  The crystallization of a binary system is investigated in computer model
which takes into account a temperature dependence of diffusion coefficient and
a nonequilibrium partition of dissolved component of the alloy. The dependence
of interface velocity on an undercooling at the dendrite tip is obtained during
rapid solidification of Fe-B and Ni-B systems. The morphological transition
which is conditioned by change from a diffusion growth regime to thermal growth
at some critical undercooling is detected. This transition is characterized by
discontinuous magnification of the dendrite growth velocity. Values of a
critical undercooling and a growth velocity discontinuity depend both on a
degree of an anisotropy of a kinetic coefficient, and on difference in energies
of activation for atomic kinetics and for diffusion on an interface.
