Crystallization of undercooled liquid spinodals: Part II

Abstract

We demonstrated in “Phase separation in undercooled molten Pd₈₀Si₂₀: Part I” that when a molten Pd₈₀Si₂₀ 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 Pd₃Si, whereas the other one turns into Pd₉Si₂. In both cases, Pd particles precipitate out. Microstructural analysis indicates the Pd₃Si subnetwork forms first. It then acts as a seed for the subsequent crystallization of the remaining undercooled melt, which finally forms the Pd₉Si₂ dendrites. As crystallization proceeds, latent heat and volume contraction bring about morphological changes.