Spheroidization Behavior of TiZrNbTa Refractory High-Entropy Alloy Powder During Radio Frequency Plasma Processing

Spherical TiZrNbTa refractory high-entropy alloy powders with uniform composition and good flowability are essential feedstock for powder-based additive manufacturing; however, irregular powders produced by the hydrogenation-dehydrogenation route generally require further shaping treatment. Radio frequency (RF) plasma spheroidization of TiZrNbTa refractory high-entropy alloy powders prepared by hydrogenation-dehydrogenation (HDH) was investigated at a fixed power of 12 kW. Fine (10–40 μm) and coarse (40–70 μm) powders were compared at 5.0 g/min, followed by feed-rate tests (2.5–7.5 g/min) on the coarse fraction. At 5.0 g/min, the spheroidization degrees of the fine and coarse powders were 45.33% and 50.88%, respectively. The fine powder exhibited satellite particles and a broadened particle-size distribution, whereas the coarse powder retained some irregular particles. Decreasing the coarse-powder feed rate from 7.5 to 2.5 g/min increased the spheroidization degree from 45.71% to 94.55%, with median particle size (D50) reaching 56.84 μm and a narrower particle-size distribution. The powders retained predominantly body-centered cubic (BCC) diffraction signatures, while dendritic substructures and local Ta/Zr segregation varied with processing conditions. Testing showed that untreated coarse HDH powder did not flow unaided through a Hall funnel, whereas the 5.0 g/min spheroidized product flowed in 18.7 s/50 g; after spheroidization, its loose bulk density increased from 4.68 to 5.47 g/cm3. These results clarify the effects of particle size and powder feed rate on spheroidization behavior within the investigated conditions.