Numerical Simulation Of IN718 Alloy Forming Process During Laser Cladding And Investigation On The Micro Structure And Performance

In recent years,with the continuous development of laser cladding,this technology has been gradually applied to various fields such as automotive,energy,electronics,aerospace,medical,etc.,for the manufacture and repair of various components.Nickel-based superalloys have been widely used in aerospace,marine,nuclear,petrochemical and other fields due to their good high temperature mechanical properties,corrosion and oxidation resistance.Laser cladding owns unique advantages in preparing nickel-based superalloys' coating or forming complex parts.However,the laser cladding process is complicated and has many influencing factors.It is extremely challenging to prepare components with good molding quality and mechanical properties.At present,laser cladding nickel-base superalloys still have serious problems of element segregation and poor controllability of solidification structure.It is difficult to observe the solidification process of the alloy by experiment,which seriously restricts the industrial development of the technology.In this paper,laser cladding technology is taken as the research object,and Inconel718 alloy powder is used as the molding material.The above problems are studied by means of simulation and experiment.The aim is to establish a macro-micro coupling model to simulate the solidification process and regulate the solidification structure.The main research contents and results are as follows:(1)In the finite element software ANASYS,the laser cladding temperature field model is established by APDL programming,after that the influence of process parameters on temperature field and process parameters on solidification parameters are analyzed.The results show:the maximum temperature at the edge of the cladding layer is significantly higher than the intermediate position.In actual processing,the defect should be avoided by adjusting the process parameters and the cladding position;the laser power is proportional to the temperature in the molten pool.The scanning speed is reversed,which provides a theoretical basis for process parameter optimization.At the same time,as the laser power increases,the temperature gradient and shape control factor increase,and the cooling rate in the molten pool decreases.The law of scanning speed is opposite to that;along the isotherm from bottom to top,the temperature gradient and shape control factor are reduced,and the cooling rate is increased,which lays a foundation for subsequent regulation of solidification structure.(2)On the basis of the temperature field simulation,the optimal process parameters of laser cladding IN718 alloy are determined by orthogonal experiment:laser power 1200W,scanning speed 8mm/s,powder feeding rate 0.9r/min.The optimized process parameters can be used to prepare a cladding layer with good forming quality and have no obvious defects;white Laves phase forms in interdendritic produced by Nb segregation,and the morphology of Laves phase shows a strong dependence on the dendrites' morphology.(3)A macro-micro coupling model(CA-FE)is programmed in Matlab,through it,a series of dynamic IN718 alloy molten pool solidification processes,including nucleation,dendrites growth,solute redistribution and Laves phase formation is calculated.Afterwards,the calculation results are verified by experiments.(4)The cooling rate of the molten pool can be increased by changing parameter.After that,the grain can be refined,Laves phase concentration reduces and its morphology change,the long chain Laves phase disappears.The concentration of Laves phase in the cladding layer prepared under forced cooling of liquid nitrogen is the lowest.Due to the temperature of ice water is much higher than liquid nitrogen,the optimization result is not good,but the concentration of Laves phase is lower that air cooling.(5)A small amount of vanadium powder(0.066 wt.%)is mixed into the IN718 alloy powder to prepare V-containing cladding layer,and the microstructure is compared with of the blank cladding layer.The results indicate The porosity,average dendrite size,secondary dendrite arm of the V-containing cladding layer decrease,the Laves phase content decreased by 80%,and its morphology become granular.In addition,the average Vickers hardness of the V-containing cladding layer increased from 228HV to 261HV.