Nowadays, when mentioning 3D printing, it is undoubtedly familiar to everyone. We have previously introduced numerous 3D printing materials and applications. Metal powder is a very important consumable in 3D printing. So, to meet the material requirements for 3D printing, what standards should we refer to when selecting?

Simply put, we should first determine the type of metal powder based on the usage scenario. Then, select the best choice based on the powder's purity, particle size distribution, morphology, and other properties.

What Metal Powders Are Available

Currently, the types of metal powder materials for 3D printing include stainless steel, nickel alloys, titanium alloys, cobalt-chromium alloys, and copper alloys. I have previously written an article introducing the properties and applications of various metal powders, which can be referenced here: Guide to Metal 3D Printing: Choosing the Right Material

Let us briefly summarize the characteristics and main usage scenarios of different metal powders:

1. Titanium alloy powder features excellent strength and toughness, corrosion resistance, low density, and biocompatibility. It is very suitable for many high-performance engineering applications in aerospace and automotive competitions. Of course, producing biomedical implants is also one of its leading fields.

2. Iron-based alloy powder is the most important and widely used metal material in engineering technology. It is mainly used for forming complex structures, such as stainless steel for 3D printing. Compared to traditional casting and forging technologies, it has high strength, excellent high-temperature resistance, wear resistance, and corrosion resistance.

3. Cobalt-Chromium alloy powders are primarily composed of cobalt and chromium, mainly divided into CoCrW and CoCrMo alloys, with good high-temperature mechanical properties and corrosion resistance. Cobalt-chromium alloy parts manufactured by 3D printing not only have high strength but also precise dimensions, making them highly valuable for the personalized customization of dental restorations such as crowns, fixed bridges, and removable dentures.

4. Nickel-based powders possess good high-temperature mechanical properties, oxidation resistance, and corrosion resistance. They are widely used in aerospace, shipbuilding, and petrochemical industries.

5. Copper alloy powders have excellent electrical conductivity, high thermal conductivity, wear resistance, and anti-friction properties. They are mainly used in aerospace, electronics, and mechanical component processing.

Fig 1. Metal Powders for 3D Printing

What Are the Performance Requirements for Metal Powders in 3D Printing

Any powder property that affects the performance of the final product should be considered. Generally, this includes purity, particle size, morphology, flowability, and loose packing density.

1. Purity

Ceramic inclusions can significantly reduce the performance of the final part, and these inclusions generally have high melting points, making them difficult to sinter and form. Therefore, the powder must be free of ceramic inclusions.

In addition, the contents of oxygen and nitrogen also need to be strictly controlled. Currently, the powder preparation techniques used for metal 3D printing are mainly based on atomization. The powders have a large specific surface area and are prone to oxidation. In special application fields such as aerospace, customers have stricter requirements for these indicators. For example, the oxygen content of high-temperature alloy powders is 0.006%-0.018%, titanium alloy powders have an oxygen content of 0.007%-0.013%, and stainless steel powders have an oxygen content of 0.010%-0.025%.

2. Powder Particle Size Distribution

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

The selection of metal powder particle size for 3D printing is mainly based on the classification of metal printers with different energy sources.

• For printers using lasers as the energy source, the focused laser spot is fine, making it easier to melt fine powders, suitable for using powders with a particle size of 15-53 μm as consumables.
• For powder bed fusion printers using electron beams as the energy source, the focused laser spot is slightly coarse, more suitable for melting coarse powders, primarily using coarse powders with a particle size of 53-105 μm.
• For coaxial feeding printers, powders with a particle size of 105-150 μm can be used as consumables.

Fig 2. Powders with different particle size distribution

3. Powder Morphology

Common powder shapes include spherical, nearly spherical (spheroidal), flaky, dendritic, and needle-like. Among them, irregular powders have a larger specific surface area, capable of absorbing more laser energy, which is beneficial for enhancing sintering dynamics. Additionally, pores are conducive to the spreading of the liquid phase. However, isotropic powders, such as those with high sphericity, have better flowability, allowing smooth powder feeding and uniform spreading, which is beneficial for improving the density and uniformity of the formed parts, thereby ensuring the quality of the final product. Therefore, powders used in 3D printing are generally preferred to be spherical or nearly spherical.

Fig 3. Spherical powder and irregular powder

4. Powder Flowability

Powder flowability directly affects the uniformity of powder spreading and the stability of the powder feeding process during printing.

Flowability is related to powder morphology, particle size distribution, and loose packing density. The larger the powder particles, the more regular the particle shape, and the smaller the proportion of ultrafine powders in the particle size composition, the better the flowability. With the same particle density, an increase in relative density improves powder flowability. Additionally, the adsorption of water and gases on the particle surface reduces powder flowability.

5. Loose Packing Density

Loose packing density is the mass of powder per unit volume when the powder sample naturally fills a specified container. Generally, the coarser the powder particle size, the greater the loose packing density. Mixing coarse and fine powders can achieve higher loose packing density. The impact of loose packing density on the density of the final metal printed product is still inconclusive, but increasing loose packing density can improve the flowability of the powder.

Stanford Advanced Materials (SAM) is dedicated to advancing research and innovation in the realm of spherical powder technology. We provide a diverse selection of 3D printing metal powders, including refractory metals, titanium, aluminum, stainless steel, cobalt chromium, nickel, and copper. Our powders are available with high purity levels and precisely controlled particle size distributions to meet the stringent requirements of your applications. If you are interested, please Get A Quote.