A distinctive kinetics transition from stable hcp to metastable fcc dendrite growth within liquid Re₉₅W₅ refractory alloy

A transition of dendrite growth kinetics from stable hcp to metastable fcc phases was observed for refractory Re₉₅W₅ alloy in an electrostatic levitation state, which attained a liquid undercooling up to 872 K (0.26T _L). Stable hcp dendrite dominated in the single recalescence for pure Re in the whole of its undercooling regime, but prevailed for Re₉₅W₅ alloy only in the specific range of 159–867 K undercooling. The rapid dendrite growth velocity displayed a power-law relationship with the degree of undercooling. Once the refractory alloy melt was undercooled beyond 867 K undercooling, metastable fcc dendrite grew primarily from the liquid phase in the first recalescence, which was followed by a complete ‘fcc to hcp’ solid-state transformation in the second recalescence. An abrupt change of growth kinetics took place to depress the dendrite growth velocity drastically from 41.8 m·s⁻¹ for stable hcp phase at 867 K undercooling to 10.9 m·s⁻¹ for metastable fcc phase at 872 K undercooling.