Change of the kinetics of solidification and microstructure formation induced by convection in the Ni–Al system

Abstract

The purpose of the present work was to measure the velocity of dendrite growth in undercooled Ni–Al alloy melts as a function of undercooling. The experiments were performed both by containerless electromagnetic levitation on Earth and under reduced gravity conditions during parabolic flight campaigns. While under terrestrial conditions, strong magnetic fields are required to compensate the gravitational force, the forces to compensate disturbing accelerations are decreased by orders of magnitude in reduced gravity. In turn, the alternating electromagnetic fields induce convection, which is strong under terrestrial conditions while much weaker in reduced gravity. The heat and mass transport in front of the solid-liquid interface during solidification controls the dynamics of dendrite growth. By comparing results obtained on Earth and in reduced gravity, it was demonstrated that the change of transport conditions by convection significantly alters the kinetics of solidification and the evolution of grain refined microstructures at undercoolings less than 100K.