Preparation And Properties Of Ni-based Composite Coatings Reinforced By Functional Graphene

Graphene materials,including graphene(Gr)and its derivative graphene oxide(GO),possess high strength,good electrical conductivity,excellent anti-permeability and self-lubrication characteristic and so on.As the ideal reinforcement,graphene materials are becoming the research hotspot in the field of metal matrix coatings and have a great application prospect.At present,the electrodeposition and the surface coating technology using the high-energy beam have been two important methods to preparing graphene materials reinforced metal matrix composite coatings.However,there are still some problems to be solved in the research and application,such as the agglomeration,the poor compatibility,the decomposition and even burning damage of graphene materials at high temperature.Therefore,in this paper,the electrodeposition and laser cladding were selected as two representive techniques to preparate metal coatings.The research focused on on the magnetic functional treatment and the design and fabrication of metal protective layer on the surface of graphene materials,external magnetic field controlling,the development of in-situ synthesized Gr process and the analysis of tribological and electrochemical properties.In addition,the improving mechanism of the microstructure uniformity and performance of composite coatings by functionalized graphene materials was revealed.And the problems such as the uneven distribution of graphene materials in composite coatings,poor compatibility with metal and easy destruction of structure were solved.Furthermore,the controllable preparation of metal matrix composite coatings reinforced by graphene materials with good tribological property and corrosion resistance was realized.GO reinforced Ni-based electrodeposited composite coatings with pore-free and compact structure as well as high deposition rate were obtained by adding appropriate concentration of GO in plating solution.GO nanosheets were uniformly deposited in the composite coatings owing to their good dispersion stability.Additionally,due to the excellent physical barrier characteristic of GO,the corrosion resistance of composite coatings was significantly improved.The solution strengthening and grain refinement strengthening caused by the co-deposition of GO and Ni atoms were the main factors to increase the micro-hardness of composite coatings.During the electrodeposition process,GO was reduced to the reduced graphene oxide(rGO).The lamellar structure of rGO was easier to withstand external forces,therefore,the composite coatings exhibited lower and stable friction coefficient values.GO nanosheets supported nanoscale magnetic metal particles were prepared using the chemical modification method.As the core carrier,the magnetic CoFe@Gr composite powders were directional arrayed along the direction that parallel to the magnetic induction line,with the help of magnetic field assisted electrodeposition technique.Simultaneously,the co-deposition between CoFe@Gr and Ni atoms occured to form a new Ni-based composite coating with compact and uniform “stripe-like” microstructure.The composite coating presented environmental adaptive function.After two weeks exposure in the atmosphere,the hydrophilicity of the fresh surface changed spontaneously to hydrophobicity,which further enhanced the corrosion resistance of the electrodeposited Ni-based composite coatings reinforced by GO.CoFe@Gr reinforced laser cladded Ni-based composite coatings without porosity defects,uniform microstructure and excellent properties were obtained by preparing dense metal protective coating on Gr surface via the chemical modification method.After laser cladding,Gr nanosheets were mainly in lamellar and twined morphologies preserved in composite coatings.Meanwhile,part of Gr nanosheets were transformed into the nano spherical structure and the “core-shell” structure together with the second phase.These carbon nanostructures significantly improved the tribological performance of composite coatings.Besides,the addition of CoFe@Gr promoted the uniform distribution and the smooth morphology of the second phases,greatly improving the micro-hardness and the compressive strength of composite coatings.The existence of protective coating on Gr surface increased the content of Gr with intrinsic structure retained in composite coatings,which made the diffusion channel of corrosive medium complicate and effectively promoted the corrosion protection effect of composite coatings.Using graphite with thin layer as the precursor,Ni60-Gr mixed powders that multilayer Gr in-situ synthesized on the surface of Ni60 powders were obtained by ultrasonic dispersion coupling mechanical exfoliation.This provided a new idea for the preparation of Gr reinforced laser cladded coatings with good formability.Gr formed by in-situ exfoliating graphite could be preserved in laser cladded coatings and exerted strong capacity of adsorbing metal atoms,therefore,resulting in the formation of two solid solution phases in the composite coatings,including the Fe/Cr-rich body centered cubic solid solution and the Ni-rich face centered cubic solid solution,respectively.Moreover,adding Gr promoted the second phase dispersed through the coating matrix.Due to the effects of second phase dispersion strengthening and thermal mismatch strengthening,Gr reinforced laser cladded Ni-based composite coatings possessed high micro-hardness and good tribological performance.