Influence of layer thickness on formation quality,microstructure,mechanical properties,and corrosion resistance of WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion(L-PBF)of Mg alloys has provided tremendous opportunities for customized production of aeronautical and medical parts.Layer thickness(LT)is of great significance to the L-PBF process but has not been studied for Mg alloys.In this study,WE43 Mg alloy bulk cubes,porous scaffolds,and thin walls with layer thicknesses of 10,20,30,and 40μm were fabricated.The required laser energy input increased with increasing layer thickness and was different for the bulk cubes and porous scaffolds.Porosity tended to occur at the connection joints in porous scaffolds for LT40 and could be eliminated by reducing the laser energy input.For thin wall parts,a large overhang angle or a small wall thickness resulted in porosity when a large layer thicknesses was used,and the porosity disappeared by reducing the layer thickness or laser energy input.A deeper keyhole penetration was found in all occasions with porosity,explaining the influence of layer thickness,geometrical structure,and laser energy input on the porosity.All the samples achieved a high fusion quality with a relative density of over 99.5%using the optimized laser energy input.The increased layer thickness resulted to more precipitation phases,finer grain sizes and decreased grain texture.With the similar high fusion quality,the tensile strength and elongation of bulk samples were significantly improved from 257 MPa and 1.41%with the 10μm layer to 287 MPa and 15.12%with the 40μm layer,in accordance with the microstructural change.The effect of layer thickness on the compressive properties of porous scaffolds was limited.However,the corrosion rate of bulk samples accelerated with increasing the layer thickness,mainly attributed to the increased number of precipitation phases.

Greatly enhanced corrosion/wear resistances of epoxy coating for Mg alloy through a synergistic effect between functionalized graphene and insulated blocking layer

The poor corrosion and wear resistances of Mg alloys seriously limit their potential applications in various industries.The conventional epoxy coating easily forms many intrinsic defects during the solidification process,which cannot provide sufficient protection.In the current study,we design a double-layer epoxy composite coating on Mg alloy with enhanced anti-corrosion/wear properties,via the spin-assisted assembly technique.The outer layer is functionalized graphene(FG)in waterborne epoxy resin(WEP)and the inner layer is Ce-based conversion(Ce)film.The FG sheets can be homogeneously dispersed within the epoxy matrix to fill the intrinsic defects and improve the barrier capability.The Ce film connects the outer layer with the substrate,showing the transition effect.The corrosion rate of Ce/WEP/FG composite coating is 2131 times lower than that of bare Mg alloy,and the wear rate is decreased by~90%.The improved corrosion resistance is attributed to the labyrinth effect(hindering the penetration of corrosive medium)and the obstruction of galvanic coupling behavior.The synergistic effect derived from the FG sheet and blocking layer exhibits great potential in realizing the improvement of multi-functional integration,which will open up a new avenue for the development of novel composite protection coatings of Mg alloys.

Tribological behaviors of Fe-Al-Cr-Nb alloyed layer deposited on 45 steel via double glow plasma surface metallurgy technique

Double glow plasma surface metallurgy technique was used to fabricate a Fe?Al?Cr?Nb alloyed layer onto the surface of the 45 steel. The microstructures and composition of th?eA Fl?eCr?Nb alloyed layer were analyzed by scanning electronic microscopy, X-ray diffraction and energy dispersive spectroscopy. The results indicate thatthe 20 μm alloyed layer is homogeneous and compact. The alloyed elements exhibit a gradient distribution along the cross section. Microhardness and nanoindentation tests imply that the surface hardness of the alloyed layer reaches HV 580, which is almost 2.8 times that of the substrate. Compared with the substrate, the alloyed layer has a much smaller displacement and a larger elastic modulus. According to the friction and wear tests at room temperature, the? FeAl?Cr?Nb alloyed layer has lower friction coefficient and less wear mass, implying that the Fe?Al?Cr?Nb alloyed layer can effectively improve the surface hardness and wear resistance of the substrate.

