Key Takeaways & Executive Findings
- •• • Optimal hydrogenation at 550 °C, 0.25 MPa H2 for 2 h yields hydride powder with D50 = 11.13 μm, H = 1.823%, O = 0.111%, enabling efficient mechanical crushing due to hydrogen embrittlement. • • Vacuum dehydrogenation at 450 °C for 1.5 h reduces hydrogen to 0.028% while limiting oxygen increase to 0.121%, achieving single-phase BCC structure essential for mechanical properties. • • The HDH process reduces average particle size from 11.13 μm to 5.67 μm, narrowing size distribution, which enhances sintering activity and densification in powder metallurgy. • • The process achieves low oxygen contamination (0.121%) compared to mechanical alloying or gas atomization, critical for preserving ductility and energy release performance in structural applications.
Abstract
TiZrNbTa refractory high-entropy alloy (RHEA) is an active alloy with excellent mechanical properties and energy release characteristics. However, its high and disparate melting points of constituent elements and wide liquid-solid two-phase region hinder large-scale forming via conventional casting. Powder metallurgy offers a viable route, but obtaining suitable powder is critical. This study systematically investigated the hydrogenation-dehydrogenation (HDH) process for preparing equimolar TiZrNbTa RHEA powder. The as-cast alloy was hydrogenated at 550 °C under 0.25 MPa hydrogen pressure for 2 h, transforming the BCC solid solution into metal hydrides (ZrH2, TiH2, and (Nb,Ta)H). Mechanical crushing yielded irregular hydride powder with an average particle size (D50) of 11.13 μm, and hydrogen and oxygen contents of 1.823% and 0.111%, respectively. Subsequent vacuum dehydrogenation at 450 °C for 1.5 h produced single-phase BCC TiZrNbTa powder with significantly reduced hydrogen (0.028%) and slightly increased oxygen (0.121%) contents, and a narrower particle size distribution with D50 reduced to 5.67 μm. The results demonstrate that the HDH process is an effective method for producing low-oxygen TiZrNbTa RHEA powder with suitable particle size for powder metallurgy applications.
1. Introduction
TiZrNbTa refractory high-entropy alloys (RHEAs) exhibit a unique combination of high mechanical strength and exothermic energy release, making them promising for energetic structural materials in penetrator warheads. However, their high melting points and wide solidification range cause casting defects, limiting large-scale production. Powder metallurgy offers an alternative, but conventional powder fabrication methods such as mechanical alloying or gas atomization suffer from high oxygen pickup or poor yield for these reactive alloys.
Hydrogenation-dehydrogenation (HDH) exploits the reversible hydrogen absorption of Ti, Zr, and Nb to induce embrittlement, enabling efficient crushing, followed by vacuum dehydrogenation to restore the alloy. This study systematically optimizes HDH parameters for equimolar TiZrNbTa, achieving low-oxygen powder with fine particle size, thereby addressing the bottleneck of producing high-quality RHEA powder for large-component manufacturing.
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CHEN Xing-yi, YAO Xin-wei, ZHANG Zhou-ran, TANG Yu, LI Shun (2026). Hydrogenation-Dehydrogenation Preparation of TiZrNbTa Refractory High-Entropy Alloy Powder. Chinese Journal of Energetic Materials (含能材料). https://doi.org/10.11943/CJEM2026026
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Frequently Asked Questions
What is the optimal hydrogenation temperature and pressure to achieve complete hydride formation without excessive oxygen pickup?
The optimal hydrogenation condition is 550 °C under 0.25 MPa hydrogen pressure for 2 h. This yields hydride powder with hydrogen content of 1.823% and oxygen content of 0.111%, indicating complete transformation to ZrH2, TiH2, and (Nb,Ta)H while limiting oxidation.
How does the dehydrogenation step affect particle size and oxygen content, and what are the trade-offs?
Dehydrogenation at 450 °C for 1.5 h reduces hydrogen to 0.028% but increases oxygen slightly to 0.121%. The particle size decreases from D50 = 11.13 μm to 5.67 μm, likely due to further fragmentation during vacuum treatment. Higher temperatures or longer times would reduce hydrogen further but increase oxygen, so 450 °C/1.5 h balances residual hydrogen and oxygen.
What is the scalability potential of this HDH process for industrial production of TiZrNbTa powder?
The process uses standard vacuum arc melting and vacuum hydrogenation furnaces, which are scalable. The achieved oxygen content (0.121%) is acceptable for powder metallurgy, and the fine particle size (5.67 μm) enhances sintering. However, batch-to-batch consistency and handling of reactive powders require controlled atmospheres, but the method is industrially viable.
How does the oxygen content of HDH powder compare to other methods, and what is its impact on mechanical properties?
The final oxygen content is 0.121%, which is lower than typical mechanical alloying (often >0.5%) and comparable to gas atomization but with finer particles. Low oxygen is critical to avoid embrittlement and maintain ductility in the final consolidated alloy, as oxygen interstitials can degrade fracture toughness.
What are the failure mechanisms if hydrogenation is performed at higher temperatures or pressures?
Higher temperatures or pressures increase hydrogen content and hydride formation, but also accelerate oxygen diffusion, leading to higher oxygen contamination. For example, at 0.4 MPa and higher temperatures, the oxygen content rises, which could compromise the mechanical properties of the final powder. Thus, 550 °C/0.25 MPa is optimal to balance hydride formation and oxidation.
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