I. Research Background: Why Are Platinum-Based Superalloys Receiving So Much Attention?

Nickel-based superalloys have long dominated high-temperature industrial applications, delivering excellent performance through the Ni₃Al strengthening phase; however, their service temperature is significantly limited. In contrast, platinum-based superalloys can operate stably at temperatures up to 200°C higher than those of nickel-based alloys, exhibiting markedly superior overall performance.

The one selected for this study is Pt84-Al11-Cr3-Ru2 (atomic percentages) Alloys are the preferred systems that have undergone multiple rounds of compositional optimization:

• Aluminum: Forms an alumina protective oxide layer on the alloy surface, enhancing oxidation resistance, while also generating the Pt₃Al intermetallic compound to achieve precipitation strengthening.
• Chromium: Stabilizes the L1₂ cubic structure of Pt₃Al, simultaneously providing both precipitation strengthening and solid-solution strengthening, thereby optimizing the alloy’s mechanical properties.
• Ruthenium: Further enhances the alloy’s microstructure and high-temperature stability.

Constrained by the high cost of platinum and the significant forming challenges inherent in conventional casting processes, Powder Metallurgy + Metal Additive Manufacturing This has become the mainstream approach for the practical application of such alloys. Additive manufacturing incurs far lower material waste than conventional subtractive processes, making it particularly well-suited to the processing needs of high‑cost platinum‑group metals and offering broad market potential. Industry forecasts project that by 2028, the global market for precious metals used in additive manufacturing will approach US$2 billion, with the value of platinum applications continuing to rise.

Previous studies have attempted to prepare this alloy powder using techniques such as water atomization and mechanical alloying, but all were unsuccessful due to the facile oxidation of aluminum. To address this issue, the present study introduces… Ultrasonic atomization technology , exploring preparation routes for high-quality platinum-based alloy powders.

II. Core Process: A Detailed Analysis of Ultrasonic Atomization Powder-Production Technology

Ultrasonic atomization powder production It is the core process of this experiment. Unlike conventional powder‑making methods, this technology relies on high‑intensity ultrasonic vibration to produce metal powders, meeting the stringent requirements of additive manufacturing for spherical particles.

1. Process Principle

Using a plasma arc (TIG torch with an arc‑extending tip), the blended alloy feedstock is melted into liquid metal, and then, with the aid of… High-frequency ultrasonic vibration The molten metal is atomized into tiny droplets; these droplets are rapidly cooled and solidified in an inert atmosphere, ultimately yielding spherical metal powders. The ultrasonic frequency directly determines the powder particle size: higher frequencies produce finer particles.

2. Experimental Parameters and Procedure

Due to constraints on the cost of platinum materials, this experiment utilized only 10g A single‑element mixed powder (Pt, Al, Cr, Ru) was subjected to a single experiment, with the complete procedure as follows:

• Powder blending and compaction: The elemental powders are blended according to the target composition for 30 minutes, then compacted into a green body using a 70 kN load.
• Atmosphere protection: The equipment chamber is subjected to multiple vacuum cycles and purged with argon, with all operations conducted under an inert atmosphere to prevent aluminum oxidation; meanwhile, titanium components are preheated to desorb residual oxygen.
• Ultrasonic Atomization: Utilizing the AMAZEMET rePowder ultrasonic atomization system, Ultrasonic frequency: 40 kHz , ultrasonic amplitude of 150%, and an arc welding current of 300 A; the 40 kHz operating parameters ensure a narrow particle size distribution, yielding powder that is well-suited for laser powder bed fusion (L-PBF) additive manufacturing.

III. Experimental Results: Characterization of Powder Morphology, Composition, and Particle Size

The study characterized the powder from three key aspects—morphology, chemical composition, and particle size distribution—using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and laser particle sizing.

1. Powder morphology

As shown in Figure 1, the powder prepared by ultrasonic atomization It is generally spherical in shape. , the satellite particles are few in number, fully meeting the fundamental requirements for powder morphology in 3D printing processes such as laser powder bed fusion.

2. Chemical Composition Analysis

Alloy composition was determined by particle‑cross‑section scanning and single‑point line scanning, and the results were compared with the target composition, as shown in the table below:

Table

Data show that the measured composition is largely consistent with the target composition, but… Significant aluminum loss was observed. Based on the material‑specific analysis, aluminum has a low melting point and high volatility, making it prone to evaporation under the high‑temperature conditions of atomization—this is the primary cause of compositional deviations. Meanwhile, elemental mapping confirms that Al, Cr, and Ru are uniformly distributed within the platinum matrix, indicating effective alloying. However, due to the rapid cooling during atomization, the Pt₃Al strengthening phase did not fully precipitate, and the particles exhibit microsegregation resulting from dendritic solidification, along with a small number of microscopic pores.

3. Particle Size Distribution

The powder appears Bimodal particle size distribution , The particle size data are summarized as follows:

• Dv(10): 23.0 μm
• Dv(50): 54.2 μm
• Dv(90): 475 μm

The median particle size D50 is 54.2 μm, meeting the specifications for laser powder bed fusion processes. The presence of large particles in the system is primarily attributable to two issues: droplet splashing during melting and fragmentation of incompletely melted solid feedstock. Due to limitations in the amount of experimental samples, process optimization has not been pursued at this time.

IV. Research Conclusions and Future Prospects

1. Core Conclusion

• Adopt Plasma melting + ultrasonic atomization By employing a combined processing approach, spherical Pt84‑Al11‑Cr3‑Ru2 platinum-based high-temperature alloy powder was successfully prepared; the powder morphology and matrix alloying effects meet the fundamental requirements for additive manufacturing.
• During the atomization process, aluminum loss due to volatilization is the primary challenge in compositional control.
• The powder exhibits a bimodal particle-size distribution: the predominant spherical particles are well-suited to the L-PBF process, but liquid spatter and feedstock fragmentation generate a significant fraction of large particles, necessitating further process optimization.

2. Optimization Recommendations and Application Directions

• Process Optimization: Comparison of Different Options Ultrasound frequency , meeting the powder requirements of various additive manufacturing processes such as powder bed fusion and metal binder jetting; adjusting the aluminum content of the raw material and the atomization temperature to compensate for aluminum volatilization losses; optimizing atomization parameters to minimize the formation of oversized particles;
• Application Implementation: Following process optimization and the successful large-scale production of the powder, this material can be used for 3D printing ultra‑high‑temperature industrial components, thereby advancing the practical application of platinum‑based superalloys in areas such as gas turbines, glass manufacturing, and high‑end thermocouples.

Image and Text Guide

Figure 1. Scanning electron microscope secondary electron images of Pt–Al–Cr–Ru alloy powder after ultrasonic atomization: (a) low-magnification view; (b) high-magnification view.

Figure 2. (a) Several powder particles and (b) elemental X-ray distribution maps of the cross-sections within a single powder particle.

Figure 3. Line-scan images of 26 points within the powder particles, showing the elemental distribution (in weight percent) of aluminum (Al), chromium (Cr), and ruthenium (Ru).

Figure 4. SEM secondary electron image of the powdered sample area.

Table I. Chemical composition of the target alloy determined by SEM‑EDS (expressed in atomic percent and mass percent, with ± standard deviation), based on line-scan and area-scan averages for platinum‑based superalloys.

Figure 5. Powder Particle size distribution

Figure 6. Secondary electron images obtained by scanning electron microscopy (SEM) reveal both the larger particles and the smaller particles that give rise to the second peak in the bimodal size distribution.

Table II. Summary of PSD Results for Ultrasonic Atomization of Platinum-Based Alloys