Non-equilibrium and near-equilibrium solidification of undercooled melts of Ni- and Al-based alloys

Solidification behavior of industrially relevant materials such as Ni- and Al based alloys was investigated under conditions of containerless processing on Earth and reduced gravity using atomization and levitation experiments. A spray of small droplets is solidified in atomization processing during falling through a gas atmosphere with a large heat extraction rate. Levitation experiments allow for quantitative measurements of complete temperature-time- profiles and growth velocity of dendrites as a function of undercooling. Solidification of the undercooled melts take place in two steps as soon as nucleation sets in dendrites are formed and propagate rapidly through the undercooled melt under non-equilibrium conditions. Due to the rapid release of the heat of crystallization the undercooled melt is reheated during recalescence and the remaining interdendritic liquid solidifies under near equilibrium conditions during post recalescence period.