Study On Heat And Mass Transfer And Microstructure Of Laser Cladding Pool

Laser cladding technology has the characteristics of high flexibility,material saving and short processing cycle,which is widely used in automobile,aerospace and other industries.Its application scenarios are mainly laser cladding coating and laser repair.Laser cladding is a complex physical process with multi-physical fields and multi-factors coupling.How to optimize the microstructure and properties after laser cladding has always been a research hotspot in this field.At present,multi-parameter experimental analysis is widely used but deficient method in the research in this area,which lacks combination of simulation technology.Based on this,this paper takes laser cladding of nickel base superalloy as the research object,and explores the comprehensive influence of process parameters on the shape and microstructure of cladding layer after forming.Also,the mechanism of the influence is analyzed by combining finite element method with experiment.The main research contents are as follows:(1)A three-dimensional transient laser cladding temperature field-flow field coupling model was established based on the finite element theory,and the simulation of temperature field distribution,phase transition interface tracking and uplift caused by powder input to the molten pool surface was realized by using this model.Compared with the traditional temperature field model,the effect of enthalpy release and material flow on the temperature field is considered.(2)On the basis of the above coupling model and combining the concentration field equilibrium equation,the redistribution process of element powder containing Co and Al added to GH4169 substrate was calculated,And analysis shows that the main driving force of solute diffusion in the molten pool is convection.The simulation results were compared with the laser cladding experiment results,and the element distribution percentage deviation was less than 3%,which verified the accuracy of the simulation model.(3)With the method of orthogonal experiment,explored the process parameters of the cladding layer change the influence of the macro geometrical morphology and microstructure morphology,the results show that the width of molten pool and the height of molten cladding both increase with the increase of power and decrease with the increase of scanning speed,the phenomenon is affected by the heat accumulation per unit area,powder input,powder utilization ratio,temperature gradient and other comprehensive factors.(4)The relationship between dendrite growth orientation in different regions of the molten pool and the direction of local maximum gradient was verified by combining the temperature gradient and solidification velocity distribution of solidification line calculated by the simulation model.The primary dendrite spacing under different process parameters was calculated by the KF model,and compared with the measurement results of primary dendrite spacing,the overall deviation was less than 20%,which verified the accuracy of the simulation model.The experimental results show that the scanning speed is the main influence factor of the primary dendrite spacing,and the power has a relatively small effect.