Atomization Behavior And Mechanism Of Alloy Powders Prepared By Plasma Rotating Electrode Method

Plasma Rotating Electrode Process(PREP)powders is characterized by high sphericity,good flowability,and small powders oxygen increase,and is widely used in the field of additive manufacturing.At present,research on PREP powders production mainly focuses on the impact of process parameters on powders particle size and its distribution,but there is still a lack of systematic study on the atomization mechanism of PREP powders and the formation mechanism of particle defects,which limits the further improvement of PREP powders performance.This study takes Ti-6Al-4V,Co-Cr-Mo,and 316 stainless steel alloy powders prepared by the PREP method as research subjects,and uses laser particle size analyzers,scanning electron microscopes,electron backscatter diffraction instruments,and computed tomography scanners to characterize the distribution of powders particle size,powders morphology,flowability,porosity,and residual rod head morphology at different rotation speeds;it discusses in detail the PREP atomization mechanism and the formation mechanisms of satellite powders,irregular powders,and hollow powders,providing important reference value for optimizing PREP process parameters and improving powders performance.(1)Comparative studies on the particle morphology,particle size distribution,flowability,and bulk density of Ti-6Al-4V,Co-Cr-Mo,and316 stainless steel powders under different rotation speeds(8000-14000rpm)of the PREP electrode rod were conducted.Based on this,the evolution behavior of the powder atomization mechanism with the change of rotation speed was deeply analyzed,and the relationship between the atomization behavior and powder particle size and its distribution was summarized.The particle size of the three kinds of alloy powders prepared by the PREP method under different rotation speeds showed a typical single-peak distribution,and with the increase of rotation speed,the average particle size of the powders decreased,the proportion of fine powders increased,the flowability worsened,and the relative bulk density increased.Within the range of 8000-14000 rpm,all three powderss are mainly atomized by the Ligament Disintegrating(LD)mechanism.As the rotation speed increases,the leading role of the LD mechanism in the atomization process gradually strengthens,resulting in finer powders particles.(2)The formation behavior and mechanism of satellite and irregular powders in three alloy rods during the PREP powders production process at different rotation speeds were studied.The proportion of satellite powders and irregular powders is closely related to PREP rotation speed,material density and surface tension,and the thermal conductivity of the alloy.The proportion of irregular powders and satellite powders both decrease with the increase of rotation speed or the decrease of average powder particle size;satellite powders has three morphologies,all of which are influenced by the airflow in the atomization chamber and are formed by the fusion of atomized droplets after collision.Irregular powders mainly form at the edge of the electrode rod and are influenced by the molten pool movement state of the electrode rod.They are produced when the liquid film on the surface of the rod is peeled off from the end face of the electrode rod under the combined action of centrifugal force and airflow shear force.(3)The morphology,content evolution behavior,and formation mechanism of hollow powders at different rotation speeds of the PREP electrode rod were studied.It was found that powder particle size,rotation speed,and material droplet surface tension have a significant impact on the formation of pores.At a given rotation speed,coarse powders(>250 μm)has a higher proportion of hollow powders.As the rotation speed increases,the proportion of hollow powders in the original atomized powders gradually decreases.Compared to the other two alloys,Ti-6-Al-4V alloy has a significantly higher proportion of hollow powders at low rotation speeds,but no significant difference at high rotation speeds.Hollow powders are formed when metal droplets are not completely solidified and are torn by strong airflow and entrapped.(4)A comparative analysis of the performance of Ti-6Al-4V,Co-CrMo,and 316 stainless steel alloy PREP powders with commercial Gas Atomization(GA)powders and Electron Beam Melting(EBM)additive manufacturing materials was conducted.Compared to commercial GA powders,PREP powders have better flowability and lower hollow powders content.As a result,PREP powders have a more even spread,less inherited defects from hollow powders,fewer defects in additive manufacturing materials,a longer fatigue life,and better plasticity,which shows the great potential application prospects of PREP powders in the field of additive manufacturing.