-TiO2 etc, and exhibit lower friction coefficients and wear losses than the Ni-based alloy coatings at different loads and speeds. The composite coating bears low contact stress at 3 N and its wear mechanism is micro-cutting wear. As loads increase to 6-12 N, the contact stress is higher than the elastic limit stress of worn surface, and the wear mechanisms change into multi-plastic deformation wear, micro-brittle fracture wear and abrasive wear. With the increase of speeds, the contact temperature of worn surface increases. The composite coating experiences multi-plastic deformation wear, fatigue wear and adhesive wear.

Preparation and tribological performances of Ni-P-multi-walled carbon nanotubes composite coatings

Multi-walled carbon nanotubes （MWNTs） were wet-milled in the presence of ammonia and cationic surfactant and then used as reinforcements to prepare Ni-P-MWNTs composite coatings by electroless plating. The tribological performances of the composite coatings under dry condition were investigated in comparison with 45 steel and conventional Ni-P coating, Micrographs show that short MWNTs with uniform length and open tips were obtained through the wet-milling process. The results of wear test reveal that the Ni-P-MWNTs composite coatings posses much better friction reduction and anti-wear performances when compared with 45 steel and Ni-P coating. Within the MWNTs content range of 0.74%-1.97%, the friction coefficient and the volume wear rate of the composite coatings decrease gradually and reach the minimum values of 0.08 and 6.22x10-15 m3/（N.m）, respectively. The excellent tribological performances of the composite coatings can be attributed to the introduction of MWNTs, which play both roles of reinforcements and solid lubricant during the wear process.

Reactive HVOF sprayed TiN-matrix composite coating and its corrosion and wear resistance properties

TiN-matrix composite coating was prepared on 45# steel by reactive high-velocity oxy-fuel （HVOF） spraying. Its microstructure, phase composition, micro-hardness, corrosion resistance in 3.5% NaC1 solution and wear resistance were analyzed. The results suggest that the TiN-matrix composite coating is well bonded with the substrate. The micro-hardness measured decreases with the increase of applied test loads. And the micro-hardness of the coating under heavy loads is relatively high. The TiN-matrix composite coating exhibits an excellent corrosion resistance in 3.5% NaC1 solution. The corrosion potential of coating is positive and the passivation zone is broad, which indicates that the TiN-matrix composite coating is stable in the electrolyte and provides excellent protection to the substrate. The wear coefficient of the coating under all loads maintains at 0.49-0.50. The wear mechanism of the coating is revealed to be three-body abrasive wear. Yet the failure forms of TiN-matrix composite coating under different loads have an obvious difference. The failure form of coating under light loads is particle spallation due to the stress concentration while that of coating under heavy loads is crackin~ between inter-lamellae.

Electrodeposition and corrosion resistance of Ni-P-TiN composite coating on AZ91D magnesium alloy

In order to improve the corrosion resistance and microhardness of AZ91D magnesium alloy, TiN nanoparticles were addedto fabricate Ni-P-TiN composite coating by electrodeposition. The surface, cross-section morphology and composition wereexamined using SEM, EDS and XRD, and the corrosion resistance was checked by electrochemical technology. The results indicatethat TiN nanoparticles were doped successfully in the Ni-P matrix after a series of complex pretreatments including activation, zincimmersion and pre-electroplating, which enhances the stability of magnesium alloy in electrolyte and the adhesion betweenmagnesium alloy and composite coating. The microhardness of the Ni-P coating increases dramatically by adding TiN nanoparticlesand subsequent heat treatment. The corrosion experimental results indicate that the corrosion resistance of Ni-P-TiN compositecoating is much higher than that of uncoated AZ91D magnesium alloy and similar with Ni-P coating in short immersion time.However, TiN nanoparticles play a significant role in long-term corrosion resistance of composite coatings.

Tribological behavior and mechanisms of graphite/CaF_2/TiC/Ni-base alloy composite coatings

In order to reduce the friction coefficients and improve the wear resistance of mechanical parts, which work in the severe friction and wear conditions at heavy loads, the graphite/CaFg/TiC/Ni-base alloy composite coatings were prepared by plasma spray and their tribological behavior and mechanisms were investigated. The results show that the friction coefficients of the composite coatings are in the range of 0.22-0.288, which are reduced by 25.9% to 53% compared with those of the pure Ni-base alloy coatings, and the wear rates of the former are 18.6%-70.1% less than those of the latter. When wear against GCr15 steel balls, a transferred layer mainly composed of ferric oxides, graphite and CaF2 may gradually develop on the worn surface of the composite coatings, which made the friction and wear between GCr15 steel ball and the composite coatings change into that between the former and the transferred layer. So the friction coefficients and the wear lubrication effect of the transferred layer. The main wear layer in friction process. rates of the composite coatings are greatly reduced because of the solid mechanism of the composite coatings is delamination of the transferred

Effects of graphite content on microstructure and tribological properties of graphite/TiC/Ni-base alloy composite coatings

In order to reduce the friction coefficients and further improve the anti-wear properties of Ni-base alloy coatings reinforced by TiC particles,graphite/TiC/Ni-base alloy（GTN） coatings were prepared on the surface of 45 carbon steel.The effects of graphite content on the microstructure and tribological properties of the GTN coatings were investigated.The results show that the addition of graphite to the GTN coatings may greatly reduce the friction coefficients and improve their wear resistance.The 6.56GTN and 12.71GTN coatings exhibit excellent integrated properties of anti-friction and wear resistance under low and high loads,respectively.Under a low load,the wear mechanisms of the GTN coatings are mainly multi-plastic deformation with slight abrasive wear and gradually change into mixture of multi-plastic deformation,delamination and micro-cutting wear with the increase of graphite fraction.As the load increases,the main wear mechanisms gradually change from micro-cracks,micro-cutting and adhesive wear to micro-cutting and micro-fracture with the increase of graphite fraction.

