RAPID CRYSTAL-GROWTH IN UNDERCOOLED FE-NI MELTS

Dendrite growth velocities have been measured as a function of undercooling DELTA-T on levitation undercooled Fe(1-x)Ni(x) melts of different concentrations (x = 0.30, 0.25). The growth velocities have been determined by measuring the recalescence times during crystallization by a high-speed photosensing device. The dendrite growth velocity V increases like a power law with undercooling DELTA-T up to a critical undercooling DELTA-T*. In this range the experimental data can be described within current theory of dendrite growth, when supposing primary crystallization of the f.c.c. phase. The transition at DELTA-T* to a weaker linear temperature dependence can be correlated to a grain refinement process.