In the aerospace sector, nickel-based superalloys have long been the material of choice for manufacturing critical engine components, thanks to their outstanding high-temperature performance. With the advancement of additive manufacturing technologies, the demand for high-quality nickel-based superalloy powders has grown increasingly urgent. However, conventional powder-production methods either fail to meet quality standards or suffer from low efficiency, posing significant challenges to the industry. Fortunately, a newly developed “Self-Impact Ultrasonic Atomization (SIUA)” process, proposed by a team at Dalian University of Technology, has successfully overcome these limitations, opening up a new avenue for the production of nickel-based superalloy powders.

Challenges in Conventional Powder Preparation

3D printing places extremely stringent demands on metal powders: they must exhibit high sphericity, a uniform microstructure, and an appropriate particle-size distribution—ideally between 15 and 154 μm. These characteristics directly determine the performance of the final printed components. However, the three mainstream fabrication methods currently in use all suffer from significant, hard-to-overcome limitations:

• Gas atomization (GA): This process relies on high-pressure inert gas to break up molten droplets. Although widely used, it entails substantial gas consumption, results in extremely high production costs for high-melting-point alloys, and often yields powders with satellite particles and poor flowability.
• Water Atomization (WA): This method uses a high‑velocity water stream to atomize the material, offering low cost and high throughput. However, the resulting powder particles are irregular in shape and have a high oxygen content, making it unsuitable for highly reactive materials or applications requiring fine powders.
• Plasma Rotating Electrode Process (PREP): This method uses centrifugal force to atomize molten droplets, yielding powders with high sphericity and clean surfaces. However, it is limited to processing conductive rod‑shaped materials, suffers from low material utilization, and requires expensive equipment, making large‑scale production challenging.

More critically, nickel-based superalloys themselves have high melting points, exhibit significant viscosity in the molten state, and possess strong surface tension, making it difficult for conventional methods to simultaneously ensure powder quality and improve processing efficiency. For instance, while ultrasonic atomization (UA) can produce powders with excellent sphericity, its throughput is extremely low when handling such high-viscosity materials, rendering it unable to meet industrial requirements.

Innovative Breakthrough: Self-Impact Ultrasonic Atomization (SIUA)

To address the limitations of conventional methods, a team from Dalian University of Technology focused on the GH4099 nickel-based superalloy and, building on traditional ultrasonic atomization, introduced a “self‑impact” design to develop the SIUA method. The core idea is to control the falling height of molten droplets and leverage the synergistic effects of impact energy and ultrasonic vibration to precisely regulate cavitation during the atomization process, thereby balancing powder quality with processing efficiency.

1. Key Parameter Optimization

The team first conducted repeated experiments on the core parameters that influence atomization performance, ultimately identifying two critical metrics:

• Arc current: If the current is too low, alloy melting will be incomplete, and the molten droplets will exhibit poor wettability with the ultrasonic transducer (made of TZM alloy), preventing the formation of a uniform liquid film. Conversely, excessively high current—such as 200 A—can lead to volatilization of light elements like Al and Ti, resulting in deviations from the intended powder composition. A current of 150 A emerges as the optimal choice, ensuring thorough melting of the droplets while minimizing elemental losses.
• Droplet mass: A single droplet weighing 1.5 g, under a current of 150 A, can rapidly spread into a uniform liquid film and initiate atomization within 20 seconds. However, when the droplet mass exceeds 2 g, gravity counteracts the spreading force generated by ultrasonic vibration, delaying film formation and extending the atomization time to over 30 seconds, thereby significantly reducing efficiency.

