Crystallization of undercooled liquid spinodals: Part II

摘要

We demonstrated in "Phase separation in undercooled molten Pd_80Si_20: Part I" that when a molten Pd_80Si_20 ingot is undercooled into its undercooling regimen with ΔT ≥ 220 K (ΔT = T_1 - T, where T_1 is the liquidus and T is the temperature of the undercooled melt), liquid-state phase separation by spinodal decomposition occurs. On crystallization, one of the metastable liquid spinodals becomes Pd_3Si, whereas the other one turns into Pd_9Si_2. In both cases, Pd particles precipitate out. Microstructural analysis indicates the Pd_3Si subnetwork forms first. It then acts as a seed for the subsequent crystallization of the remaining undercooled melt, which finally forms the Pd_9Si_2 dendrites. As crystallization proceeds, latent heat and volume contraction bring about morphological changes.