Metal powder for 3D printing

Main performance indicators of 3d metal printing powder

Purity: Because the ceramic inclusions will significantly reduce the performance of the final product, and these inclusions generally have a high melting point, which is difficult to be sintered, so it is required that the powder contains no ceramic inclusions.  In addition, oxygen and nitrogen content also need to be strictly controlled.  In aerospace and other special application fields, the purity requirements are more strict, such as the oxygen content of superalloy powder is 0.006% ~ 0.018%, titanium alloy powder is 0.007% ~ 0.013%, stainless steel powder oxygen content is 0.010% ~ 0.025% (all are mass fraction).

Powder particle size distribution: the selection of 3D printing metal powder particle size is mainly based on different energy sources of metal printers, laser as the energy source of the printer, because of its fine focal spot, easy to melt fine powder, suitable for the use of 15 ~ 53μm powder as consumables, powder supply method is layer by layer powder;  The powder-laying printer, which uses electron beam as energy source, has a slightly coarse focal spot, which is more suitable for melting coarse powder. It is mainly suitable for using coarse powder of 53 ~ 105μm.  For coaxial powder feeding printer, powder with particle size of 105 ~ 150μm can be used as consumables.

Powder morphology: powder morphology and powder preparation method is closely related, generally from metal gas or molten liquid into powder, powder particle shape tends to be spherical;  From solid to powder, powder particles are irregular shape;  Most powders prepared by aqueous solution electrolysis are dendritic.  In general, the higher the sphericity, the better the fluidity of powder particles.  The sphericity of metal powder for 3D printing is required to be above 98%, so that it is easier to lay and feed powder during printing.  The following table shows the morphology of metal powders corresponding to different powder preparation methods.  

Powder fluidity and loose density: powder fluidity directly affects the uniformity of powder laying and the stability of powder feeding process in the printing process.  The fluidity is related to powder morphology, particle size distribution and bulk density.  The larger the particle size, the more regular the particle shape, the smaller the proportion of the very fine powder in the particle size composition, the better its fluidity.  The fluidity of powder increases with the increase of relative density and particle density.  Adsorption of water and gas on particle surface reduces powder fluidity.  Bulk density is the powder mass per unit volume of a powder sample when it naturally fills a specified container.  In general, the coarser the powder particle size, the greater the bulk density, the powder can get a higher bulk density.  The effect of loose packing density on the density of metal printed final product is not determined, but the fluidity of powder can be improved with the increase of loose packing density.

Classification and preparation method of 3d metal printing powder

At present, 3D printed metal powders widely used include titanium alloy, aluminum alloy, stainless steel, superalloy, copper alloy, refractory metal and other metals such as high entropy alloy, amorphous alloy, etc.

Metal powder preparation methods for 3D printing mainly include electrode induction atomization (EIGA), plasma rotating electrode atomization (PREP), plasma spheroidization (PA), vacuum induction melting gas atomization (VIGA) and water atomization, etc. In comparison, EIGA, PREP and PA methods are more widely used in powder preparation.