Study On The Effect Of Powder Characteristics On The Building Quality Of GH3230 Alloy On Laser Powder Bed Fusion

In laser powder bed fusion process,the building of high alloying and high performance alloys generally faces the problems of difficult to control defects,narrow process window,large fluctuations in performance,high production costs,etc.This paper takes GH3230 high temperature alloy,which is widely used in aerospace field,as an object,and focuses on the study of the effects and mechanisms of powder particle size and morphology,surface energy,and surface roughness on the powder flow and spreading behavior,powder spreading quality,and building defects,and establishes the relationship between powder particle characteristics,spreading coefficient,powder bed density,and building densities and building defects,established the relationship between powder particle characteristics,spreading coefficient,powder bed density and building density,and combined with the optimization of powder C elements to obtain high density crack-free GH3230 alloy.The main research results are summarized as follows:Variations in powder particle characteristics affect the powder flowability and spreadability,which in turn affects the powder spreading density on the powder bed and ultimately the building densities.Compared to the gas atomization processes,VIGA and EIGA,the powders prepared by the PREP process contributed to the excellent flowability and spreadability of the powders due to the narrow particle size distribution,high sphericity of the powders,and minimal surface roughness of the particles,which in turn resulted in the highest powder bed densities and building densities.The decrease in the surface energy of the powder enhanced the flowability and spreadability of the powder,which in turn enhanced the powder bed density and building densities.The increase in particle surface roughness reduces the flowability and spreadability of the powder,which in turn reduces the powder bed density and building relative density.The nature of the effect of changes in powder particle characteristics on flowability and spreadability is to alter the competitive relationship between cohesion and gravity between particles.Compared with the two gas atomization processes of VIGA and EIGA,the powder prepared by the PREP process has a narrow particle size distribution,high powder sphericity,and minimum particle surface roughness,which contributes to the excellent flow and spreadability of the powder,thereby obtaining the highest powder quality.Bed density and building density.The reduction in powder surface energy improves the flowability and spreadability of the powder,thereby increasing the powder bed density and building density.The increase in particle surface roughness reduces the flowability and spreadability of the powder,thereby reducing the powder bed density and building density.Based on Rumpf’s particle contact theory,a mathematical model was established for the influence of three powder particle characteristics on the Bog coefficient,namely,average particle size,particle surface energy and surface roughness.The influence of the average particle size of the powder on the Bog coefficient is nonlinear,when the average particle size is less than 20μm,the reduction of the particle size will cause a significant increase in the Bog coefficient,when the average particle size between 20-40 μm,the Bog coefficient of the average particle size is sensitive to the change of the Bog coefficient,and when the average particle size is more than 40μm,the gravity of the powder is gradually dominant,and the powder shows a free-flow characteristics.The surface energy of the powder and the Bog coefficient are positively proportional,and the size of the proportionality coefficient is determined by the average particle size and the particle surface roughness of the powder.The effect of the surface roughness on the Bog coefficient of the powder shows a tendency of decreasing and then increasing.Through the above results,simultaneously increasing the average particle size of the powder,reducing the particle surface energy,and reducing the particle surface roughness within an appropriate range is the most effective method to obtain powder with excellent flowability and spreadability and improve building density.On the one hand,the building cracks of GH3230 alloy are influenced by the powder particle characteristics.On the other hand,the adjustment of the C content in the powder composition plays a dominant role in eliminating the cracks.Firstly,by optimizing the average particle size,particle surface energy and surface roughness of the powder,and reducing the Bog coefficient to less than 5.5,the powder will obtain excellent spreadability and higher powder bed packing density,which ultimately improves the pore defects and cracks in the building samples,and the building densities will be increased to more than 99.40%.Secondly,by increasing the C content to more than 0.28%,the building cracks are completely suppressed.The building relative densities are further increased to more than 99.94%.Finally,through the optimization of powder particle characteristics and the adjustment of powder C content,the higher relative density and crack-free GH3230 alloy were obtained,which provide powder support for future high-alloying and high-performance alloy building.