Preparation And Performance For The Multiple And Heterogeneous Graphene-enhanced Composite Coating

Surface coating is an important technology for enhancing the anti-corrosion,anti-friction and anti-wear performance of materials.Coating with solo composition or function is dissatisfactory in aggressive environment.Multiple superior properties of composite coatings can be obtained by taking advantage of the diversity of materials and the multiplicity of structures in composite coatings.Graphene and graphene oxides with excellent property of conductivity,specific strength and specific surface area due to the unique two-dimension laminated structure are significant anti-corrosion and anti-wear materials,so,adding graphene into metal coating to enhance the corrosion resistance and wear resistance is strategic.Property of graphene is closely related to its the distribution and concentration.Graphene film on the metal surface is strict with the integrity.The defective graphene film would accelerate the destruction of metal by forming galvanic corrosion.Moreover,the graphene film tends to destroyed and loss from the contact interface during the friction process for the thin thickness and weak cohesion with the substrate.Therefore,constructing graphene into the coating with a special state is key to prepare multiple and heterogeneous graphene-enhanced composite coating with high-performance.Preparation technologies for graphene composite material and coating are crucial to the distribution and performance of graphene.In this work,a Zn-G/Al composite coating and G-LDH composite coating were prepared,the corrosion and wear behavior for the coatings were systematically studied.The characteristics and properties of the coatings were tested by X-Ray diffraction,Scanning electron microscope,Raman spectrum,X-ray photoelectron spectroscopy,electrochemical testing and wear testing.The working mechanism for the multiple heterogeneous graphene-based composite coating has been discussed.The main innovations as follows:(1)The reduced graphene oxide(G)was coated on Al powders(G/Al)by in-situ reduction and then co-deposited with Zn powders on low-carbon steel by low pressure cold sprayed method,the obtained coating is Zn-G/Al coating.The microstructure analysis revealed that G was uniformly distributed among Zn-Al interface.Compared with Zn-Al coating,the self-corrosion potential for Zn-G/Al coating is reduced by 0.244 VSCE and the corrosion current is 16-times increased.In extreme environment,corrosion products with protective ability quickly formed and filled the defect of the coating,which repaired the defect.The repair effect of Zn-G/Al coating can be attributed to the severe galvanic corrosion result from the high conductivity of graphene in the coating,which promote the formation and compaction of the corrosion product layer.(2)Zn-0.2wt.%G/Al coating exhibits has a superior periodic lubrication characteristic and the coefficient of friction is low to 0.2.The periodic lubrication effect of the coating is attributed to G in the interface,which promotes the rapid formation of the lubricating corrosion product layer at the wear marks and repairs the wastage of lubrication layer at the wear marks.(3)The multiple heterogeneous graphene-based composite coating(G-LDH)on Mg alloy was fabricated hydrothermally based on in-situ growth layered double hydroxides(LDH)on pre-cold sprayed G coated Aluminums(G-Al)coating,the characteristics of the coating demonstrated that the graphene contained in the intermediate layer has in-situ transferred into LDH film.The maze blocking effect of G coupled with the inhibition-corrosion of LDH endowed this system with superb anti-corrosion performance.The self-corrosion potential for G-LDH is 0.06 VSCE and 0.29 VSCE higher than that of LDH and G-Al coating.An obvious pitting corrosion was generated on LDH and the value of log|Z|0.01Hz for the coating is down to 5×103 Ω·cm2 after full immersion in 3.5wt.%NaCl solution for 15 days.The protective ability for G-LDH coating still retains with the value of log|Z|0.01Hz at1.994×104 Ω·cm2 and there was no phenomenon of destruction on the surface of G-LDH.(4)The tribological tests demonstrated that the synergistic effect of G and LDH endowed the G-LDH with a lower friction coefficient at 0.2,excellent friction property and load capability.The unique architecture of G anchored LDH film was greatly benefit for the rapid formation of the G-rich hybrid lubrication film,the in-situ growth LDH with strength bonding force with the substrate restrained the excessive removal of the LDH film during the wear process and the strengthening effect of G in the LDH contributes to improved stability and integrity of graphene-LDH lubricating interface on wear scar.