2. Drop height

In the SIUA method, the droplet fall height is the “key variable” that determines the atomization performance. The team tested three heights—10 mm (H10), 15 mm (H15), and 20 mm (H20)—and the results were remarkably encouraging:

• H10 (low altitude): The molten droplets exhibit low impact energy, relying primarily on ultrasonic vibration for atomization. Although the powder pass rate for particles in the 15–154 μm range reaches 84%, the atomization time is as long as 24 seconds, resulting in an hourly output of only 189 g and relatively low efficiency.
• H20 (High Altitude): The impact force is excessive, the liquid film is too thin and prone to rupture, cavitation becomes uncontrolled, and the powder pass rate plummets to 43%. Moreover, a large number of irregular, oversized particles are generated, resulting in substandard product quality.
• H15 (Optimal Height): The droplet impact energy is perfectly matched with ultrasonic vibration, resulting in a liquid film thickness that reaches the “critical atomization thickness.” Cavitation effects are precisely controlled, enabling rapid formation of a uniform liquid film while preventing its rupture. Under these conditions, the atomization time is reduced to 19 seconds, with a powder production rate of 210 g/h for particles in the 15–154 μm range and a pass rate of 74%, achieving a dual breakthrough in both efficiency and quality.

SIUA Powder Advantages: Performance comprehensively surpasses traditional PREP.

To verify the quality of SIUA powder, the team conducted a comprehensive comparison with PREP powder, which is widely used in industry. The results showed that SIUA powder outperformed PREP powder in terms of microstructure, sphericity, and compositional uniformity.

1. Higher sphericity: reduces printing defects

According to analysis performed using WinRoof 2018 software, the SIUA powder exhibits an average sphericity of 95.5% with a deviation of only 4.1%; in contrast, the PREP powder achieves a sphericity of 94.9%, but its deviation is as high as 15.9%, and some particles show surface depressions. Higher sphericity indicates improved powder flowability, enabling the formation of a denser powder bed during the powder‑spreading stage of 3D printing and thereby reducing porosity defects in the printed part.

2. More uniform microstructure: enhanced mechanical properties

Under the electron microscope, the microscopic differences between the two powders are immediately apparent:

• PREP powder: Produced by centrifugal atomization, it exhibits a relatively slow cooling rate, resulting in a microstructure dominated by dendrites. Significant elemental segregation occurs between the dendrites, with carbide‑forming elements such as carbon, tungsten, and molybdenum concentrating to form large blocky carbides. These carbides readily serve as stress concentration sites, thereby compromising the high‑temperature strength of the component.
• SIUA powder: The synergistic effect of ultrasonic vibration and impact energy results in a faster cooling rate, yielding a microstructure dominated by cellular grains. Carbides are refined and uniformly dispersed at grain boundaries, while elemental segregation is significantly reduced. This microstructure effectively enhances the powder’s high-temperature creep resistance, making it particularly suitable for fabricating critical components operating under severe high-temperature conditions, such as those found in aircraft engines.

3. No satellite particles: Avoid printing “impurities”

Conventional GA and WA powders often generate “satellite particles” (fine particles adhering to the surface of larger powder particles) due to collisions between molten droplets during atomization. These satellite particles can cause powder agglomeration during printing, degrading part‑forming quality. In contrast, the SIUA method employs a high‑frequency ultrasonic field to rapidly disperse nanoscale molten droplets, preventing their collision with larger droplets. As a result, the resulting powder exhibits a clean surface free of satellite particles, providing higher‑quality feedstock for 3D printing.

Technical significance

The breakthrough of the SIUA method not only resolves the “efficiency–quality” trade-off in the production of nickel-based superalloy powders, but also expands the theoretical boundaries for the application of ultrasonic atomization technology.

SIUA, by introducing a “self‑impact” design, uses impact energy to pre‑spread the molten droplets into a thin liquid film, thereby creating favorable conditions for the formation of capillary waves. At the same time, by precisely controlling the drop‑fall height, it enables fine‑tuned regulation of cavitation intensity, thus overcoming the technical bottleneck that “high‑viscosity materials are difficult to ultrasonic atomize.”

This research not only provides a high-quality powder solution for the 3D printing of GH4099 alloy, but also offers a replicable technical pathway for the powder production of other high-melting-point, high-viscosity alloys, such as titanium alloys and superalloys.