Design of self-healing PEO-based protective layers containing in-situ grown LDH loaded with inhibitor on the MA8 magnesium alloy

The high corrosion rate of magnesium and its alloys in chloride-containing solution significantly reduces the potential of this material for diverse applications.Therefore,the formation of a smart protective coating was achieved in this work to prevent degradation of the MA8 magnesium alloy.A porous ceramic-like matrix was obtained on the material by plasma electrolytic oxidation(PEO).Further surface functionalization was performed using layered double hydroxides(LDH) served as nanocontainers for the corrosion inhibitor.Several methods of LDH intercalation with benzotriazole(BTA) were proposed.The composition and morphology of the formed coating were studied using SEM-EDX analysis,XRD,XPS,and Raman microspectroscopy.The corrosion behavior of the coated samples was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization.The corrosion rate was estimated using volumetry and gravimetry methods.The formed composite coating provides the Mg alloy with the lowest corrosion activity(|Z|_(f)=0.1 Hz)=8.48·10^(5) Ω·cm^(2),I_(c)=1.4·10^(-8)A/cm^(2),P_(H)=0.21 mm/year) and improves the protective properties of the PEO-coated sample(|Z|_(f)=0.1 Hz)=8.37·10^(3) Ω·cm^(2),I_(c)=4.1·10^(-7)A/cm^(2),P_(H)=0.31 mm/year).The realization of the self-healing effect of the inhibitor-containing LDH/PEO-coated system was studied using localized electrochemical methods(SVET and SIET) with two artificial defects on the surface.A mechanism involving three stages for the active corrosion protection of the alloy was proposed.These findings contribute to the follow-up work of developing modified LDH/PEO-based structures that promote the Mg alloy with high corrosion resistance,superior electrochemical performance for applications in various fields of industry and medicine.

Nano silica aerogel-induced formation of an organic/alloy biphasic interfacial layer enables construction of stable high-energy lithium metal batteries

Lithium metal batteries represent promising candidates for high-energy-density batteries, however, many challenges must still be overcome,e.g., interface instability and dendrite growth. In this work, nano silica aerogel was employed to generate a hybrid film with high lithium ion conductivity(0.6 mS cm^(-1)at room temperature) via an in situ crosslinking reaction. TOF-SIMS profile analysis has revealed conversion mechanism of hybrid film to Li–Si alloy/Li F biphasic interface layer, suggesting that the Li–Si alloy and Li F-rich interface layer promoted rapid Li+transport and shielded the Li anodes from corrosive reactions with electrolyte-derived products. When coupled with nickel-cobalt-manganese-based cathodes, the batteries achieve outstanding capacity retention over 1000 cycles at 1 C. Additionally the developed film coated on Li enabled high coulombic efficiency(99.5%) after long-term cycling when coupled with S cathodes. Overall, the results presented herein confirm an effective strategy for the development of high-energy batteries.

Self-assembly of coumarin molecules on plasma electrolyzed layer for optimizing the electrochemical performance of AZ31 Mg alloy

A novel inorganic-organic layer with outstanding corrosion resistance in a 3.5wt.% NaCl solution was fabricated by taking advantage of the unique interactions between coumarin (COM) molecules and the porous layer formed on Mg alloy. To achieve this aim, the AZ31 Mg alloy coated via microarc oxidation (MAO) coating was placed in an ethanolic solution of COM for 6 and 12 h at 25 ℃. By reducing the surface area exposed to the corrosive species, the donor-acceptor complexes produced by the particular interactions between the COM and MAO surface would successfully prevent the corrosion of Mg alloy substrate. The MAO layer would provide the ideal sites for the charge-transfer-induced physical and chemical locking, leading to uneven organic layer nucleation and crystal growth with a thatch-like structure. To evaluate the formation mechanism of such hybrid composites and highlight the key bonding modes between the COM and MAO, theoretical simulations were conducted.

