Primary dendrite growth within binary Fe₇₁Ge₂₉ eutectic alloy under duplex levitation states

The primary β-Fe₃Ge₂ dendrite growth kinetics within liquid Fe₇₁Ge₂₉ eutectic alloy was studied by both acoustic levitation and electrostatic levitation techniques, with maximum experimental undercoolings of 130 and 143 K, respectively. At small undercoolings, (α₁ + β-Fe₃Ge₂) eutectic growth proceeded and then transformed to lamellar (ϵ-Fe₃Ge + β-Fe₃Ge₂) microstructure by peritectoid reaction. Once liquid undercooling reached 56 K, β primary phase started to nucleate preferentially and its maximum growth velocity attained 13.5 mm/s at 143 K undercooling. By acoustic levitation processing, β dendrites were distributed inside the alloy droplet. Under electrostatic levitation state, β dendrites were distributed both at the periphery and within the interior of alloy droplet, and their volume fraction was significantly higher than that under acoustic levitation. Numerical simulation results indicated that a duplex flow was induced by alloy droplet shape oscillation and acoustic streaming. The flow exhibited maximum intensity near the alloy surface, which inhibited the achievement of larger undercoolings during acoustic levitation.