Tribological properties and wear prediction model of TiC particles reinforced Ni-base alloy composite coatings

TiC particles reinforced Ni-based alloy composite coatings were prepared on 7005 aluminum alloy by plasma spray. The effects of load, speed and temperature on the tribological behavior and mechanisms of the composite coatings under dry friction were researched. The wear prediction model of the composite coatings was established based on the least square support vector machine (LS-SVM). The results show that the composite coatings exhibit smaller friction coefficients and wear losses than the Ni-based alloy coatings under different friction conditions. The predicting time of the LS-SVM model is only 12.93%of that of the BP-ANN model, and the predicting accuracies on friction coefficients and wear losses of the former are increased by 58.74%and 41.87%compared with the latter. The LS-SVM model can effectively predict the tribological behavior of the TiCP/Ni-base alloy composite coatings under dry friction.

Effect of wear conditions on tribological properties of electrolessly-deposited Ni-P-Gr-SiC hybrid composite coating

The friction and wear properties of the electrolessly-deposited Ni-P-Gr-SiC composites were investigated. The effects of graphite content, load and rotation speed on the friction coefficient and wear resistance of the composite coatings were mainly investigated. The worn surface and cross section of the coatings were characterized by scanning electron microscopy and energy-dispersive X-ray analysis. The results show that the composite coatings reveal good antifriction and wear resistance due to the synergic effect of graphite and SiC particles. The formation of graphite-rich mechanically mixed layer （GRMML） on the surface of Ni-P-Gr-SiC coating contributes to the good tribological behavior of the wear counterparts and SiC particles play a load bearing role in protecting GRMML from shearing easily.

Tribological behavior and mechanism of NiCrBSi-Y_2O_3 composite coatings

The NiCrBSi-Y2O3 composite coatings were prepared on the surface of 45 carbon steel by plasma spray, the microstructure and tribological properties of the coatings were investigated. The results show that the NiCrBSi-Y2O3 composite coatings are mainly composed of γ-Ni, CrB, Cr7C3 and Y2O3. With addition of Y2O3, hard phases such as CrB, Cr7C3 emerge in composite coating, and the density of the composite coatings also increases. The NiCrBSi-0.5Y2O3 composite coating presents excellent tribological properties. Its friction coefficient is 0.175, which is about 37% of that of the pure NiCrBSi coating. The mass wear loss is 1.2 mg, which is reduced by 43% compared with the pure NiCrBSi coating. When the loads are 6-10 N, the NiCrBSi-0.5Y2O3 composite coating suffers from slight wear and the wear mechanisms are mainly adhesive wear accompany with slight micro-cutting wear and micro-fracture wear. As the load increases to 12 N, the wear mechanisms are adhesive wear and severe micro-cutting wear.

Preparation of Al_2O_3/Au nano-laminated composite coatings and their oxidation resistance on stainless steel

Al2O3/Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al2O3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al2O3/Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.

In-situ synthesis of Al_3Ti particles reinforced Al-based composite coating

Using titanium wires （99.5%, 200 μm in diameter） as a reactive source, an Al-based composite coating reinforced by titanium tri-aluminide （A13Ti） particles was fabricated by infiltration plus in-situ methods. According to the differential thermal analysis （DTA） curve, the reactive temperature between Ti wires and A1 matrix can be determined at 890 ℃. The obtained composite coatings were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and microhardness and wear test. The experimental results show that when holding period is 20 min at 890℃, the titanium wires react completely to in-situ synthesize Al3Ti particles, which presents blocky and strip-like states. The microhardness of in-situ synthesized Al3Ti particles is about 4.5 times that of the Al-matrix. Under the condition of dry sliding at 10 N load, compared with the unreinforced Al matrix, the composite coating fabricated with 20 min offers unique wear resistance behavior, and its wear mechanism is that the adhesive wear and abrasive wear coexist.

Effect of ball peening of substrate on microstructure, phase evolution and properties of electrophoretically deposited YSZ/(Ni,Al) composite coatings

YSZ/（Ni, Al） composite coatings were deposited on Inconel600 superalloy with ball peening （BP） and without （non BP）treatment using the electrophoretic deposition （EPD） technique, followed by vacuum sintering method. The structures and phaseevolution of the coatings were studied with X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy dispersivespectrometry （EDS）. The relation between microstructures and properties of the BPs-coated samples was discussed. The results showthat the adhesion strength and gain mass of the BPs-coated samples with isothermal oxidation at 1100℃ for 100 h are 3.3 N and0.00817 mg/cm^2, respectively, while those of the non-BPs-coated sample are 2.6 N and 0.00559 mg/cm^2, respectively. The EDSmapping analysis indicates that an obvious outward diffusion of Cr from the substrate to BPs coated samples occurs after isothermaloxidation. The BPs-coated sample shows the superior adhesion and oxidation resistance compared with non-BPs-coated samples.