Image and Text Guide

Figure 1. (a) Photograph of the ultrasonic atomization (UA) device; (b) Schematic diagram of the self‑impingement ultrasonic atomization (SIUA) device; (c) Principle of the UA process.

Figure 2. Schematic of the experimental procedure: (a) the SIUA process of droplets; (b) the finite-element model and boundary conditions; (c) sample preparation and surface morphology before and after TEM observation; (d) static droplet contact-angle measurements: (d1) GH4099 high‑temperature alloy specimens of varying masses (1.5 ± 0.05 g, 2.0 ± 0.05 g, 2.5 ± 0.05 g); (d2) morphologies of GH4099 alloy droplets melted on an ultrasonic electrode under different arc currents (100, 150, 200 A); (d3) a contact‑angle goniometer used to measure the contact angles of the GH4099 droplets.

Figure 3. (a) Ex situ droplet‑free morphologies of GH4099 at different arc currents (100 A, 150 A, 200 A) and masses (1.5 g, 2.0 g, 2.5 g), with the corresponding contact angles shown in the upper left corner. (b) Different bottom morphologies of ex situ droplet‑free deposits at 100 A for masses of 2.0 g and 2.5 g. (c) Distinct critical liquid‑film states observed during atomization at 150 A for droplets of different masses (1.5 g and 2.0 g).

Figure 4. Morphology of the liquid film formed when a 1.5 g droplet of GH4099 alloy impacts the electroacoustic electrode at different heights: (a) H10, (b) H15, and (c) H20.

Figure 5. SIUA powder particle size distribution (PSD) after droplets of GH4099 alloy fall from different heights. The curves are fitted using a log-normal distribution.

Figure 6. (a–d) OM and SEM images of the overall morphology of UA GH4099 powder, and (e–h) those of PREP GH4099 powder.

Figure 7. (a, c) SEM images of powder cross-sections prepared by SIUA, and (e, g) by PREP; (b, f) SAED patterns of the interdendritic regions containing carbides; (d, h) EPMA line scans along the dendrites for PREP and SIUA powders, corresponding to the yellow lines in (c) and (g), respectively.

Figure 8. (a) Theoretical model of UA, (b) ideal capillary-wave–induced atomization based on the Faraday instability, (c) unstable capillary waves in an interference system, leading to a distribution of wavelengths and amplitudes, (d) solutions to Mathieu’s equation illustrating the time evolution of the excitation amplitude (τ), and (e) stable and unstable solutions of Mathieu’s equation as functions of α and β.

Figure 9. Simulation results of liquid film diffusion of GH4099 alloy under ultrasonic disturbance at different droplet heights.

Figure 10. (a) Schematic illustration of the atomization behavior of molten self‑impinging droplets at different heights (H10, H15, H20). (b) The three types of powders produced by the SIUA method and (c) cavitation in two distinct forms.

Figure 11. (a) Schematic diagram of the UA process; (b) Schematic diagram of the PREP process, with the microstructure of the melt shown on the left and the powder structure on the right.

From laboratory‑scale parameter optimization to performance that comprehensively surpasses conventional methods, the SIUA technology developed by the team at Dalian University of Technology has demonstrated China’s innovative strength in the field of advanced materials synthesis. Against the backdrop of the aerospace industry’s drive toward “higher temperatures and greater efficiency,” breakthroughs in high‑quality metal powders will provide a more robust material foundation for China’s high‑end equipment manufacturing sector.

In the future, as the SIUA method undergoes further optimization—such as implementing real-time control of droplet quality and falling height via automated equipment, or leveraging numerical simulations to more accurately predict atomization performance—this technology is poised for large-scale industrial deployment. It will enable the “tailor‑made” production of higher‑performance alloy powders for 3D printing, providing fresh momentum to China’s transformation from a “manufacturing giant” into a “manufacturing powerhouse.”