Competitive nucleation and growth of (Ge) and CuAl 2 phases subjected to different solidification conditions (Phys. Status Solidi B 2/2015)

Rapid solidification is a liquid/solid phase transition process deviating far from the equilibrium situation, which consequently influences the mechanical property and processability of a metallic material. Drop tube technique solidifies an alloy sample into micron‐sized droplets with a high cooling rate during free fall. Under such rapid solidification condition featured by microgravity and containerless state, the nucleation and growth behavior of multi‐phases from the substantially undercooled melt become more competitive. Besides, for the alloy droplets solidifying in the drop tube, the effects of heat transfer and fluid flow on solidification are also complicated. Ruan and Wang (pp. 361–364 ) investigate the competitive nucleation and growth of (Ge) and CuAl 2 phases in Al‐Cu‐Ge ternary alloy by means of drop tube processing in comparison with near‐equilibrium solidification realized by the differential scanning calorimetry (DSC) method, according to the solidification pathway and microstructural characteristics. Once the alloy droplet diameter is less than ̃200 μm, the leading nucleation of (Ge) phase is replaced by the simultaneous nucleation of (Ge) and CuAl 2 phases due to a further increase of undercooling and especially the cooling rate. This results in the microstructural transition to anomalous eutectic grains plus intercrystalline (Al) phase.