Advances in Mg-Al-layered double hydroxide steam coatings on Mg alloys:A review

Layered double hydroxide(LDH)coatings on magnesium(Mg)alloys shine brightly in the field of corrosion protection because of their special ion-exchange function.State-of-the-art steam coating as a type of LDH film preparation technique has emerged in recent years because only pure water is required as the steam source and its environmentally friendly LDH coating fits the current need for green development.Moreover,this coating can effectively inhibit the corrosion of the Mg alloy substrate due to the chemical bonding between the coating and the Mg alloy substrate.This review systematically explains cutting-edge advancements in the growth mechanism and corrosion behavior of LDH steam coatings,and analyzes the advantages and limitations of the steam-coating method.The influencing factors including pressure,CO_(2)/CO_(3)^(2-),aluminum content of the substrate alloy,solution type,and acid-pickling pretreatment,as well as the post-treatment of steam-coating defects,are comprehensively elucidated,providing new insights into the development of the in situ steam-coating technique.Finally,existing issues and future prospects are discussed to further accelerate the widespread application of Mg alloys.

Improving Corrosion Resistance of Q235 Steel by Ni-Cr Alloyed Layer

Ni-Cr alloyed layer was formed on surface of Q235 steel by double glow plasma surface metallurgy to improve the corrosion resistance of substrate. The composition and microstructure of alloyed layer was analyzed by SEM and XRD. Potentiodynamic polarization and electrochemical impedance spectroscopy was applied to evaluate the corrosion resistance of the alloyed layer. The results showed working pressure had a great effect on structure of Ni-Cr alloyed layer, and the dense and smooth alloyed layer was prepared at 50 Pa working pressure. Compared with substrate, Ni-Cr alloyed layer exhibited higher corrosion potential, lower corrosion current density and larger charge transfer resistance, which indicated that Ni-Cr alloyed layer significantly modified the corrosion resistance of Q235 steel.

Plasma Surface Cu Alloyed Layer as a Lubricant on Stainless Steel Sheet:Wear Characteristics and On-job Performance in Incremental Forming

To solve the problems of poor forming and easy adhesion of the stainless steel,Cu alloyed layer on the stainless steels was prepared by the double glow plasma surface alloying technique.The experimentalresults indicated that the supersaturated copper dispersedly precipitated in grain interior and crystalboundaries and formed the vermicular structure.The tribologicaltests indicated that the friction coefficient of the Cu alloyed layer was lower than that of the stainless steels.The wear rate of stainless steelin the presence of Cu alloyed layer was approximately 2-fold lower than that in the absence of the alloyed layer.The results of the incrementalforming indicated that the ploughing phenomenon was not observed on the stainless steelin the presence of Cu alloyed layer during the incrementalforming,while the stainless steelpresented the deep ploughing.Therefore,Cu alloyed layer on stainless steelexhibited excellent self-lubrication and forming properties.

Lithiophilic Li-Si alloy-solid electrolyte interface enabled by high-concentration dual salt-reinforced quasi-solid-state electrolyte

