New ultrasonic vibration technology illuminates the future of high-entropy alloy powders—tracing the innovative path to the preparation of TiZrTa0.7NbMo high-entropy alloy powder.

In recent years, driven by the rapid advances in materials science, high-entropy alloys (HEAs) have emerged as a major focus in the next wave of materials research. In particular, refractory high-entropy alloys (RHEAs), with their outstanding high-temperature performance, hold great promise for applications in aerospace, gas turbines, nuclear energy, and other fields.

However, the preparation of high‑quality high‑entropy alloy powders—particularly spherical powders—has long been a major bottleneck limiting their industrial applications. Conventional powder‑making techniques, such as gas atomization and water atomization, while well established, struggle to produce powders of the desired quality when dealing with materials that have high melting points, complex compositions, and high viscosities.

This paper provides a detailed analysis of an innovative powder‑production technique—ultrasonic vibration‑assisted melt atomization—proposed by Professor Dong Fuyu of Shenyang University of Technology and colleagues, focusing on its application in the fabrication of high‑entropy alloy powders. In particular, it presents research findings on the TiZrTa0.7NbMo high‑entropy refractory alloy, offering new avenues for the development of advanced materials with superior high‑temperature performance and mechanical strength.

Background

Traditional powder‑making methods primarily include mechanical grinding, atomization (flame atomization and gas atomization), and electrolytic processes.

1. Basic Concepts of High-Entropy Alloys

Traditional alloys typically use a small number of elements as the primary constituents, with trace elements added to tailor their properties. In contrast, high-entropy alloys depart from this conventional approach by employing a multi‑element composition—often comprising five or more elements in roughly equal proportions—resulting in exceptionally high configurational entropy and endowing them with outstanding mechanical, corrosion‑resistant, and high‑temperature performance.

2. Refractory High-Entropy Alloys (RHEAs)

Due to their excellent high-temperature resistance, oxidation resistance, high hardness, and good toughness, refractory high-entropy alloys have attracted particular attention from industries such as thermal energy and aerospace. High-entropy alloys containing elements like Ti, Zr, Ta, Nb, and Mo exhibit extremely high melting points and outstanding high-temperature performance, making them ideal refractory materials.

3. Challenges in Powder Preparation

Despite the obvious advantages of high-entropy alloys, their powder synthesis remains highly challenging:

• High melting point: Refractory elements have extremely high melting points, making them difficult to melt and atomize rapidly.
• Complex composition: Multi-element systems are prone to segregation and elemental loss.
• Conventional techniques fall short: traditional methods such as gas atomization struggle to produce powders that are spherical, uniformly sized, and free of porosity.

Therefore, developing a novel, efficient preparation technique capable of controlling powder quality has become an urgent priority.

Innovative Breakthrough: Ultrasonic Vibration-Assisted Melt Atomization Technology

1. Introduction to the Technical Principle

Ultrasonic vibration-assisted melt atomization leverages the mechanical vibrations generated by ultrasound to break up molten metal into fine droplets under vibrational action, which are then rapidly cooled and solidified into powder. Compared with conventional gas atomization, it offers the following advantages:

• Controllable particle size: By adjusting the ultrasonic frequency, the particle size can be precisely regulated.
• High powder quality: particles are more spherical in shape, with smooth surfaces and fewer defects.
• Reduce segregation: rapid solidification effectively suppresses elemental segregation.
• Elimination of porosity: The droplets cool rapidly, resulting in fewer pores and impurities.

2. Methodology and Procedure

• Alloy melting: High-purity metallic raw materials are melted in an arc furnace under an inert atmosphere to produce a homogeneous alloy ingot.
• Melted‑metal vibration: Under ultrasonic vibration, the liquid metal is broken into fine droplets.
• Cooling and Solidification: The droplets are rapidly cooled in air or under a protective atmosphere to form a powder.
• Powder Collection: A specialized collection system is employed to produce large quantities of high-quality spherical powder.

This technology is particularly well suited for the preparation of high-entropy alloy powders with high melting points and high viscosities, opening up new possibilities for the industry.

Preparation and Characterization of TiZrTa0.7NbMo High-Entropy Refractory Alloy Powder

01 Experimental Materials and Preparation

The research team selected five high-purity metals—Ti, Zr, Ta, Nb, and Mo—and formulated an alloy with the following molar ratio: Ti:Zr:Ta:Nb:Mo = 1:1:0.7:1:1. The alloy ingots were first produced through repeated melting in a high-vacuum furnace. Subsequently, ultrasonic vibration-assisted melt‑atomization was employed to atomize the liquid alloy into fine powders.

