Studies On Process Paramaters And Microstructure Of Laser Cladding Carbon Nanotube / Fe-based Amorphous Composite Coating

Laser cladding technology is a new type of surface manufacturing technology.It uses laser beam to act on cladding materials and substrate,so as to achieve the purpose of material surface modification,surface repair and direct production of parts.Fe based amorphous alloy coating is a good surface modification material because of its good economy,good strength,strong wear resistance and corrosion resistance.However,the critical cooling rate of Fe based amorphous alloy coating is relatively high,and the preparation process is relatively complex.Coating prepared by laser cladding can meet the requirements of rapid cooling of Fe based amorphous.Because of the brittleness,Fe based amorphous is easy to produce cracks in the process of preparation and use,and the fracture forms show obvious brittle fracture.Therefore,improving the toughness of Fe based amorphous prepared by laser cladding has a strong theoretical significance and application value.In this work,Ni-CNTs/Fe based amorphous composite coating was prepared to improve the toughness of Fe based amorphous coating.The main conclusions are as follows:It is found that the height of the cladding layer is directly proportional to the laser power and inversely proportional to the scanning speed.Low dilution ratio is the necessary condition for the formation of more amorphous layers.The dilution ratio should be controlled within 5%when laser cladding Fe based amorphous layers.The microstructure of the amorphous cladding layer presents gradient distribution,from the matrix to the surface of the cladding layer are epitaxial dendrites,equiaxed dendrites and amorphous.The white particles in the amorphous region of the cladding layer are Nb C contained in the original powder.The eutectic structure of(Fe,Co)₂B and bcc-(Fe,Co)can also be found in the cladding layer,and its morphology presents alveolate aperture.The hardness of the cladding layer presents gradient distribution,corresponding to the structure.The average hardness of the amorphous area is 1615.0HV.The toughness of the cladding layer is poor,and the toughness of the amorphous region is only 5.75 MPa·m^1/2.With the increase of the content of carbon nanotubes,the carbon conversion of the composite powder coating decreased.When the content of Nickel-plated carbon nanotubes increased to 1wt.%,the carbon conversion of the composite powder coating decreased to 72%.When the content of Ni CNTs is 1wt.%,the volume fraction of amorphous phase,quasi nanocrystalline,CNTs and carbide in the cladding layer is 65%,23.8%,5.0%and 6.2%,respectively.The toughness of the composite cladding layer increases with the increase of the content of carbon nanotubes in the cladding layer.The toughness of the composite coating is 7.67 MPa·m^1/2,33.4%higher than that of the amorphous coating.The toughness of the composite cladding layer with carbon nanotubes increased significantly without significant decrease in hardness.The composite mechanical properties of the composite cladding layer with Nickel-plated carbon nanotubes/amorphous were better.