Research On Microstructure And Properties Of Laser Cladding Nickel-Based Graphene Composite Coating

In order to further improve the wear resistance and corrosion resistance of nickel-based alloys,and improve their work adaptability and service life in various industrial fields,various kinds of high-performance reinforcing phases are usually added to nickel-based alloys to obtain excellent surface properties..As a new star in the family of carbon nanomaterials,graphene has become a research hotspot of enhancement phases with its unique two-dimensional structure and excellent mechanical properties.However,when graphene is directly added to the alloy powder,the high-energy-density laser beam and the high-temperature action of the molten pool can easily destroy the original structure of graphene.This problem hinders the development of graphene-enhanced metal-based composite coatings.In this paper,graphene nanosheets are added to the nickel-based alloy as a reinforcing phase,and the structure and properties of the nickel-based graphene composite coating are specifically studied.In this paper,the nickel-based powder SD-Ni45 made by the research group is selected as the basic powder,and graphene nanoplatelets(GNPs)are added as the reinforcing phase to the SD-Ni45 powder.Before introducing GNPs,it needs to be pretreated by electroless nickel plating to obtain nickel-plated graphene nanosheets(NiGNPs),that is,a nickel protective layer is plated on the outer surface of GNPs to reduce the impact of high-energy laser beams on GNPs in the molten pool.The direct exposure to avoid the destruction of its original structure.During the purification process,the density of defects in the GNPs structure increases,which increases the surface roughness of the GNPs,which lays the foundation for the subsequent nickel plating to provide a strong bond with the coating.After the sensitization and activation process,the surface of GNPs is loaded with reactive sites required for nickel plating.After the GNPs are nickel-plated,the surface is covered with a uniform nickel plating layer with a thickness of about 0.94μm or more.The weight of graphene nanosheets after nickel plating is about 12～15g,an increase of about 60 times.It can be calculated that the content of GNPs in NiGNPs is about 1.3%～1.7%.The NiGNPs with different contents are mixed with SD-Ni45 powder,and the nickel-based composite coatings with different contents of NiGNPs are obtained by laser cladding technology,and then the structure and performance are studied.Studies have found that GNPs are protected by the nickel-plated layer.After the laser cladding process,most of the GNPs in the composite coating can maintain their original structure,but there will still be a small part of GNPs that will occur under the high temperature of the molten pool.Melting,the C atoms formed by the melting will combine with the strong carbide elements in the cladding layer,such as Cr elements,to form carbides,which will have a certain impact on the structure and performance of the composite coating.Under the irradiation of the laser beam,the defect density of GNPs in the composite coating increases,but the structure and distribution are relatively uniform.The addition of GNPs will inhibit the growth of columnar crystals,the structure of the cladding layer will be significantly refined,the number of Cr carbides has increased,and its shape has gradually changed from square,triangle-like,and long strips to large rods and bars.The flaky and eutectic structure no longer presents a fine mesh,but gradually presents a granular mesh.When the content of NiGNPs is 30%,the agglomeration of GNPs is more serious,resulting in more pores in the cladding layer during the laser cladding process,resulting in a decrease in the compactness of the cladding layer.The introduction of GNPs can refine the crystal grains,and part of the carbides formed by the melting of GNPs increase the hardness of the cladding layer from555Hv0.1 to 745Hv0.1.Secondly,GNPs have good self-lubricating properties due to the weak van der Waals force between the layers,and have anti-friction effect on the friction and wear properties of the cladding layer,which reduces the friction coefficient of the cladding layer from 0.65 to 0.39.Finally,GNPs have good corrosion resistance,which can offset a part of the potential during the electrochemical corrosion process and reduce the potential difference;at the same time,their good impermeability also slows down the corrosion process,making the graphene-enhanced nickel-based composite coating possess Better corrosion resistance.