| Laser cladding is an advanced surface modification technology and an important method for additive manufacturing and parts repair.Using laser cladding to prepare IN718/WC metal matrix ceramic composite coating can greatly enhance the surface wear resistance of the substrate.However,the thermophysical properties of WC Ceramic Particles and IN718 nickel base alloy powder are quite different,and WC particles are easy to deposit at the bottom of the coating,which reduces the microhardness and friction and wear properties of the coating.Aiming at the defects of WC particle deposition and uneven coating properties,the microstructure and properties of the coating were regulated by electromagnetic field assisted laser cladding technology.Through the combination of theoretical analysis and experimental research,the effects of electromagnetic field on WC particle distribution,molten pool convection,heat and mass transfer and microstructure were discussed.On this basis,the improvement mechanism of electromagnetic field on the friction and wear properties of composite coatings at room temperature and high temperature was further discussed.The main contents of this paper are as follows:(1)According to the theories of electromagnetism,laser cladding,metal rapid solidification and dendritic growth,the influence mechanism of electromagnetic field on the convection behavior of liquid metal and the movement of WC particles in the molten pool is analyzed.The generation mechanism of electromagnetic force in the molten pool under the action of electromagnetic field is studied.The influence effect of electromagnetic field on the melt in the solidification process of molten pool is discussed.The principle of refining grain and reducing segregation by electromagnetic field and the influence mechanism of electromagnetic field on the distribution of WC particles in the molten pool are analyzed.(2)The experimental platform of electromagnetic field assisted laser cladding was built.Based on orthogonal experiments,the process parameters of electromagnetic assisted laser cladding were optimized.Taking laser power,scanning speed,powder feeding rate,current and magnetic field intensity as factors,and taking coating melting width,melting depth,melting height and microhardness as evaluation indexes,orthogonal experiments were designed to obtain the optimal combination of process parameters.Based on support vector machine(SVM)theory and particle swarm optimization(PSO),a prediction model between process parameters and melting width,melting depth,melting height and microhardness is established to guide the experiment of electromagnetic assisted laser cladding.(3)The microstructure and phase composition of IN718/WC composite coating before and after electromagnetic field assistance were analyzed,and the distribution law of WC particles in the molten pool was discussed.The variation of microhardness in the depth direction with or without electromagnetic field was studied.The friction coefficient,wear amount and wear trace morphology of the coating before and after electromagnetic field assistance are analyzed,the influence law of electromagnetic field assistance on the friction and wear properties of laser cladding composite coating at room temperature and high temperature is discussed,and the improvement mechanism of microstructure and friction and wear properties of electromagnetic field assisted laser cladding composite coating is revealed. |
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