Microstructure and phase selection in containerless processing of Fe-Ni droplets.

Fe–Ni droplets (Ni content 0–30 at.%) were containerlessly processed by electromagnetic levitation, in a drop-tube or by atomization. The droplet diameter varied from 10 μm to 7 mm. The competition between the formation of b.c.c. and c.c.p. phases is elucidated by studies of the recalescence behaviour and the dendrite growth velocities as a function of undercooling. For levitation the results are summarized in a phase-selection map. For droplets produced in the spray methods, a selection map was constructed which relates the predominant phases and microstructures (coarse-dendritic or grain-refined) to the composition and the droplet size. Links are established between the final microstructures, the crystal phases and the processing conditions. Thermodynamic modelling (CALPHAD) and an analysis of dendrite growth velocities are used to analyse the nucleation and growth behaviour.