Synthesis of nanostructured and spherical high-entropy alloy powders using a two-stage high-energy ball milling

In this study, a two-stage method for the spheroidization and nanostructuring of high-entropy alloy (HEA) powders was developed using high-energy ball milling (HEBM). The method is based on planetary HEBM of equiatomic elemental powders, employing varying ball sizes and rotation speeds of the milling jar and disk. Stage 1 (pre-alloying) used Ø6 mm 100Cr6 steel balls at a ball-to-powder ratio (BPR) of 15:1 and milling-jar/disk speeds of 1388/694 rpm (velocity ratio K = 2) for 30 min, with mechanical wall-cleaning every 10 min. Stage 2 (spheroidization) used Ø2 mm 100Cr6 steel balls at the same BPR of 15:1 and milling-jar/disk speeds of 300/300 rpm ( K = 1) for 15 h. Both stages were run in argon, in dry mode, without a process control agent (PCA). The process successfully produced spherical/quasi-spherical multiphase AlFeNiCuCrTi HEA powder with a narrow particle size distribution (PSD): 80% of the particles fall within the range of 5–45 μm (D₅₀ = 25 μm). The powder exhibits a homogeneous fine-grained microstructure (5–30 nm), comprising bcc (A2), fcc , and α -Ti phases, the intermetallic C14 Laves phase, and minor Al₂O₃ and Cr₂O₃ inclusions. The spheroidization method was validated on two-phase Al_0.3CoCrFeNi and single-phase CoCrFeNiMn HEA powders, which yielded larger particles and a narrower PSD. Approximately 80% of the particles fall within the range of 60–95 μm (Al_0.3CoCrFeNi) and 50–75 μm (CoCrFeNiMn), compared to 5–45 μm for AlFeNiCuCrTi. This difference is attributed to the more pronounced role of cold welding in the spheroidization process. Discrete element method simulations revealed that Stage 1 is dominated by a high-energy impact mode, while Stage 2 features more tangential contacts (sliding and rolling) with lower single-interaction energy. These changes in the kinematic process are consistent with the transition from fracture and flattening to surface smoothing and the formation of a spherical morphology. This simple, scalable method offers a promising route for producing HEA powders suitable for additive manufacturing.