Introduction

Spherical powder is the cornerstone of additive manufacturing, commonly known as 3D printing, playing a pivotal role in determining the quality and precision of the final products. Its importance stems from its unique properties, such as excellent flowability and uniform packing density, which are essential for producing high-quality prints with intricate details and minimal defects.

The development of 3D printing technology, especially in the metal sector, has made spherical powder even more critical. As metal 3D printing continues to advance rapidly, driven by innovations in aerospace, automotive, and medical industries, the demand for spherical metal powder is expected to soar. This growth is not just a trend but a reflection of the powder's indispensable role in pushing the boundaries of what 3D printing can achieve, making it a key focus area for research and industrial investment.

What Are Spherical Powder

Spherical powders refer to materials composed of tiny particles that are nearly spherical. Compared to powders with irregular shapes, spherical powders have more symmetrical and regular particle shapes. This geometric form provides spherical powders with unique advantages in industrial and manufacturing processes. Spherical powders are widely used in additive manufacturing (3D printing), powder metallurgy, metal injection molding (MIM), and thermal spraying.

Fig 1. C103 Spherical Powder

--Advantages of Using Spherical Powders

Spherical powder is the most ideal material shape for 3D printing because it offers many advantages.

• Excellent Flowability: The symmetry and smooth surface of spherical particles give the powder better flowability, which is crucial for mold filling, 3D printing, and injection molding.
• High Packing Density: Spherical powders can pack more tightly, increasing the material's packing density. This directly impacts the density and mechanical properties of the final product.
• Good Uniformity: The shape and size of spherical powder particles are easy to control, which results in better uniformity during processing and reduces the occurrence of defects.
• Reduced Friction and Wear: Due to their smooth surface, spherical powders reduce friction and wear within equipment, extending the equipment's service life.
• Reduced Oxidation and Contamination: Spherical powders are typically formed in an inert gas or vacuum environment during production, reducing the risk of oxidation and contamination, thereby increasing the powder's purity.
• Enhanced Sintering Performance: High sphericity and tight packing help form dense materials during sintering, improving the final product's strength and durability.
• Wide Adaptability: Spherical powders are suitable for a variety of processing techniques, including laser melting, plasma spraying, and others, allowing them to perform well across different manufacturing processes.

Fig 2. Spherical powders and irregular powders

--Applications of Spherical Powders

Additive manufacturing is the most widely used field of spherical powder. Apart from this, spherical powder is also used in various other industries due to its unique advantages.

• Additive Manufacturing (3D Printing): Spherical powders are widely used in 3D printing, especially in metal additive manufacturing, where the flowability and packing density of the powder directly affect the stability of the printing process and the quality of the final product.
• Powder Metallurgy: In powder metallurgy, spherical powders help improve the density and strength of sintered bodies, reduce porosity, and enhance the mechanical properties of materials.
• Metal Injection Molding (MIM): The uniform particle size and high flowability of spherical powders make it easier to fill molds during injection molding, reducing the formation of defects.
• Thermal Spraying: Spherical powders can form uniform, dense coatings during thermal spraying, which are widely used in surface engineering.

Spherical powders are also suitable for various processing techniques, including laser melting, plasma spraying, etc., allowing them to perform exceptionally well across different manufacturing processes.

Key Parameters Affecting Powder Performance

The table below shows the main parameters that have a significant influence on the powder properties.

Table 1. Key Parameters of Metal Powders

How to Get Better-performance of Spherical Powder

Powder preparation process is very important for determining the shape, particle size, and purity of spherical powders. We need to identify the major methods of powder preparation and a series of challenges faced during the process.

--The Preparation of Spherical Powders

In order to meet the requirements of 3D printing equipment and processes, metal powders must have low oxygen and nitrogen content, good sphericity, narrow particle size distribution range, and high bulk density. Therefore, it is particularly important to study the preparation of metal spherical powders.

1. Gas Atomization (GA)

Gas atomization utilizes inert gas at high speeds to atomize liquid metal, which then condenses into spherical powder. Depending on the heat source, gas atomization can be further divided into Electrode Induction Melting Gas Atomization (EIGA) and Plasma Inert Gas Atomization (PIGA).

The use of inert gas prevents product oxidation and avoids environmental contamination. In the EIGA process, pre-alloyed rods in electrode form are induction melted and atomized without the use of a melting crucible.

The resulting powders typically have a wide particle size distribution, with most particles being fine. However, due to different cooling rates based on particle size, hollow structures may form, leading to uneven powder shapes and potential negative impacts on subsequent applications.

Fig 3. Principle of Gas Atomization (GA)

2. Plasma Rotating Electrode Process (PREP)

PREP is a centrifugal atomization technique commonly used to produce high-purity spherical titanium powder. The basic principle involves melting the end face of a consumable electrode with a plasma arc, creating a liquid film that is rapidly ejected under centrifugal force to form droplets. These droplets then spheroidize under surface tension and solidify into spherical powder.