Solid polymer electrolytes(SPEs)are urgently required to achieve practical solid-state lithium metal batteries(LMBs)and lithium-ion batteries(LIBs),Herein,we proposed a mechanism for modulating interfacial conduction and anode interfaces in high-concentration SPEs by LiDFBOP.Optimized electrolyte exhibits superior ionic conductivity and remarkable interface compatibility with salt-rich clusters:(1)polymer-plastic crystal electrolyte(P-PCE,TPU-SN matrix)dissociates ion pairs to facilitate Li+transport in the electrolyte and regulates Li^(+)diffusion in the SEI.The crosslinking structure of the matrix compensates for the loss of mechanical strength at high-salt concentrations;(2)dual-anion TFSI^(-)_(n)-DFBOP^(-)_(m)in the Li^(+)solvation sheath facilitates facile Li^(+)desolvation and formation of salt-rich clusters and is conducive to the formation of Li conductive segments of TPU-SN matrix;(3)theoretical calculations indicate that the decomposition products of LiDFBOP form SEI with lower binding energy with LiF in the SN system,thereby enhancing the interfacial electrochemical redox kinetics of SPE and creating a solid interface SEI layer rich in LiF.As a result,the optimized electrolyte exhibits an excellent ionic conductivity of9.31×10^(-4)S cm^(-1)at 30℃and a broadened electrochemical stability up to 4.73 V.The designed electrolyte effectively prevents the formation of Li dendrites in Li symmetric cells for over 6500 h at0.1 mA cm^(-2).The specific Li-Si alloy-solid state half-cell capacity shows 711.6 mAh g^(-1)after 60 cycles at 0.3 A g^(-1).Excellent rate performance and cycling stability are achieved for these solid-state batteries with Li-Si alloy anodes and NCM 811 cathodes.NCM 811‖Prelithiated silicon-based anode solid-state cell delivers a discharge capacity of 195.55 mAh g^(-1)and a capacity retention of 97.8%after 120 cycles.NCM 811‖Li solid-state cell also delivers capacity retention of 84.2%after 450 cycles.

Development of anti-corrosive coating on AZ31 Mg alloy modified by MOF/LDH/PEO hybrids

The self-assembly of hybrid inorganic-organic materials on stationary platforms plays a critical role in improving their structural stability and wide usability.In this work,a novel two-step hydrothermal approach is proposed for synthesizing stable and advanced hybrid coatings on metal-oxide platforms through the surface modification of layered double hydroxide(LDH)films using novel metal-organic frameworks(MOFs).Initially,Mg-Al LDH nanocontainers,grown on a magnesium oxide layer produced through plasma electrolytic oxidation(PEO)of AZ31 Mg alloy substrate,were intercalated with cobalt via an oxidation route,providing the metallic coordination center for the MOF formation.In the subsequent step,a pioneering technique is introduced,utilizing tryptophan as the organic linker for the first time at a pH of 10.The self-assembly of cobalt-tryptophan complex,driven by the strong bonding between electrophilic sites of monomers and nucleophilic sites,facilitated the formation of a MOF network having a cloud-like structure on the surface of MgAl LDH's film.The resulting MOF-LDH encapsulation containers demonstrate exceptional electrochemical stability when exposed to a 3.5 wt.%NaCl solution,surpassing the performance of PEO and pure LDH coatings.This enhanced stability is attributed to the development of a dense top layer and a stable composition within the self-assembled MOF,effectively sealing flaws and preventing the infiltration of corrosive ions into the underlying metallic substrate.The formation mechanism of MOFs on LDH galleries is investigated using density functional theory calculations.

Enhancing the anti-corrosion performance and biocompatibility of AZ91D Mg alloy by applying roughness pretreatment and coating with in-situ Mg(OH)_(2)/Mg-Al LDH

Corrosion-resistant and biocompatible films were fabricated on AZ91D Mg alloy substrates by varying their roughness levels using met-allographic preparation and subsequent hydrothermal procedures.The coated films comprised a mixed structure of Mg(OH)_(2)and Mg-Al layered double hydroxides(LDH)and exhibited excellent compactness.Coating film thickness increased with decreasing surface roughness.Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy.Metallographic pretreat-ment influenced the chemical activity of the Mg alloy surface and helped modulate the dissolution rate of the Mg_(17)Al_(12)phase during the hydrothermal procedure.With decreasing roughness of the Mg substrate,the Al^(3+)concentration gradually increased,accelerating the in-situ formation of the Mg(OH)_(2)/LDH composite coating and improving its crystallinity.A thick and dense Mg(OH)_(2)/LDH coating was synthesized on the Mg substrate with the least roughness,substantially improving the corrosion resistance of the AZ91D alloy.The lowest corrosion current density((5.73±2.75)×10^(−8)A·cm^(−2))was achieved,which was approximately three orders of magnitude less than that of bare AZ91D.Moreover,the coating demonstrated biocompatibility with no evident cytotoxicity,cellular damage,and hemolytic phenomena.This study provides an effective method for preparing coatings on Mg alloy surfaces with excellent corrosion resistance and biocompatibility.

