Fluid Flow Effects on Growth Kinetics of undercooled Ni-Al Alloy Melts

Abstract

Fluid flow in Ni-Al alloy melts plays an important role for the formation of phases and microstructures during solidification due to its influence on heat and mass transport ahead of the solid-liquid interface. In particular, depending on the initial melt concentration the high degree of chemical order of intermetallic NiAl (B2-phase) requires a massive diffusion process during crystallization. Extensive ground based measurements on undercooled Ni-Al alloy melts show that the dendrite growth velocity of the intermetallic B2-phase is in the same order as the fluid flow velocity in the electromagnetically levitated samples. Therefore the fluid flow is supposed to play a decisive role for the microstructural evolution of Ni-Al intermetallics at small and intermediate undercooling levels. <p>The extension of existing models of dendritic growth capable of quantitatively describing the fluid flow effects on dendrite growth of intermetallic alloys is an important topic of current research within the ESA-MAP project ‘Non-Equilibrium Solidification, Modelling for Microstructure Engineering of Industrial Alloys’ (AO 98/99-023).</p> <p>The experiments on Ni-Al alloy melts during the parabolic flight campaign in May 2006 were crucial to test the models extension. The influence of convective flow on the growth kinetics of solidifying B2-phase and on the microstructural evolution of the retrieved specimens were investigated. </p>