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.