Dual-function protective layer for highly reversible Zn anode

The thermodynamic instability of zinc anodes in aqueous electrolytes leads to issues such as corrosion,hydrogen evolution reactions(HER), and dendrite growth, severely hindering the practical application of zinc-based aqueous energy storage devices. To address these challenges, this work proposes a dualfunction zinc anode protective layer, composed of Zn-Al-In layered double oxides(ILDO) by rationally designing Zn-Al layered double hydroxides(Zn-Al LDHs) for the first time. Differing from previous works on the LDHs coatings, firstly, the ILDO layer accelerates zinc-ion desolvation and also captures and anchors SO_(4)^(2-). Secondly, the in-situ formation of the Zn-In alloy phase effectively lowers the nucleation energy barrier, thereby regulating zinc nucleation. Consequently, the zinc anode with the ILDO protective layer demonstrates long-term stability exceeding 1900 h and low voltage hysteresis of 7.5 m V at 0.5 m A cm^(-2) and 0.5 m A h cm^(-2). Additionally, it significantly enhances the rate capability and cycling performance of Zn@ILDO//MnO_(2) full batteries and Zn@ILDO//activated carbon zinc-ion hybrid capacitors.This simple and effective dual-function protective layer strategy offers a promising approach for achieving high-performance zinc-ion batteries.

Influence of the Electrode Distance on Microstructure and Corrosion Resistance of Ni-Cr Alloyed Layers Deposited by Double Glow Plasma Surface Metallurgy

Ni-Cr alloyed layers were synthesized on the surface of Q235 mild steel by double-glow plasma surface metallurgy with different electrode distance.The microstructure and phases of the alloyed layer were characterized by scanning electron microscopy(SEM),energy dispersive X-ray spectrometry(EDS),and X-ray diffraction(XRD).The corrosion behavior of the Ni-Cr alloyed layers both in 3.5%NaCl and 0.5 M H_(2)SO_(4) solution were systematically investigated by open-circuit potential(OCP),potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The obtained results reveal that the Ni-Cr alloyed layer consists of a deposited layer and an inter-diffusion layer.With increasing the electrode distance,the relative thickness,microstructure and phase composition of the Ni-Cr alloyed layers vary greatly.Polarization data show the Ni-Cr alloyed layer with the electrode distance of 15 mm has highest corrosion resistance and lowest corrosion rate,while EIS results reveal the same trend.The highest protective efficiency in 3.5%NaCl and 0.5 M H_(2)SO_(4) solution are 99.23%and 99.92%,respectively,obtained for the Ni-Cr alloyed layer with 15 mm electrode distance.When the electrode distance is too large,a thin and porosity Ni-Cr alloyed layer,caused by low plasma density and Kirkendall effect,will be obtained,and will decrease the protective efficiency in corrosive medium.

Effects of reflowing temperature and time on alloy layer of tinplate and its electrochemical behavior in 3.5%NaCl solution

Effects of reflowing temperature and time on the alloy layer of tinplate and its electrochemical behavior in 3.5%NaCl solution were investigated by electrochemical measurements and surface characterization.It is found that the amount of alloy layer increases with the increase of reflowing temperature and time.Then the corrosion potential of detinned tinplate shifts positively and the corrosion rate decreases.After being coupled with tin,the detinned tinplate acts as cathode and tin acts as anode initially.However,after being exposed for some time,the potential shifts of both detinned tinplate and tin reverse the polarity of the coupling system.The galvanic current density decreases with the increase of reflowing temperature and time.