02 Microstructure and Morphological Characteristics of the Powder

Scanning electron microscopy (SEM) observations reveal that the powder exhibits a highly spherical morphology, with a smooth surface free of visible cracks or impurities, and a narrow particle size distribution—meeting the fundamental requirements for high‑quality powders. Furthermore, micro‑computed tomography (Micro‑CT) analysis indicates low internal porosity, with predominantly micropores that are uniformly distributed.

03 Microstructural Analysis of Powders

X-ray diffraction (XRD) analysis indicates that the powder consists predominantly of two body-centered cubic (BCC) phases (BCC1 and BCC2), with no significant interstitial phases or phase transformations observed. This suggests that ultrasonic vibration atomization effectively suppresses segregation, ensuring a uniform elemental distribution.

04 High-Temperature and Hardness Performance

Nanoindentation tests reveal that the powder exhibits a significantly higher hardness—on average approximately 6 GPa—compared to conventional as-cast samples, indicating exceptionally high local strength. This advantage stems from the fine grain structure and microalloying resulting from rapid solidification.

Advantages of Ultrasonic Vibration-Assisted Atomization Technology

1. Achieving High-Quality Powders

Conventional atomization techniques struggle to produce high‑melting‑point, high‑entropy alloy powders that are both pure and spherical with uniform particle sizes. In contrast, ultrasonic vibration‑assisted atomization effectively addresses this challenge, enabling the fabrication of powders with smooth surfaces, minimal contamination, and controllable particle sizes.

2. Enhancing Material Properties

High-quality powders provide a solid foundation for additive manufacturing processes such as laser powder bed fusion (LPBF). Powders prepared using ultrasonic technology significantly enhance forming quality, improving mechanical strength and high-temperature resistance.

3. Reduce preparation costs and energy consumption

Compared with conventional gas atomization, ultrasonic vibration atomization can produce large quantities of high‑quality powders at lower energy consumption, paving the way for industrial-scale production.

Image and Text Guide

Figure 1. Schematic diagram of RHEA powder preparation via ultrasonic atomization.

Figure 2. SEM images of TiZrTa0.7NbMo RHEA powder: (a–c) morphologies of powders screened to particle size ranges of 15–50 μm, 50–100 μm, and 100–150 μm, respectively; (d–f) corresponding particle-size distributions for (a–c).

Figure 3. Micro-CT analysis of TiZrTa0.7NbMo RHEA powder: (a–c) 3D reconstructions of powders in different particle-size ranges; (d–f) 3D representations of pores extracted from (a–c); (g–h) particle-size distribution and sphericity of the powders in (a–c); (j–l) equivalent spherical diameter distributions of pores in (d–f).

Figure 4. Schematic diagram of the ultrasonic atomization mechanism.

Figure 5. XRD pattern of TiZrTa0.7NbMo RHEA powder.

Figure 6. Microstructure and elemental distribution in the cross-section of a single powder particle: (a) BSE image and EDS mapping results; (b) Microstructure and EDS mapping results for the region enclosed by the red box in (a).

Figure 7. EBSD images of a powder cross-section: (a) BC map; (b) IPF map.

Figure 8. Schematic diagram illustrating the mechanism by which ultrasound influences the solidification microstructure of droplets.

Figure 9.0.65: Nanoindentation of the powder cross-section at a loading rate of 5 mN/s and under a load of 10 mN: (a) Load–depth curve; (b) Nanohardness and elastic modulus.

High-entropy alloys, as rising stars in the materials science landscape, hold tremendous promise for a wide range of applications. Yet, producing high‑quality powders remains a critical step in unlocking this potential. Ultrasonic vibration‑assisted melt atomization, with its distinctive advantages, provides a robust platform for the high‑quality fabrication of high‑entropy alloy powders. The successful implementation of this technology not only overcomes the limitations of conventional processes but also ushers in a new era of industrial-scale production for high‑temperature, high‑strength materials. Looking ahead, as the process continues to be refined and equipment is scaled up, ultrasonic vibration technology is poised to play an increasingly pivotal role in the manufacture of advanced materials, driving the next wave of innovation in materials science.