What are the requirements of 3D printing on the performance of metal powder?

3D metal printing powder's requirements

What conditions do metal powders need to meet in order to meet the requirements of 3D printing materials?

1. Purity  

Ceramic inclusions will significantly reduce the performance of the final product, and these inclusions generally have a high melting point and are difficult to be sintered, so no ceramic inclusions must be in the powder. In addition, oxygen and nitrogen content also need to be strictly controlled. At present, powder preparation technology for metal 3D printing is mainly based on atomization. Powder has a large specific surface area and is easy to be oxidized. In special application fields such as aerospace, customers have more stringent requirements on this index, such as oxygen content of superalloy powder is 0.006%-0.018%, titanium alloy powder is 0.007%-0.013%.  The oxygen content of stainless steel powder is 0.010%-0.025%.  

2. Powder particle size distribution  

Different 3D printing equipment and forming process have different requirements for powder particle size distribution. Currently, the commonly used particle size range for metal 3D printing is 15-53μm (fine powder), 53-105μm (coarse powder), and can be extended to 105-150μm (coarse powder) in some cases.  

The selection of metal powder size for 3D printing is mainly divided according to metal printers with different energy sources. Printers with laser as energy source are suitable for using 15-53μm powder as consumables because of its fine focal spot and easy to melt fine powder. Powder replenisher is layer-by - layer powder. The powder-laying printer with 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 53-105μm coarse powder.  For coaxial powder feeder printers, powder with particle size of 105-150μm can be used as consumables.  

3. Powder morphology  

The morphology of powder is closely related to the preparation method of powder. Generally, when metal gas or molten liquid is transformed into powder, the shape of powder particles tends to be spherical, and when metal solid is transformed into powder, the powder particles are mostly irregular shape, and most of the powder prepared by aqueous solution electrolysis is 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.  

4. Powder fluidity and loose density  

The fluidity of powder directly affects the uniformity of powder spreading and the stability of powder feeding.  

The fluidity is related to powder morphology, particle size distribution and bulk density. The larger the powder particles are, the more regular the particle shape is, and the smaller the proportion of very fine powder in particle size composition is, the better the fluidity is.  The fluidity of powder increases with the increase of relative density and particle density.  In addition, the adsorption of water and gas on the particle surface reduces the fluidity of powder.  

Apparent density powder sample is naturally full of container, unit volume of powder quality, in general, the more coarse powder particle size, the larger the apparent density, thickness of collocation powder can obtain higher apparent density, apparent density effects on metal printing density of the final product is uncertain, but apparent density increased, can improve the liquidity of powder.