Structure and effects of electroless Ni-Sn-P transition layer during acid electroless plating on magnesium alloys

An electroless ternary Ni-Sn-P transition layer with high corrosion resistance was applied for acid electroless nickel plating on magnesium alloys. The surface morphologies and microstructure of the traditional alkaline electroless Ni-P and novel Ni-Sn-P transition layers were compared by SEM and XRD, and the bonding strengths between the transition layers and AZ31 magnesium alloys were tested. The corrosion resistance of the samples was analyzed by porosity test, potentiodynamic polarization, electrochemical impedance spectroscopy（EIS） in acid electroless solution at p H 4.5 and immersion test in 10% HCl. The results indicate that the transition layer is essential for acid electroless plating Ni-P coatings on magnesium alloys. Under the same thin thickness（-6 μm）, the electroless Ni-Sn-P transition layer possesses superior properties to the traditional Ni-P transition layer, including high amorphization, smooth and dense surface without pores, enhanced bonding strength and corrosion resistance. Most importantly, acid electroless Ni-P coatings can be successfully deposited on magnesium alloys by using Ni-Sn-P transition layer.

Effects of grain size on shift of neutral layer of AZ31 magnesium alloy under warm condition

The effects of grain size on the shift of neutral layer of AZ31 magnesium alloy sheets with different grain sizes ranging from 12.1 to 34.7μm were investigated by the 90° V-bending tests at 150 °C. The results show that the neutral layer tends to shift to outer region of the sheets and the coefficient of neutral layer value (k-value) increases with the increasing grain size. This phenomenon is mainly owing to the enhanced asymmetry between the outer tension region and inner compression region with the increase of grain size. Twinning dominates the deformation in inner region while slips dominate the deformation in outer region.

Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg-Al layered double hydroxide coating

To further enhance the corrosion resistance of the porous micro-arc oxidation(MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg-Al layered double hydroxide(LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.

Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with copper interlayer sheet

Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with a copper sheet as interlayer was carried out.Microstructures of the joint were studied by optical microscopy(OM),scanning electron microscopy(SEM) and X-ray diffractometry(XRD).In addition,the mechanical properties of the joint were evaluated by tensile test and the microhardness was measured.These two alloys were successfully welded by adding copper transition layer into the weld.Solid solution with a certain thickness was located at the interfaces between weld and base metal in both sides.Regions inside the weld and near the stainless steel were characterized by solid solution of copper with TiFe2 intermetallics dispersedly distributed in it.While weld near titanium alloy contained Ti-Cu and Ti-Fe-Cu intermetallics layer,in which the hardness of weld came to the highest value.Brittle fracture occurred in the intermetallics layer when the joint was stretched.

Effects of alloy elements on microstructure and crack resistance of Fe-C-Cr weld surfacing layer

Effects of alloy elements on the microstructure and crack resistance of Fe-C-Cr weld surfacing layer were investigated. The results show that microstructures of the layer mainly consist of carbides and austenite matrix. Increasing C and Cr contents impair the crack resistance of the layer due to increased amount of brittle carbides. The addition of Ni, Nb or Mo improves the crack resistance of Fe-C-Cr weld surfacing layer by increasing the amount of austenite and forming fine NbC or M 7C 3 carbides in the layer. But, the excessive Nb (>2.50wt%) or Mo (>1.88wt%) impairs the crack resistance of the layer, which has relation with increased carbides or carbide coarsening and austenite matrix solid solution strengthening. The proper combination of C, Cr, Ni, Nb and Mo can further improve not only the crack resistance of Fe-C-Cr weld surfacing layer but also the erosion resistance as a result of fine NbC and M 7C 3 carbides distributing uniformly in austenite matrix. The optimal layer compositions are 3.05wt%C, 20.58wt%Cr, 1.75wt%Ni, 2.00wt%Nb and 1.88wt%Mo.