PREP offers high purity due to the use of a consumable electrode and avoids the formation of hollow or satellite particles. However, the particle size distribution is relatively narrow (mainly between 50-150μm), and the yield of fine powder is low.

Fig 4. Principle of Plasma Rotating Electrode Process

3. Plasma Wire Atomization (PA)

In plasma wire atomization, high-purity metal or alloy wire is used as raw material, and a plasma gun serves as the heat source. The wire is instantly melted by the plasma and simultaneously atomized by the high-temperature gas, forming small droplets that spheroidize under surface tension and cool into spherical particles.

The PA process offers high traceability and good control over particle size. The resulting powder typically has a narrow particle size distribution (average around 40μm), high fine powder yield (80%), and minimal satellite particles. It also boasts high purity (low oxygen, no inclusions), high sphericity, excellent flowability, apparent density, and tap density.

Fig 5. Principle of Plasma Wire Atomization

4. Radio Frequency Plasma Spheroidization

Radiofrequency plasma spheroidization uses RF electromagnetic fields to induce heating in various gases (mostly inert), creating a plasma that melts non-spherical powders. These powders then pass through a steep temperature gradient, quickly condensing into small spherical droplets, forming a spherical powder.

Research shows that this process can achieve a powder size range of 20-50μm, with a fine powder yield exceeding 80%.

Fig 6. Principle of Radio Frequency Plasma Spheroidization

--Challenges and Solutions During Spherical Powder Preparation

Gas atomization is the most commonly used method for producing spherical metal powders, but it faces several challenges in the production of spherical powders.

1. Particle Size Distribution Control

• Challenge: Accurately controlling the particle size distribution during gas atomization is a significant challenge. A broad particle size distribution can lead to inconsistent performance in subsequent processing.
• Solution: Optimizing nozzle design, adjusting gas flow rate, and controlling melt temperature can better manage particle size distribution. Additionally, using multi-stage gas injection and cooling systems can aid in achieving precise particle size control. In post-processing, sieving equipment can be used to sort the powder into the desired size range.

2. Oxidation Issues

• Challenge: Molten metal at high temperatures can easily react with oxygen in the air during atomization, forming oxides on the powder surface and affecting its purity and processing performance.
• Solution: Protective atomization using inert gases such as argon or nitrogen can reduce oxidation. Optimizing equipment sealing to minimize the exposure of molten metal to air is also crucial. For highly reactive metals like titanium, atomization in a vacuum environment may be considered.

3. Cooling Rate Control:

• Challenge: The cooling rate significantly affects the particle morphology and internal structure. Too fast or too slow cooling rates can lead to irregular particle shapes or internal stress cracks.
• Solution: Precisely controlling the gas flow speed and cooling medium temperature can help regulate the cooling rate. Multi-stage cooling systems can gradually reduce the temperature, preventing defects caused by rapid cooling.

4. High Energy Consumption and Equipment Costs:

• Challenge: Gas atomization is energy-intensive, especially when processing high-melting-point metals, leading to high production and maintenance costs.
• Solution: Optimizing process parameters, such as reducing gas pressure and melt temperature, can lower energy consumption. Improving equipment design to enhance energy efficiency, such as implementing heat recovery systems to recycle waste heat, can also reduce overall energy costs. Additionally, researching and developing new low-energy atomization technologies is an effective way to cut costs.

Choose A Trusted Spherical Powder Supplier

Stanford Advanced Materials is a trusted supplier of spherical powders. We offer high-purity spherical powders of different types and sizes for customers to choose from. Our products adhere to strict quality standards throughout the manufacturing process. Table 2 is our best-selling metal spherical powder.

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Conclusion

In summary, spherical powders offer significant advantages for 3D printing, including superior flowability, high packing density, and enhanced uniformity, making them ideal for precise and reliable manufacturing. However, the preparation of these powders presents challenges such as particle size control, oxidation, and energy efficiency. Addressing these challenges is key to optimizing powder quality, ultimately driving the advancement of 3D printing technologies and expanding their industrial applications.

Related articles:

Plasma Rotating Electrode Process (PREP) and Plasma Atomization (PA): How to Choose

Gas-Atomized Spherical Powders for Additive Manufacturing

Reference:

[1]. Yin, Zhengxin & Yu, Deping & Zhang, Qingbo & Yang, Shengyuan & Yang, Tong. (2021). Experimental and Numerical Analysis of a Reverse-polarity Plasma Torch for Plasma Atomization. Plasma Chemistry and Plasma Processing. 41. 10.1007/s11090-021-10181-8.

[2]. Krishna, Ram & Mohan, Sreenivasan & Lyutyk, Mykola & Barosh, Mykola. (2021). Characterization of Spheroidized Alumina Powders for Ceramic 3D Printing Application. 10.1007/978-3-030-71956-2_20.