With the continuous advancement of materials science, the demand for high‑performance alloys with superior corrosion resistance and wear resistance is steadily increasing. Particularly in industries such as aerospace, energy, and electronics, the performance requirements for coating materials are constantly rising. Traditional preparation methods—such as powder metallurgy and mechanical milling—are increasingly unable to meet the needs for precise control and functionalization of complex materials. Against this backdrop, ultrasonic atomization, a green and highly efficient powder‑production technology, has emerged as a key focus in the research and development of advanced materials.

This paper provides an in-depth examination of the principles, characteristics, and advantages of ultrasonic atomization powder‑making technology, as well as its applications in novel materials such as high-entropy alloys (HEAs), with a particular focus on innovative advances in the preparation of high-entropy amorphous alloy powders and coatings.

Ultrasonic atomization powder-making technology

Ultrasonic atomization powder‑making technology leverages the high‑frequency energy of ultrasonic vibrations to transform liquid metals or alloy materials into fine droplets or aerosol‑like particles, which are then subjected to controlled cooling or solidification to produce powders with uniform particle sizes and controllable morphologies.

1. Ultrasonic atomization process:

• Ultrasonic excitation of liquids: Ultrasonic transducers (such as piezoelectric ceramics) generate high-frequency vibrations, transmitting energy to the liquid’s surface.
• Formation of metastable droplets: Vibration generates micron-sized droplets, resulting in a fine, mist-like particle cloud.
• Cooling and Solidification: After exiting the atomization source, the droplets rapidly cool to form a solid powder.

The key to this process lies in the high-frequency vibrations of ultrasound—typically ranging from 20 kHz to 200 kHz—and in the focused transmission of wave energy, which ensures the formation of uniform, finely dispersed droplets.

2. Features and Technical Specifications:

• Controllable particle size: By tuning parameters such as ultrasonic frequency, amplitude, and liquid surface tension, the particle size can be adjusted over a range from tens of nanometers to several micrometers.
• Uniform powder formation: The droplet size is consistent, significantly improving the particle size distribution of the powder.
• High efficiency: rapid preparation, high yield, and suitable for mass production.
• Environmental protection and energy efficiency: No chemical additives are required, reducing pollution and lowering energy consumption.

Advantages of Ultrasonic Atomization for Powder Production

1. Uniform particle size and adjustable dimensions

Ultrasonic milling can produce powders with highly uniform particle sizes, thereby ensuring high‑performance, consistent material properties in subsequent processing and coating fabrication.

2. High purity and pollution-free

No chemical additives are required, minimizing impurity contamination and ensuring high powder purity, which in turn enhances alloy performance.

3. Micron- and Nanoscale Particle Control

It is particularly well suited for the preparation of ultrafine powders, meeting the stringent requirements of advanced materials for precise control of their microstructure.

4. Precision Preparation of Complex Alloys

Multi-element high-entropy alloys exhibit complex multi-component compositions, and ultrasonic atomization enables efficient, uniform mixing of multiple elements, ensuring their even distribution throughout the alloy.

5. Highly adaptable and widely applicable

In addition to metallic materials, it can also be used for powder preparation in a variety of systems, including ceramics and composite materials.

High-entropy alloy

1. Introduction to High-Entropy Alloys

Traditional alloys typically consist of only a few elements, with the elemental composition heavily biased toward one dominant constituent. In contrast, high-entropy alloys break with this convention by incorporating five or more elements in roughly equal or near‑equal proportions, thereby forming a multicomponent alloy system. The high concentrations of these constituent elements give rise to elevated configurational entropy, which stabilizes their distinctive microstructure.

2. Structural Characteristics of High-Entropy Amorphous Alloys

High-entropy amorphous alloys possess an amorphous (disordered) structure, distinct from that of crystalline alloys. This amorphous microstructure endows them with excellent corrosion resistance, wear resistance, and high strength. Moreover, their structure exhibits superior resistance to the propagation of microcracks.

Preparation Process and Structural Characteristics

1. Raw Material Selection and Preparation Methods

This study employed an alloy composition of (ZrTiHfNi)85Nb15 and prepared high-entropy amorphous alloy ribbons via rapid quenching. The specific processing steps include:

• Alloy smelting: Thoroughly mix the elements according to their specified proportions and then melt them.
• Rapid cooling: Employ rapid cooling techniques such as arc thinning or spray forming to ensure the formation of an amorphous structure.
• Powder preparation: Spherical powders with particle sizes ranging from 20 to 80 micrometers were obtained using ultrasonic metal atomization.
• Plasma spraying (APS): Powder is converted into a coating using plasma-spraying technology, with a typical thickness of approximately 200 micrometers.

