Numerical Simulation Of Atomization Process Of Nickel-based Alloy Powders Prepared By Vacuum Induction Melting Gas Atomization

Vacuum induction melting gas atomization technology(VIGA)is now the most widely used method for preparing metal(alloy)powders in industrial production.The metal powder prepared by VIGA has the advantages of high purity,good sphericity,low oxygen content and rapid solidification.However,it is difficult to characterize the atomization process and reproduce the complex physical process by conventional experimental methods.The method of umerical simulation can realize the visual reproduction of the gas trajectory and the fragmentation of the metal melt.In this paper,ANSYS Fluent 19.0 software and the CFD method is used to numerically simulate atomization process in the production of nickel-based alloy powders by VIGA.The gas flow field in the atomizing chamber and atomization process of the metal melt are studied.The effects of different nozzle structure and atomization process parameters on the atomization process of the metal melt and the particle size distribution of the atomized powders are also studied.The study results shows:(1)Atomizing air flow is sprayed through the nozzle to form supersonic gas flow,whose maximum velocity magnitude is 575 m/s;the recirculation zone is inverted cone.The primary atomization process is completed in the "pulsation atomization" mode,and the melt breakup pattern is an "umbrella shape" or an "inverted fountain shape".The initial droplets undergo secondary atomization in the turbulent layer,and the little broken droplets converge at the stagnation point and rapidly cool and solidify into powder particles.(2)With the increase of the protrusion length of the melt delivery tube,the recirculation zone size gradually decreases,the gas maximum velocity in the recirculation zone gradually decreases,and the suction pressure decreases.The average particle size and D50 of the powder decreased with the decrease of the extension length of the guide tube,and the yield of the fine powder gradually increases,D50 were 90.26,78.04,58.40 μm,respectively.With the increase of the inner-diameter of the melt delivery tube,the content of the metal melt in the ztomizing chamber increased significantly during primary atomization.As the inner-diameter of the melt delivery tube decreased,the average diameter and D50 of the powders gradually decreased,from 93.81μm to 73.32,60.45,58.40 μm,and the particle size distribution range gradually narrowed,the yield of fine powder gradually increased.As the injection angle increased,the gas maximum velocity in the recirculation zone gradually decreased,and the suction pressure decreased.With the decrease of the injection angle,the average particle size and D50 of the powders gradually decreased,and the yield of fine powders gradually increased.D50 were 69.83,68.99,58.40 μm,respectively.(3)With the increase of the atomizing gas pressure,the recirculation zone gradually becomes longer.The maximum value of the air velocity in the recirculation zone increases first and then decreases,the suction pressure increases first and then decreases,and the stagnation pressure gradually increases.With the increase of the atomizing gas pressure,the average diameter of the alloy powder obtained by the numerical simulation statistics of the secondary atomization gradually decreases,D50 gradually decreases,from 81.10 μm to 69.80,64.77,52.30,41.80 μm.And the fine powder yield increases with the increase of the atomizing gas pressure.(4)The flow trajectory of the nickel-based alloy powder prepared by VIGA is basically consistent with the results of simulation experiments.The D50 of gas atomization simulation results and experimental results are 61.89 μm and 69.25μm respectively,and the yield of fine powder(≤53 μm)is 35.48%and 36.82%,respectively,the simulation results are in good agreement with the experimental results.