Simulation Reasearch On Microstructure Evolution For Laser Additive Manufacturing Of Nickel-base Superalloy

Laser additive manufacturing has unique advantages in the development and production of difficult-to-process materials and complex structure parts,this technology has broad application prospects for small-scale manufacturing of high-value parts.However,the complicated heating and cooling process of laser additive manufacturing makes the control of solidified structure a major challenge.Therefore,in order to control and optimize the additive manufacturing process,it is very important to understand the evolution of the solidification structure.However,due to the short solidification time and the small size of the molten pool,it is difficult to directly observe the evolution process during the experiment.In view of the above problems,this paper selects Inconel 718 alloy as the research object,and uses macro-temperature simulation coupled with micro-phase field simulation tools to study the growth behavior of solidified structure inside the molten pool.First,according to the theory of heat and mass transfer and the theory of system free energy minimization,this paper has carried out a multi-scale model study of the combination of macro temperature field and micro phase field.Aiming at the problem of poor calculation efficiency of the model,optimization work was carried out.Through multi-threaded parallel computing,the running speed of the model is increased by 2.5 times and the memory pressure is reduced by 4 times.Secondly,in this paper,the transverse and longitudinal cross-sectional morphologies of the molten pool are obtained through the laser additive manufacturing experiment,and the temperature distribution cloud map is obtained through the macro temperature field simulation.According to the comparison of the cladding layer morphology of the experiment and the simulation,the validity of the simulation model is verified.Furthermore,using the simulation results of the temperature field,the solidification parameters(temperature gradient G,solidification rate V_s,cooling rate R)of the molten pool solidification interface were obtained,and the influence of the local thermal behavior of the molten pool on the competitive growth of the solidified structure was studied.Through simulation,it is found that the evolution of the solidification structure is affected by the solidification parameters and the position of nucleation.It is found that the solidification parameters affect the elimination rate of grains.The nucleation arrangement affects the generation and elimination of dendrites,which together determine the selection process of grains.At the same time,it also explains the abnormal competition phenomenon found in the simulation process.Finally,this article slices and fits the temperature field data,and inputs it into the microscopic phase field model,breaking through the microscopic limitations of phase field simulation,thus deeply studying the global solidification structure growth behavior of the macroscopic molten pool.Through simulation,it is found that the macroscopic temperature gradient affects the growth behavior of the solidification structure of the molten pool,and determines the grain growth at different positions in the molten pool and the formation of gradually curved grains with the temperature gradient.And matched with the experimental results to verify the reliability and effectiveness of the simulation.