2. Structural Analysis

• Microstructure: Observed by scanning electron microscopy (SEM), the coating exhibits a composite structure comprising an amorphous phase and a minor nanocrystalline phase.
• Phase composition: X-ray diffraction (XRD) analysis confirms that the coating is predominantly amorphous, with minor FCC and BCC crystalline phases and trace amounts of oxides.
• Elemental distribution: Energy-dispersive spectroscopy indicates that the elements are uniformly distributed throughout the coating, and the particles exhibit good sphericity and a high degree of skeletal structure.

Performance Study

01 Mechanical Properties

• Hardness: The coating’s average hardness reaches 10.5 GPa, significantly exceeding that of conventional alloys and standard coatings, thereby demonstrating excellent wear resistance.
• Elastic modulus: Nanoindentation tests indicate that the coating exhibits a high elastic modulus, effectively mitigating crack propagation.

02 Wear Resistance

• Room-Temperature Wear Resistance: Tested at room temperature, the coating exhibits significant resistance to fatigue‑induced wear, with the primary damage mechanisms being fatigue wear and mild oxidation.
• High-Temperature Wear Resistance: Under high-temperature conditions of 400°C, micro‑deformation increases significantly, and oxidation reactions are intensified, leading to an increase in softening and adhesive wear. At this stage, the fracture and spalling of the oxide film become the dominant failure mechanisms.

03 Corrosion Resistance

• Corrosion testing: In a 3.5 wt.% NaCl solution, electrochemical measurements reveal that the coating’s corrosion current density (I_pass) is significantly lower than that of the substrate and stainless steel, indicating excellent corrosion resistance.
• Mechanistic analysis: Thermodynamic calculations indicate that niobium exhibits low reactivity during the formation of the oxide scale, making it difficult to establish a protective layer in the initial stage; however, in subsequent reactions, it continuously enhances corrosion resistance through secondary oxidation.

Image and Text Guide

Figure 1. Morphology of (ZrTiHfNi)85Nb15 powder (a–b); particle size distribution curve (c); SEM/EDS images showing the cross-section and elemental composition of (ZrTiHfNi)85Nb15 powder (d).

Figure 2. XRD patterns of (ZrTiHfNi)85Nb15 powder, coating, and ribbon (a); DSC curves of (ZrTiHfNi)85Nb15 powder and ribbon (b).

Figure 3. Macroscopic and cross-sectional morphologies of the coating (a, c), surface morphology of the coating (b), and a schematic diagram of porosity statistics (d).

Figure 4. EDS image of the coating cross-section.

Figure 5. Load–displacement nanoindentation curves for the (ZrTiHfNi)85Nb15 ribbon, powder, and coating.

Figure 6. Three-dimensional topography of the coating wear tracks at room temperature (a) and 400°C (b); friction coefficients of the coating at room temperature and 400°C (c); and wear track profile curves (d).

Figure 7. Wear rates of the coating measured at room temperature and at 400°C.

Figure 8. Wear surface morphologies after wear testing at room temperature (a, b) and at 400°C (c, d); the insets on the right show typical EDS analyses of debris.

Figure 9. Illustrative modeling of the tribological process at room temperature (a) and at 400°C (b).

Figure 10. Polarization curves of (ZrTiHfNi)85Nb15 strip, coating, 316L stainless steel, and Q235 steel in a 3.5 wt.% NaCl solution.

Figure 11. Potentiostatic polarization curves (a); equivalent circuit (b); electrochemical impedance spectra, including the Nyquist plot in a 3.5 wt.% NaCl solution (c) and the Bode plot (d).

Figure 12. XPS spectra of the coating’s passive film (a–f) and the strip (h–l) in 3.5 wt.% NaCl.

Figure 13. Histogram of the accumulation of metal cation concentrations in the passivation film.

Figure 14. Schematic illustration of Nb⁵⁺ substitution for Ti⁴⁺ and the continuous cationic diffusion process based on the point-defect model.

High-entropy amorphous alloys, as a novel class of multicomponent materials with high strength and excellent corrosion resistance, demonstrate tremendous application potential. By leveraging advanced ultrasonic atomization powder‑making technology, it is possible to produce powders with uniform microstructures and superior properties, which can then be used to fabricate high‑quality coatings, thereby providing effective technical support for extending the service life of industrial equipment and reducing maintenance costs. Looking ahead, as material design methodologies continue to evolve and ultrasonic atomization processes are further optimized, high-entropy amorphous alloys are expected to find widespread adoption and deployment across an expanding range of applications.

High-entropy alloys represent the future direction of materials science; their unique microstructure and multifunctional properties confer significant advantages in corrosion resistance and wear resistance. With the continuous advancement of ultrasonic atomization powder‑making technology, this emerging class of materials is poised to deliver further breakthroughs and transformations in industrial manufacturing, ushering in a new era of material applications.