Kinetics of the Formation of a Disordered Crystal Structure during High-Speed Solidification

A phase–field description is given for the kinetic transition in the structure of a binary ordering crystal growing from a supercooled liquid. The results are interpreted on the basis of the solution of the phasefield dynamics equation and the relaxation equation for the long-range order parameter at the diffuse crystal–liquid interface and in the bulk of the crystal. The critical temperatures for the variation of the growth rate and the long-range order parameter of a growing A 50 B 50 crystal are determined. A qualitative difference and analogies are found between the processes of nonequilibrium impurity trapping and the formation of a disordered structure of rapidly growing crystals. The results of the study are analyzed in comparison with the results of the theory of kinetic phase transitions [A.A. Chernov, Sov. Phys. JETP 26 , 1182 (1967)] and the experimental data on the high-speed solidification of congruently melting samples [H. Hartmann et al., Europhys. Lett. 87 , 40007 (2009)].